the essay of human understanding

A Summary and Analysis of John Locke’s An Essay Concerning Human Understanding

By Dr Oliver Tearle (Loughborough University)

Published in 1689 though formally dated 1690, John Locke’s An Essay Concerning Human Understanding is one of the most important works of Enlightenment philosophy: indeed, in many ways, Locke paved the way for the (later) Enlightenment.

But what is it about An Essay Concerning Human Understanding , and Locke’s argument, which makes him so important?

You can read the whole of An Essay Concerning Human Understanding here (the text is taken from the original 1689 edition, which erroneously gave the title as An Essay Concerning Humane Understanding ), but we’ve tried to summarise the main points of Locke’s argument below, before proceeding to an analysis of his meaning – and his significance.

An Essay Concerning Human Understanding : summary

Locke begins the Essay by arguing against the earlier rationalist idea (propounded by Descartes among others) that ideas can be innate within the human mind. For Locke, when babies are born their minds are empty: a notion which he famously calls the tabula rasa (literally, ‘blank slate’). Human minds are like a blank sheet of paper when we’re born, and everything that ends up in them is supplied by experience.

This signals Locke’s adherence to empiricism over rationalism: rather than believing knowledge and ideas about the world are in-built within us by nature, he believes that ideas are acquired from external stimuli, from us going out there into the world and being exposed to things.

Book II develops this idea in more detail. Experience is the bedrock of all human knowledge. We don’t inherently ‘know’ things: we learn about things as we experience them. This is a bit like a ‘nurture over nature’ view. There are two routes to knowledge via experience: sensation and reflection . Sensation is about coming into contact with the external world, whereas reflection comes from introspection, or from reflecting on what we have experienced.

Book III proposes an idea later developed in more depth by Immanuel Kant: that we cannot ever know true reality, only our perception of it. And our perception of reality is necessarily subjective: you don’t have precisely the same experience of the world as I do. It is also in Book III that Locke attempts to apply his empiricist approach to language.

Book IV appears, on the face of it, to contradict what Locke had set out to argue: namely, that empiricism rather than rationalism is the correct way to view knowledge. But he is actually arguing that, once we adopt an empirical mindset, we are then able to draw a rationalist conclusion of the world from that experience.

An Essay Concerning Human Understanding : analysis

The twentieth-century philosopher Isaiah Berlin once suggested that John Locke effectively invented the idea of common sense in matters of philosophy, and An Essay Concerning Human Understanding is certainly a powerful defence of the importance of an empiricist outlook, whereby we trust our own senses and experiences rather than simply assuming things to be innately true and unquestionable. Bertrand Russell made a similar claim about Locke’s book.

What this means is that Locke’s contribution to philosophy lies partly in his emphasis on the importance of experience in forming our ideas and values. Empiricism places the emphasis on our own sensory understanding of the world (what is now sometimes called ‘lived experience’, to offer a broader term).

This means that we trust our own senses rather than some innate knowledge we come pre-programmed with at birth. How do we know right from wrong? Locke would argue that we have to learn what ‘right’ and ‘wrong’ mean in order to know that.

Locke is, of course, right to emphasise the importance of experience in forming our knowledge of the world. But, in his determination to oppose the rationalist approach touted by Spinoza, Descartes, and others, does he take things too far in the other direction?

There are many moral philosophers who would argue that we do have an innate sense of right and wrong which is present at birth, even if we’re too young to act on it as soon as we leave the womb. Evolutionary biologists would argue that we wouldn’t have got as far as we have as a species without this in-built sense of morality, among other things.

There are other aspects of An Essay Concerning Human Understanding which critics have argued are too reductive. Although our own experience is obviously important in shaping our view of the world, few would go so far as Locke and argue that it’s the only significant factor.

For one thing, our experience of the world is just too different: a man living in a secluded monastery in Yorkshire is unlikely to arrive at the same ‘knowledge’ of the world as a midwife working in London. Locke grants that our experiences will necessarily be subjective, but where does that leave us when considering supposedly self-evident or universal truths, such as ‘killing is wrong’ or ‘do unto others as you would have them to do you’?

Nevertheless, An Essay Concerning Human Understanding is an important book, not least because it was a milestone in philosophy and would act as the foundation for the work of many philosophers who came after Locke.

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Locke remained in Holland for more than five years (1683–89). While there he made new and important friends and associated with other exiles from England. He also wrote his first Letter on Toleration , published anonymously in Latin in 1689, and completed An Essay Concerning Human Understanding .

A dominant theme of the Essay is the question with which the original discussion in Exeter House began: What is the capacity of the human mind for understanding and knowledge ? In his prefatory chapter, Locke explains that the Essay is not offered as a contribution to knowledge itself but as a means of clearing away some of the intellectual rubbish that stands in the way of knowledge. He had in mind not only the medieval Scholastics and their followers but also some of his older contemporaries. The Scholastics—those who took Aristotle and his commentators to be the source of all philosophical knowledge and who still dominated teaching in universities throughout Europe—were guilty of introducing technical terms into philosophy (such as substantial form , vegetative soul , abhorrence of a vacuum , and intentional species ) that upon examination had no clear sense—or, more often, no sense at all. Locke saw the Scholastics as an enemy that had to be defeated before his own account of knowledge could be widely accepted, something about which he was entirely right.

Locke begins the Essay by repudiating the view that certain kinds of knowledge—knowledge of the existence of God , of certain moral truths, or of the laws of logic or mathematics —are innate, imprinted on the human mind at its creation. (The doctrine of innate ideas , which was widely held to justify religious and moral claims, had its origins in the philosophy of Plato [428/427–348/347 bce ], who was still a powerful force in 17th-century English philosophy.) Locke argues to the contrary that an idea cannot be said to be “in the mind” until one is conscious of it. But human infants have no conception of God or of moral, logical, or mathematical truths, and to suppose that they do, despite obvious evidence to the contrary, is merely an unwarranted assumption to save a position. Furthermore, travelers to distant lands have reported encounters with people who have no conception of God and who think it morally justified to eat their enemies. Such diversity of religious and moral opinion cannot not be explained by the doctrine of innate ideas but can be explained, Locke held, on his own account of the origins of ideas.

In Book II he turns to that positive account. He begins by claiming that the sources of all knowledge are, first, sense experience (the red colour of a rose, the ringing sound of a bell, the taste of salt, and so on) and, second, “ reflection ” (one’s awareness that one is thinking , that one is happy or sad, that one is having a certain sensation, and so on). These are not themselves, however, instances of knowledge in the strict sense, but they provide the mind with the materials of knowledge. Locke calls the materials so provided “ideas.” Ideas are objects “before the mind,” not in the sense that they are physical objects but in the sense that they represent physical objects to consciousness .

All ideas are either simple or complex. All simple ideas are derived from sense experience, and all complex ideas are derived from the combination (“compounding”) of simple and complex ideas by the mind. Whereas complex ideas can be analyzed, or broken down, into the simple or complex ideas of which they are composed, simple ideas cannot be. The complex idea of a snowball, for example, can be analyzed into the simple ideas of whiteness, roundness, and solidity (among possibly others), but none of the latter ideas can be analyzed into anything simpler. In Locke’s view, therefore, a major function of philosophical inquiry is the analysis of the meanings of terms through the identification of the ideas that give rise to them. The project of analyzing supposedly complex ideas (or concepts) subsequently became an important theme in philosophy, especially within the analytic tradition, which began at the turn of the 20th century and became dominant at Cambridge , Oxford , and many other universities, especially in the English-speaking world.

In the course of his account, Locke raises a host of related issues, many of which have since been the source of much debate. One of them is his illuminating distinction between the “primary” and “secondary” qualities of physical objects. Primary qualities include size, shape, weight, and solidity, among others, and secondary qualities include colour, taste, and smell. Ideas of primary qualities resemble the qualities as they are in the object—as one’s idea of the roundness of a snowball resembles the roundness of the snowball itself. However, ideas of secondary qualities do not resemble any property in the object; they are instead a product of the power that the object has to cause certain kinds of ideas in the mind of the perceiver. Thus, the whiteness of the snowball is merely an idea produced in the mind by the interaction between light, the primary qualities of the snowball, and the perceiver’s sense organs.

Locke discussed another problem that had not before received sustained attention: that of personal identity . Assuming one is the same person as the person who existed last week or the person who was born many years ago, what fact makes this so? Locke was careful to distinguish the notion of sameness of person from the related notions of sameness of body and sameness of man, or human being . Sameness of body requires identity of matter, and sameness of human being depends on continuity of life (as would the sameness of a certain oak tree from acorn to sapling to maturity); but sameness of person requires something else. Locke’s proposal was that personal identity consists of continuity of consciousness . One is the same person as the person who existed last week or many years ago if one has memories of the earlier person’s conscious experiences. Locke’s account of personal identity became a standard (and highly contested) position in subsequent discussions.

A further influential section of Book II is Locke’s treatment of the association of ideas . Ideas, Locke observes, can become linked in the mind in such a way that having one idea immediately leads one to form another idea, even though the two ideas are not necessarily connected with each other. Instead, they are linked through their having been experienced together on numerous occasions in the past. The psychological tendency to associate ideas through experience, Locke says, has important implications for the education of children. In order to learn to adopt good habits and to avoid bad ones, children must be made to associate rewards with good behaviour and punishments with bad behaviour. Investigations into the associations that people make between ideas can reveal much about how human beings think. Through his influence on researchers such as the English physician David Hartley (1705–57), Locke contributed significantly to the development of the theory of associationism, or associationist psychology, in the 18th century. Association has remained a central topic of inquiry in psychology ever since.

Having shown to his satisfaction that no idea requires for its explanation the hypothesis of innate ideas, Locke proceeds in Book III to examine the role of language in human mental life. His discussion is the first sustained philosophical inquiry in modern times into the notion of linguistic meaning. As elsewhere, he begins with rather simple and obvious claims but quickly proceeds to complex and contentious ones. Words , Locke says, stand for ideas in the mind of the person who uses them. It is by the use of words that people convey their necessarily private thoughts to each other. In addition, Locke insists, nothing exists except particulars, or individual things. There are, for example, many triangular things and many red things, but there is no general quality or property, over and above these things, that may be called “triangle” (“triangularity”) or “red” (“redness”) ( see universal ). Nevertheless, a large number of words are general in their application, applying to many particular things at once. Thus, words must be labels for both ideas of particular things (particular ideas) and ideas of general things (general ideas). The problem is, if everything that exists is a particular, where do general ideas come from?

Locke’s answer is that ideas become general through the process of abstraction. The general idea of a triangle, for example, is the result of abstracting from the properties of specific triangles only the residue of qualities that all triangles have in common—that is, having three straight sides. Although there are enormous problems with this account, alternatives to it are also fraught with difficulties.

In Book IV of the Essay , Locke reaches the putative heart of his inquiry, the nature and extent of human knowledge. His precise definition of knowledge entails that very few things actually count as such for him. In general, he excludes knowledge claims in which there is no evident connection or exclusion between the ideas of which the claim is composed. Thus, it is possible to know that white is not black whenever one has the ideas of white and black together (as when one looks at a printed page), and it is possible to know that the three angles of a triangle equal two right angles if one knows the relevant Euclidean proof. But it is not possible to know that the next stone one drops will fall downward or that the next glass of water one drinks will quench one’s thirst, even though psychologically one has every expectation, through the association of ideas, that it will. These are cases only of probability, not knowledge—as indeed is virtually the whole of scientific knowledge, excluding mathematics . Not that such probable claims are unimportant: humans would be incapable of dealing with the world except on the assumption that such claims are true. But for Locke they fall short of genuine knowledge.

There are, however, some very important things that can be known. For example, Locke agreed with Descartes that each person can know immediately and without appeal to any further evidence that he exists at the time that he considers it. One can also know immediately that the colour of the print on a page is different from the colour of the page itself—i.e., that black is not white—and that two is greater than one. It can also be proved from self-evident truths by valid argument (by an argument whose conclusion cannot be false if its premises are true) that a first cause , or God, must exist. Various moral claims also can be demonstrated—e.g., that parents have a duty to care for their children and that one should honour one’s contracts. People often make mistakes or poor judgments in their dealings with the world or each other because they are unclear about the concepts they use or because they fail to analyze the relevant ideas. Another great cause of confusion, however, is the human propensity to succumb to what Locke calls “Enthusiasm,” the adoption on logically inadequate grounds of claims that one is already disposed to accept.

One major problem that the Essay appeared to raise is that if ideas are indeed the immediate objects of experience, how is it possible to know that there is anything beyond them—e.g., ordinary physical objects? Locke’s answer to this problem, insofar as he recognized it as a problem, appears to have been that, because perception is a natural process and thus ordained by God, it cannot be generally misleading about the ontology of the universe. In the more skeptical age of the 18th century, this argument became less and less convincing. This issue dominated epistemology in the 18th century.

The Essay ’s influence was enormous, perhaps as great as that of any other philosophical work apart from those of Plato and Aristotle . Its importance in the English-speaking world of the 18th century can scarcely be overstated. Along with the works of Descartes, it constitutes the foundation of modern Western philosophy .

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6 John Locke’s (1632–1704) Essay Concerning Human Understanding (1689)

The project of the essay, against innate knowledge, ideas and their origin, simple ideas, primary and secondary qualities, complex ideas, substance/substratum, natural kinds, personal identity, the limits of knowledge.

As Locke admits, his Essay is something of a mess, from an editorial point of view. What follows are what I take to be some of the most important passages from the book, grouped under topical headings in an attempt to make a coherent and systematic whole. Parts and headings are given in bold and are purely my invention. Section headings are given in italics, and are Locke’s. Otherwise, all material in italics is mine, not Locke’s. ‘…’ indicates an omission.

The Essay is organized into Books, Chapters, and Sections. The start of each section cites book.chapter.section. For example, ‘I.i.5’ means Book I, chapter i, section 5.

(Textual note: the standard edition of the Essay is that of P.H. Nidditch (Oxford, 1975); but Roger Woolhouse’s Penguin edition is superior in some respects.)

<!–The headings are as follows: A. The Project B. Against Innate Knowledge C. Ideas and their Origin D. Simple Ideas E. Primary and Secondary Qualities F. Complex Ideas G. Substance/substratum H. Natural Kinds I. Body J. Mind K. Personal Identity L. The Limits of Knowledge M. God–>

(From The Epistle to the Reader ) Were it fit to trouble thee with the history of this Essay, I should tell thee, that five or six friends meeting at my chamber, and discoursing on a subject very remote from this, found themselves quickly at a stand, by the difficulties that rose on every side. After we had awhile puzzled ourselves, without coming any nearer a resolution of those doubts which perplexed us, it came into my thoughts that we took a wrong course; and that before we set ourselves upon inquiries of that nature, it was necessary to examine our own abilities, and see what objects our understandings were, or were not, fitted to deal with. …

The commonwealth of learning is not at this time without master-builders, whose mighty designs, in advancing the sciences, will leave lasting monuments to the admiration of posterity: but every one must not hope to be a Boyle or a Sydenham; and in an age that produces such masters as the great Huygenius and the incomparable Mr. Newton, with some others of that strain, it is ambition enough to be employed as an under-labourer in clearing the ground a little, and removing some of the rubbish that lies in the way to knowledge …

(From I.i.1— An Inquiry into the Understanding pleasant and useful ) Since it is the understanding that sets man above the rest of sensible beings, and gives him all the advantage and dominion which he has over them; it is certainly a subject, even for its nobleness, worth our labour to inquire into. The understanding, like the eye, whilst it makes us see and perceive all other things, takes no notice of itself; and it requires and art and pains to set it at a distance and make it its own object. …

(From I.i.2— Design ) This, therefore, being my purpose–to inquire into the original, certainty, and extent of human knowledge , together with the grounds and degrees of belief , opinion , and assent …

(From I.i.3— Method ) It is therefore worth while to search out the bounds between opinion and knowledge; and examine by what measures, in things whereof we have no certain knowledge, we ought to regulate our assent and moderate our persuasion. In order whereunto I shall pursue this following method: First, I shall inquire into the original of those ideas, notions, or whatever else you please to call them, which a man observes, and is conscious to himself he has in his mind; and the ways whereby the understanding comes to be furnished with them. Secondly, I shall endeavour to show what knowledge the understanding hath by those ideas; and the certainty, evidence, and extent of it. Thirdly, I shall make some inquiry into the nature and grounds of faith or opinion : whereby I mean that assent which we give to any proposition as true, of whose truth yet we have no certain knowledge. And here we shall have occasion to examine the reasons and degrees of assent .

(From I.i.4— Useful to know the Extent of our Comprehension ) If we can find out how far the understanding can extend its view; how far it has faculties to attain certainty; and in what cases it can only judge and guess, we may learn to content ourselves with what is attainable by us in this state.

(From I.i.5— Our Capacity suited to our State and Concerns ) It will be no excuse to an idle and untoward servant, who would not attend his business by candle light, to plead that he had not broad sunshine. The Candle that is set up in us shines bright enough for all our purposes.

(From I.i.6— Knowledge of our Capacity a Cure of Scepticism and Idleness ) When we know our own strength, we shall the better know what to undertake with hopes of success; and when we have well surveyed the powers of our own minds, and made some estimate what we may expect from them, we shall not be inclined either to sit still, and not set our thoughts on work at all, in despair of knowing anything; nor on the other side, question everything, and disclaim all knowledge, because some things are not to be understood. It is of great use to the sailor to know the length of his line, though he cannot with it fathom all the depths of the ocean. It is well he knows that it is long enough to reach the bottom, at such places as are necessary to direct his voyage, and caution him against running upon shoals that may ruin him. Our business here is not to know all things, but those which concern our conduct. If we can find out those measures, whereby a rational creature, put in that state in which man is in this world, may and ought to govern his opinions, and actions depending thereon, we need not to be troubled that some other things escape our knowledge.

• What is Locke’s main project in the Essay?
• What’s the point of pursuing it? What advantages does he expect to obtain from it?
• What is distinctive about Locke’s project? What would Locke think of the method of, say, Spinoza?

Given Locke’s project, it makes sense that he begins by attacking the doctrine of innate knowledge. This attack was partly responsible for the Essay ’s being banned at Oxford in 1704. Can you think why these thoughts might sound dangerous, and why Locke’s project begins where it does?

(From I.ii.5– Not on Mind naturally imprinted, because not known to Children, Idiots, &c. ) For, first, it is evident, that all children and idiots have not the least apprehension or thought of them. And the want of that is enough to destroy that universal assent which must needs be the necessary concomitant of all innate truths: it seeming to me near a contradiction to say, that there are truths imprinted on the soul, which it perceives or understands not: imprinting, if it signify anything, being nothing else but the making certain truths to be perceived. For to imprint anything on the mind without the mind’s perceiving it, seems to me hardly intelligible. If therefore children and idiots have souls, have minds, with those impressions upon them, they must unavoidably perceive them …

[I]f the capacity of knowing be the natural impression contended for, all the truths a man ever comes to know will, by this account, be every one of them innate; and this great point will amount to no more, but only to a very improper way of speaking; which, whilst it pretends to assert the contrary, says nothing different from those who deny innate principles. For nobody, I think, ever denied that the mind was capable of knowing several truths.

(From I.ii.15— The Steps by which the Mind attains several Truths ) The senses at first let in particular ideas, and furnish the yet empty cabinet, and the mind by degrees growing familiar with some of them, they are lodged in the memory, and names got to them. Afterwards, the mind proceeding further, abstracts them, and by degrees learns the use of general names. In this manner the mind comes to be furnished with ideas and language, the materials about which to exercise its discursive faculty. And the use of reason becomes daily more visible, as these materials that give it employment increase. But though the having of general ideas and the use of general words and reason usually grow together, yet I see not how this any way proves them innate.

(From I.iv.20— No innate Ideas in the Memory ) To which let me add: if there be any innate ideas, any ideas in the mind which the mind does not actually think on, they must be lodged in the memory; and from thence must be brought into view by remembrance; i.e., must be known, when they are remembered, to have been perceptions in the mind before; unless remembrance can be without remembrance. For, to remember is to perceive anything with memory, or with a consciousness that it was perceived or known before. Without this, whatever idea comes into the mind is new, and not remembered; this consciousness of its having been in the mind before, being that which distinguishes remembering from all other ways of thinking.

Whatever idea was never perceived by the mind was never in the mind. Whatever idea is in the mind, is, either an actual perception, or else, having been an actual perception, is so in the mind that, by the memory, it can be made an actual perception again. Whenever there is the actual perception of any idea without memory, the idea appears perfectly new and unknown before to the understanding. Whenever the memory brings any idea into actual view, it is with a consciousness that it had been there before, and was not wholly a stranger to the mind. Whether this be not so, I appeal to every one’s observation. And then I desire an instance of an idea, pretended to be innate, which (before any impression of it by ways hereafter to be mentioned) any one could revive and remember, as an idea he had formerly known; without which consciousness of a former perception there is no remembrance; and whatever idea comes into the mind without that consciousness is not remembered, or comes not out of the memory, nor can be said to be in the mind before that appearance. For what is not either actually in view or in the memory, is in the mind no way at all, and is all one as if it had never been there. …

[W]hatever idea, being not actually in view, is in the mind, is there only by being in the memory; and if it be not in the memory, it is not in the mind; and if it be in the memory, it cannot by the memory be brought into actual view without a perception that it comes out of the memory; which is this, that it had been known before, and is now remembered. If therefore there be any innate ideas, they must be in the memory, or else nowhere in the mind; and if they be in the memory, they can be revived without any impression from without; and whenever they are brought into the mind they are remembered, i. E. They bring with them a perception of their not being wholly new to it. …

By this it may be tried whether there be any innate ideas in the mind before impression from sensation or reflection. I would fain meet with the man who, when he came to the use of reason, or at any other time, remembered any of them; and to whom, after he was born, they were never new. If any one will say, there are ideas in the mind that are not in the memory, I desire him to explain himself, and make what he says intelligible.

• Why is Locke concerned to deny the doctrine of innate principles? Can you connect this with Locke’s project?
• Can you extract an argument from these texts that might apply to innate ideas (as opposed to principles)? There seem to be three possible ways to cash out what it means to say that an idea is innate. It might be innate as a capacity; it might always be present to the mind; or it might be lodged in the memory. What does Locke think is wrong with this last option (memory)? (See esp. Chapter 4, Section 20 above—hint: Locke seems to think there’s something contradictory about innateness.)

Premise 1: An innate idea is in the memory. Premise 2: Any idea in the memory, when recovered, brings with it…

It’s one thing to attack the doctrines of innate knowledge and innate ideas; it’s another to come up with a replacement for them. Locke must explain how all our ideas are generated solely out of the materials given to us in experience, and how experience alone can justify our knowledge claims.

(From I.1.8— What Idea stands for ) Thus much I thought necessary to say concerning the occasion of this inquiry into human understanding. But, before I proceed on to what I have thought on this subject, I must here in the entrance beg pardon of my reader for the frequent use of the word idea , which he will find in the following treatise. It being that term which, I think, serves best to stand for whatsoever is the object of the understanding when a man thinks, I have used it to express whatever is meant by phantasm, notion, species , or whatever it is which the mind can be employed about in thinking ; and I could not avoid frequently using it. I presume it will be easily granted me, that there are such ideas in men’s minds: every one is conscious of them in himself; and men’s words and actions will satisfy him that they are in others.

(From IV.xxi.4) [S]ince the things the mind contemplates are none of them, besides itself, present to the understanding, it is necessary that something else, as a sign or representation of the thing it considers, should be present to it: and these are ideas .

(From II.i.2— All Ideas come from Sensation or Reflection ) Let us then suppose the mind to be, as we say, white paper, void of all characters, without any ideas: how comes it to be furnished? … To this I answer, in one word, from experience . In that all our knowledge is founded; and from that it ultimately derives itself. Our observation employed either, about external sensible objects, or about the internal operations of our minds perceived and reflected on by ourselves, is that which supplies our understandings with all the materials of thinking. These two are the fountains of knowledge, from whence all the ideas we have, or can naturally have, do spring.

(From II.i.3— The Objects of Sensation one Source of Ideas ) First, our senses, conversant about particular sensible objects, do convey into the mind several distinct perceptions of things, according to those various ways wherein those objects do affect them. And thus we come by those ideas we have of yellow, white, heat, cold, soft, hard, bitter, sweet, and all those which we call sensible qualities …

(From II.i.4— The Operations of our Minds, the other Source of them ) Secondly, the other fountain from which experience furnisheth the understanding with ideas is, the perception of the operations of our own mind within us, as it is employed about the ideas it has got. … And such are perception, thinking, doubting, believing, reasoning, knowing, willing, and all the different actings of our own minds …

(From II.i.5— All our Ideas are of the one or of the other of these ) … These, when we have taken a full survey of them, and their several modes, and the compositions made out of them we shall find to contain all our whole stock of ideas; and that we have nothing in our minds which did not come in one of these two ways. Let any one examine his own thoughts, and thoroughly search into his understanding; and then let him tell me, whether all the original ideas he has there, are any other than of the objects of his senses, or of the operations of his mind, considered as objects of his reflection.

Locke thinks that sensation and reflection are our only sources of ideas. We should now look at his response to Descartes’s argument for a third source of ideas, namely, the intellect (see the second paragraph of the Sixth Meditation .

(From II.xxix.13— Complex ideas may be distinct in one part, and confused in another ) Our complex ideas, being made up of collections, and so variety of simple ones, may accordingly be very clear and distinct in one part, and very obscure and confused in another. In a man who speaks of a chiliaedron, or a body of a thousand sides, the ideas of the figure may be very confused, though that of the number be very distinct; so that he being able to discourse and demonstrate concerning that part of his complex idea which depends upon the number of thousand, he is apt to think he has a distinct idea of a chiliaedron; though it be plain he has no precise idea of its figure, so as to distinguish it, by that, from one that has but 999 sides: the not observing whereof causes no small error in men’s thoughts, and confusion in their discourses.

• How does Locke respond to Descartes’s argument for the distinction between the intellect and the imagination? Who is right?

(From II.i.1— Uncompounded Appearances ) The better to understand the nature, manner, and extent of our knowledge, one thing is carefully to be observed concerning the ideas we have; and that is, that some of them, are simple and some complex .

Though the qualities that affect our senses are, in the things themselves, so united and blended, that there is no separation, no distance between them; yet it is plain, the ideas they produce in the mind enter by the senses simple; and unmixed. For, though the sight and touch often take in from the same object, at the same time, different ideas;–as a man sees at once motion and colour; the hand feels softness and warmth in the same piece of wax: yet the simple ideas thus united in the same subject, are as perfectly distinct as those that come in by different senses.

(From II.iii.1— Division of simple ideas ) The better to conceive the ideas we receive from sensation, it may not be amiss for us to consider them, in reference to the different ways whereby they make their approaches to our minds, and make themselves perceivable by us. First , then, there are some which come into our minds by one sense only . Secondly , there are others that convey themselves into the mind by more senses than one . Thirdly , others that are had from reflection only . Fourthly , there are some that make themselves way, and are suggested to the mind by all the ways of sensation and reflection .

• the idea of blue ___________
• the idea of square ___________
• the idea of hoping ___________
• the idea of straight ___________

(From II.xxi.1— This Idea [of power] how got ) The mind being every day informed, by the senses, of the alteration of those simple ideas it observes in things without; and taking notice how one comes to an end, and ceases to be, and another begins to exist which was not before; reflecting also on what passes within itself, and observing a constant change of its ideas, sometimes by the impression of outward objects on the senses, and sometimes by the determination of its own choice; and concluding from what it has so constantly observed to have been, that the like changes will for the future be made in the same things, by like agents, and by the like ways, considers in one thing the possibility of having any of its simple ideas changed, and in another the possibility of making that change; and so comes by that idea which we call power . Thus we say, fire has a power to melt gold, i.e., to destroy the consistency of its insensible parts, and consequently its hardness, and make it fluid … In which, and the like cases, the power we consider is in reference to the change of perceivable ideas. For we cannot observe any alteration to be made in, or operation upon anything, but by the observable change of its sensible ideas; nor conceive any alteration to be made, but by conceiving a change of some of its ideas.

(From II.xxi.2— Power, active and passive ) Power thus considered is two-fold, viz. As able to make, or able to receive any change. The one may be called active , and the other passive power. Whether matter be not wholly destitute of active power, as its author, God, is truly above all passive power; and whether the intermediate state of created spirits be not that alone which is capable of both active and passive power, may be worth consideration. I shall not now enter into that inquiry, my present business being not to search into the original of power, but how we come by the idea of it. But since active powers make so great a part of our complex ideas of natural substances, (as we shall see hereafter,) and I mention them as such, according to common apprehension; yet they being not, perhaps, so truly active powers as our hasty thoughts are apt to represent them, I judge it not amiss, by this intimation, to direct our minds to the consideration of god and spirits, for the clearest idea of active power.

(From II.xxi.3— Power includes Relation ) I confess power includes in it some kind of relation (a relation to action or change,) as indeed which of our ideas of what kind soever, when attentively considered, does not. For, our ideas of extension, duration, and number, do they not all contain in them a secret relation of the parts? figure and motion have something relative in them much more visibly. … Our idea therefore of power, I think, may well have a place amongst other simple ideas , and be considered as one of them; being one of those that make a principal ingredient in our complex ideas of substances, as we shall hereafter have occasion to observe.

(From II.xxi.4— The clearest Idea of active Power had from Spirit ) [I]f we will consider it attentively, bodies, by our senses, do not afford us so clear and distinct an idea of active power, as we have from reflection on the operations of our minds. For all power relating to action, and there being but two sorts of action whereof we have an idea, viz. Thinking and motion, let us consider whence we have the clearest ideas of the powers which produce these actions.

Of thinking, body affords us no idea at all; it is only from reflection that we have that. Neither have we from body any idea of the beginning of motion. A body at rest affords us no idea of any active power to move; and when it is set in motion itself, that motion is rather a passion than an action in it. For, when the ball obeys the motion of a billiard-stick, it is not any action of the ball, but bare passion. Also when by impulse it sets another ball in motion that lay in its way, it only communicates the motion it had received from another, and loses in itself so much as the other received: which gives us but a very obscure idea of an active power of moving in body, whilst we observe it only to transfer , but not produce any motion.

• Is the idea of power a simple idea or not? What turns on this?
• How does the mind form an idea of power?
• Why does sensation not give us an idea of active power?

II.viii is intended as a further discussion of simple ideas. Locke draws what should by now be a familiar distinction. Can you reconstruct Locke’s argument?

(From II.viii.7— Ideas in the Mind, Qualities in Bodies ) To discover the nature of our ideas the better, and to, discourse of them intelligibly, it will be convenient to distinguish them as they are ideas or perceptions in our minds ; and as they are modifications of matter in the bodies that cause such perceptions in us …

(From II.viii.8— Our Ideas and the Qualities of Bodies ) Whatsoever the mind perceives in itself , or is the immediate object of perception, thought, or understanding, that I call idea ; and the power to produce any idea in our mind, I call quality of the subject wherein that power is. Thus a snowball having the power to produce in us the ideas of white, cold, and round—the power to produce those ideas in us, as they are in the snowball, I call qualities; and as they are sensations or perceptions in our understandings, I call them ideas; which ideas , if I speak of sometimes as in the things themselves, I would be understood to mean those qualities in the objects which produce them in us.

(From II.viii.9— Primary Qualities of Bodies ) Concerning these qualities, we, I think, observe these primary ones in bodies that produce simple ideas in us, viz. solidity, extension, motion or rest , nubmer or figure . These, which I call original or primary qualities of body, are wholly inseparable from it; and such as in all the alterations and changes it suffers, all the force can be used upon it, it constantly keeps; and such as sense constantly finds in every particle of matter which has bulk enough to be perceived; and the mind finds inseparable from every particle of matter, though less than to make itself singly be perceived by our senses: e.g., take a grain of wheat, divide it into two parts; each part has still solidity, extension, figure, and mobility: divide it again, and it retains still the same qualities …

(From II.viii.11— How Bodies produce Ideas in us ) The next thing to be considered is, how bodies operate one upon another; and that is manifestly by impulse, and nothing else. It being impossible to conceive that body should operate on what it does not touch (which is all one as to imagine it can operate where it is not), or when it does touch, operate any other way than by motion.

(From II.viii.13— How secondary Qualities produce their ideas ) After the same manner that the ideas of these original qualities are produced in us, we may conceive that the ideas of secondary qualities are also produced, viz. By the operation of insensible particles on our senses. … [L]et us suppose at present that, the different motions and figures, bulk and number, of such particles, affecting the several organs of our senses, produce in us those different sensations which we have from the colours and smells of bodies … It being no more impossible to conceive that god should annex such ideas to such motions, with which they have no similitude, than that he should annex the idea of pain to the motion of a piece of steel dividing our flesh, with which that idea hath no resemblance.

(From II.viii.14— They depend on the primary Qualities ) What I have said concerning colours and smells may be understood also of tastes and sounds, and other the like sensible qualities; which, whatever reality we by mistake attribute to them, are in truth nothing in the objects themselves, but powers to produce various sensations in us; and depend on those primary qualities, viz. Bulk, figure, texture, and motion of parts and therefore I call them secondary qualities .

(From II.viii.15— Ideas of primary Qualities are Resemblances; of secondary, not ) From whence I think it easy to draw this observation, that the ideas of primary qualities of bodies are resemblances of them, and their patterns do really exist in the bodies themselves, but the ideas produced in us by these secondary qualities have no resemblance of them at all. There is nothing like our ideas, existing in the bodies themselves. They are, in the bodies we denominate from them, only a power to produce those sensations in us …

(From II.viii.17— The ideas of the Primary alone really exist ) The particular bulk, number, figure, and motion of the parts of fire or snow are really in them, whether any one’s senses perceive them or no: and therefore they may be called real qualities, because they really exist in those bodies. But light, heat, whiteness, or coldness, are no more really in them than sickness or pain is in manna. Take away the sensation of them; let not the eyes see light or colours, nor the can hear sounds; let the palate not taste, nor the nose smell, and all colours, tastes, odours, and sounds, as they are such particular ideas , vanish and cease, and are reduced to their causes, i.e., bulk, figure, and motion of parts.

(From II.viii.19— Examples ) Let us consider the red and white colours in porphyry. Hinder light from striking on it, and its colours vanish; it no longer produces any such ideas in us: upon the return of light it produces these appearances on us again. Can any one think any real alterations are made in the porphyry by the presence or absence of light; and that those ideas of whiteness and redness are really in porphyry in the light, when it is plain it has no colour in the dark ? It has, indeed, such a configuration of particles, both night and day, as are apt, by the rays of light rebounding from some parts of that hard stone, to produce in us the idea of redness, and from others the idea of whiteness; but whiteness or redness are not in it at any time, but such a texture that hath the power to produce such a sensation in us.

(From II.viii.20) Pound an almond, and the clear white colour will be altered into a dirty one, and the sweet taste into an oily one. What real alteration can the beating of the pestle make in an body, but an alteration of the texture of it?

(From II.viii.21— Explains how water felt as cold by one hand may be warm to the other ) Ideas being thus distinguished and understood, we may be able to give an account how the same water, at the same time, may produce the idea of cold by one hand and of heat by the other: whereas it is impossible that the same water, if those ideas were really in it, should at the same time be both hot and cold. For, if we imagine warmth , as it is in our hands, to be nothing but a certain sort and degree of motion in the minute particles of our nerves or animal spirits, we may understand how it is possible that the same water may, at the same time, produce the sensations of heat in one hand and cold in the other; which yet figure never does, that never producing the idea of a square by one hand which has produced the idea of a globe by another.

Locke argues for three theses in this chapter:

• Ideas of secondary qualities do not resemble anything in the objects that ‘have’ them
• Secondary qualities depend on primary
• Secondary qualities are nothing but powers in objects to produce certain ideas in us

If there were no observers or perceivers, what would the world be like, according to Locke? That is, what qualities does a physical object have in itself?

How does Locke argue for his three theses? Let’s start with (i): ideas of secondary qualities resemble nothing in the objects.

Recall Aquinas’s picture of (bodily) causation: one object (e.g., fire) produces in another the same kind of quality it has in itself (e.g., heat). Why does Locke think that there isn’t really any heat in the first object? Let’s take a case where fire produces a sensation of heat in a person. If our sensation of heat resembled any quality in the object, that quality would have to be the cause of the heat that it produces.

• Why does Locke reject this? (see especially II.viii.11 above).
• Locke argues for a further thesis:

Why think that the color of an object (i.e., the color ideas it produces in us) depends on its primary qualities? (Hint: use II.viii.20)

Finally, what about thesis (iii): secondary qualities are nothing but powers in objects to produce certain ideas in us? Well, this is just to combine (i) and (ii). If they’re not resemblances, and they depend on the primary qualities, then to say that a body has a particular color is just to say that its parts are so arranged as to produce a given idea in us. (Note that primary qualities are powers and genuine qualities in objects; secondary are merely powers.)

• Think of as many different ways to change the color of this room as you can.

So far, we’ve dealt only with simple ideas. But our experience doesn’t seem to come to us packaged in simple, discrete elements. So Locke needs to deal with how we generate experiences (and thoughts) of ordinary objects—what he calls ‘substances’– out of simple ideas.

(From II.xii.1— Made by the Mind out of simple Ones ) We have hitherto considered those ideas, in the reception whereof the mind is only passive, which are those simple ones received from sensation and reflection before mentioned, whereof the mind cannot make one to itself, nor have any idea which does not wholly consist of them. … Ideas thus made up of several simple ones put together, I call complex .

(From II.xii.2— Made voluntarily ) In this faculty of repeating and joining together its ideas, the mind has great power in varying and multiplying the objects of its thoughts, infinitely beyond what sensation or reflection furnished it with: but all this still confined to those simple ideas which it received from those two sources, and which are the ultimate materials of all its compositions.

(From II.xii.3— Complex ideas are either of Modes, Substances, or Relations )

(From II.xxiii.1— Ideas of substances, how made ) The mind being, as I have declared, furnished with a great number of the simple ideas, conveyed in by the senses as they are found in exterior things, or by reflection on its own operations, takes notice also that a certain number of these simple ideas go constantly together; which being presumed to belong to one thing, and words being suited to common apprehensions, and made use of for quick dispatch are called, so united in one subject, by one name; which, by inadvertency, we are apt afterward to talk of and consider as one simple idea, which indeed is a complication of many ideas together: because, as I have said, not imagining how these simple ideas can subsist by themselves, we accustom ourselves to suppose some substratum wherein they do subsist, and from which they do result, which therefore we call substance .

• List the ideas necessary to construct an idea of a substance like Helga (a dog).

Our simple ideas represent qualities; to think of a substance like a dog, however, we need to think of these qualities as inhering in or being unified by some underlying substratum (which he sometimes also calls ‘pure substance in general’). What is Locke’s attitude toward this substratum, and our knowledge of it?

(From II.xiii.19— Substance and accidents of little use in Philosophy ) They who first ran into the notion of accidents , as a sort of real beings that needed something to inhere in, were forced to find out the word substance to support them. Had the poor Indian philosopher (who imagined that the earth also wanted something to bear it up) but thought of this word substance, he needed not to have been at the trouble to find an elephant to support it, and a tortoise to support his elephant: the word substance would have done it effectually. And he that inquired might have taken it for as good an answer from an Indian philosopher—that substance, without knowing what it is, is that which supports the earth, as take it for a sufficient answer and good doctrine from our european philosophers—that substance, without knowing what it is, is that which supports accidents. So that of substance, we have no idea of what it is, but only a confused obscure one of what it does.

(From II.xiii.20— Sticking on and under-propping ) Whatever a learned man may do here, an intelligent american, who inquired into the nature of things, would scarce take it for a satisfactory account, if, desiring to learn our architecture, he should be told that a pillar is a thing supported by a basis, and a basis something that supported a pillar. Would he not think himself mocked, instead of taught, with such an account as this? … Were the latin words, inhaerentia and substantio , put into the plain english ones that answer them, and were called sticking on and under-propping , they would better discover to us the very great clearness there is in the doctrine of substance and accidents, and show of what use they are in deciding of questions in philosophy.

(From II.xxiii.23— Our obscure Idea of Substance in general ) So that if any one will examine himself concerning his notion of pure substance in general, he will find he has no other idea of it at all, but only a supposition of he knows not what support of such qualities which are capable of producing simple ideas in us; which qualities are commonly called accidents. If any one should be asked, what is the subject wherein colour or weight inheres, he would have nothing to say, but the solid extended parts; and if he were demanded, what is it that solidity and extension adhere in, he would not be in a much better case than the Indian before mentioned who, saying that the world was supported by a great elephant, was asked what the elephant rested on; to which his answer was—a great tortoise: but being again pressed to know what gave support to the broad-backed tortoise, replied— something, he knew not what .

• It’s vital to see that by ‘substance’ Locke means here ‘substratum’: that in which properties inhere. This notion is akin to Aristotle’s notion of prime matter. Why might one say that Locke has a love/hate relationship with substratum?

Now that we know how we think about individual substances (e.g., an elephant), we need to know how we can think about kinds or sorts of things. I’m not limited to thinking (or talking) about individual substances; I can make claims that apply to groups or sorts of substances. Locke’s abstraction is the mechanism by which we move from purely determinate ideas to general ones.

Keep in mind that Locke has two kinds of fish to fry in this context: the Cartesians, who think that the essence of body is just extension, and the Aristotelians, who think that the world presents itself to us as if it were ‘carved at the joints’ into innumerable distinct natural kinds. In this context, Locke’s role as an ‘under-labourer’ to science is most in evidence.

(From III.ii.6— How general Words are made ) … Words become general by being made the signs of general ideas: and ideas become general, by separating from them the circumstances of time and place, and any other ideas that may determine them to this or that particular existence. By this way of abstraction they are made capable of representing more individuals than one; each of which having in it a conformity to that abstract idea, is (as we call it) of that sort.

(From III.ii.7— Shown by the way we enlarge our complex ideas from infancy ) … [T]here is nothing more evident, than that the ideas of the persons children converse with (to instance in them alone) are, like the persons themselves, only particular. The ideas of the nurse and the mother are well framed in their minds; and, like pictures of them there, represent only those individuals. The names they first gave to them are confined to these individuals; and the names of nurse and mamma , the child uses, determine themselves to those persons. Afterwards, when time and a larger acquaintance have made them observe that there are a great many other things in the world, that in some common agreements of shape, and several other qualities, resemble their father and mother, and those persons they have been used to, they frame an idea, which they find those many particulars do partake in; and to that they give, with others, the name man , for example. And thus they come to have a general name, and a general idea. Wherein they make nothing new; but only leave out of the complex idea they had of Peter and James, Mary and Jane, that which is peculiar to each, and retain only what is common to them all.

(From III.iii.11— General and Universal are Creatures of the Understanding, and belong not to the Real Existence of things ) [I]t is plain, by what has been said, that general and universal belong not to the real existence of things; but are the inventions and creatures of the understanding, made by it for its own use, and concern only signs, whether words or ideas. … [I]deas are general when they are set up as the representatives of many particular things: but universality belongs not to things themselves, which are all of them particular in their existence, even those words and ideas which in their signification are general. When therefore we quit particulars, the generals that rest are only creatures of our own making; their general nature being nothing but the capacity they are put into, by the understanding, of signifying or representing many particulars. For the signification they have is nothing but a relation that, by the mind of man, is added to them.

(From III.iii.13— They are the Workmanship of the Understanding, but have their Foundation in the Similitude of Things ) I would not here be thought to forget, much less to deny, that Nature, in the production of things, makes several of them alike: there is nothing more obvious, especially in the races of animals, and all things propagated by seed. But yet I think we may say, the sorting of them under names is the workmanship of the understanding, taking occasion, from the similitude it observes amongst them, to make abstract general ideas , and set them up in the mind, with names annexed to them, as patterns or forms, (for, in that sense, the word form has a very proper signification,) to which as particular things existing are found to agree, so they come to be of that species, have that denomination, or are put into that class .

(From III.iii.15— Several significations of the word Essence ) But since the essences of things are thought by some (and not without reason) to be wholly unknown, it may not be amiss to consider the several significations of the word essence .

Real essences . First, essence may be taken for the very being of anything, whereby it is what it is. And thus the real internal, but generally (in substances) unknown constitution of things, whereon their discoverable qualities depend, may be called their essence. This is the proper original signification of the word, as is evident from the formation of it; essential in its primary notation, signifying properly, being. And in this sense it is still used, when we speak of the essence of particular things, without giving them any name. Nominal essences . Secondly, the learning and disputes of the schools having been much busied about genus and species, the word essence has almost lost its primary signification: and, instead of the real constitution of things, has been almost wholly applied to the artificial constitution of genus and species. It is true, there is ordinarily supposed a real constitution of the sorts of things; and it is past doubt there must be some real constitution, on which any collection of simple ideas co-existing must depend. But, it being evident that things are ranked under names into sorts or species, only as they agree to certain abstract ideas, to which we have annexed those names, the essence of each genus , or sort, comes to be nothing but that abstract idea which the general, or sortal (if I may have leave so to call it from sort, as I do general from genus,) name stands for. And this we shall find to be that which the word essence imports in its most familiar use. These two sorts of essences, I suppose, may not unfitly be termed, the one the real , the other nominal essence .

(From III.iii.17— Supposition, that Species are distinguished by their real Essences useless ) [The opinion that considers] real essences as a certain number of forms or moulds, wherein all natural things that exist are cast, and do equally partake, has, I imagine, very much perplexed the knowledge of natural things. The frequent productions of monsters, in all the species of animals, and of changelings, and other strange issues of human birth, carry with them difficulties, not possible to consist with this hypothesis; since it is as impossible that two things partaking exactly of the same real essence should have different properties, as that two figures partaking of the same real essence of a circle should have different properties. But were there no other reason against it, yet the supposition of essences that cannot be known; and the making of them, nevertheless, to be that which distinguishes the species of things, is so wholly useless and unserviceable to any part of our knowledge, that that alone were sufficient to make us lay it by …

(From III.vi.6— Even the real essences of individual substances imply potential sorts ) It is true, I have often mentioned a real essence , distinct in substances from those abstract ideas of them, which I call their nominal essence. By this real essence I mean, that real constitution of anything, which is the foundation of all those properties that are combined in, and are constantly found to co-exist with the nominal essence; that particular constitution which everything has within itself, without any relation to anything without it. But essence, even in this sense, relates to a sort, and supposes a species . For, being that real constitution on which the properties depend, it necessarily supposes a sort of things, properties belonging only to species, and not to individuals: e.g., supposing the nominal essence of gold to be a body of such a peculiar colour and weight, with malleability and fusibility, the real essence is that constitution of the parts of matter on which these qualities and their union depend; and is also the foundation of its solubility in aqua regia and other properties, accompanying that complex idea. Hre are essences and properties, but all upon supposition of a sort or general abstract idea, which is considered as immutable; but there is no individual parcel of matter to which any of these qualities are so annexed as to be essential to it or inseparable from it.

(From III.vi.50) For, let us consider, when we affirm that ‘all gold is fixed,’ either it means that fixedness is a part of the definition, i.e., part of the nominal essence the word ‘gold’ stands for; and so this affirmation, ‘all gold is fixed,’ contains nothing but the signification of the term ‘gold’.

Or else it means, that fixedness, not being a part of the definition of ‘gold’, is a property of that substance itself: in which case it is plain that the word ‘gold’ stands in the place of a substance, having the real essence of a species of things made by nature. In which way of substitution it has so confused and uncertain a signification, that, though this proposition—‘gold is fixed’—be in that sense an affirmation of something real; yet it is a truth will always fail us in its particular application, and so is of no real use or certainty. For let it be ever so true, that all gold, i.e., all that has the real essence of gold, is fixed, what serves this for, whilst we know not, in this sense, what is or is not gold? For if we know not the real essence of gold, it is impossible we should know what parcel of matter has that essence, and so whether it be true gold or no.

• In this passage, Locke argues that all general claims about kinds (e.g., ‘gold is fixed’) are either trivial or uncertain. Using the gold example, explain each of these alternatives. In what way can it be taken as trivial? As uncertain?

Now that we have some story about how our ideas of substances are constructed, we need to look at the two main kinds of substance we seem to find in the world: mind and body. Notice Locke’s argument against Descartes’s conflation of body and extension. Locke also replies here to Leibniz’s argument against Newtonian space, namely, that it must be either a substance or an accident, and neither makes much sense.

(From II.xiii.17— Cohesion of solid parts and Impulse, the primary ideas peculiar to Body ) The primary ideas we have peculiar to body , as contradistinguished to spirit, are the cohesion of solid, and consequently separable, parts , and a power of communicating motion by impulse . These, I think, are the original ideas proper and peculiar to body; for figure is but the consequence of finite extension.

(From II.xiii.11— Extension and Body not the same ) There are some that would persuade us, that body and extension are the same thing … If, therefore, they mean by body and extension the same that other people do, viz. By body something that is solid and extended, whose parts are separable and movable different ways; and by extension , only the space that lies between the extremities of those solid coherent parts, and which is possessed by them, [then] they confound very different ideas one with another; for I appeal to every man’s own thoughts, whether the idea of space be not as distinct from that of solidity, as it is from the idea of scarlet colour? It is true, solidity cannot exist without extension, neither can scarlet colour exist without extension, but this hinders not, but that they are distinct ideas.

And if it be a reason to prove that spirit is different from body, because thinking includes not the idea of extension in it; the same reason will be as valid, I suppose, to prove that space is not body, because it includes not the idea of solidity in it; space and solidity being as distinct ideas as thinking and extension , and as wholly separable in the mind one from another … Extension includes no solidity, nor resistance to the motion of body, as body does.

(From II.xiii.3— Space and Extension ) This space, considered barely in length between any two beings, without considering anything else between them, is called distance : if considered in length, breadth, and thickness, I think it may be called capacity . When considered between the extremities of matter, which fills the capacity of space with something solid, tangible, and moveable, it is properly called extension . And so extension is an idea belonging to body only; but space may, as is evident, be considered without it.

(From II.xiii.17— Substance, which we know not, no proof against space without body ) If it be demanded (as usually it is) whether this space, void of body, be substance or accident , I shall readily answer I know not; nor shall be ashamed to own my ignorance, till they that ask show me a clear distinct idea of substance.

Locke here sets out the constituent ideas that make up the complex idea of the mind. He also launches an attack against Descartes’s claim that thought is the essence of the soul. Most famously, he denies that we can be sure that what thinks in us in an immaterial substance.

(From II.xxiii.18. Thinking and motivity ) The ideas we have belonging and peculiar to spirit , are thinking , and will , or a power of putting body into motion by thought, and, which is consequent to it, liberty . For, as body cannot but communicate its motion by impulse to another body, which it meets with at rest, so the mind can put bodies into motion, or forbear to do so, as it pleases. The ideas of existence , duration , and mobility , are common to them both.

(From II.i.10— The Soul thinks not always; for this wants Proofs ) … I confess myself to have one of those dull souls, that doth not perceive itself always to contemplate ideas; nor can conceive it any more necessary for the soul always to think, than for the body always to move: the perception of ideas being (as I conceive) to the soul, what motion is to the body; not its essence, but one of its operations. And therefore, though thinking be supposed never so much the proper action of the soul, yet it is not necessary to suppose that it should be always thinking, always in action. … To say that actual thinking is essential to the soul, and inseparable from it, is to beg what is in question, and not to prove it by reason; which is necessary to be done, if it be not a self-evident proposition But whether this, “That the soul always thinks,” be a self-evident proposition, that everybody assents to at first hearing, I appeal to mankind. It is doubted whether I thought at all last night or no. The question being about a matter of fact, it is begging it to bring, as a proof for it, an hypothesis, which is the very thing in dispute: by which way one may prove anything …

But men in love with their opinions may not only suppose what is in question, but allege wrong matter of fact. How else could any one make it an inference of mine, that a thing is not, because we are not sensible of it in our sleep? I do not say there is no soul in a man, because he is not sensible of it in his sleep; but I do say, he cannot think at any time, waking or sleeping, without being sensible of it. Our being sensible of it is not necessary to anything but to our thoughts; and to them it is; and to them it always will be necessary, till we can think without being conscious of it.

• Locke begins with an argument from experience. How does it work? We can think of it as a reductio ad absurdum :

Premise 1: The soul’s essence is to think (Descartes’s view) Premise 2: Given 1, it follows that the soul _______ (since this is part of what it is to be an essential property) Premise 3: But experience shows _______. Conclusion: _______.

Now, Locke realizes that the Cartesian will not leave things at that; he will insist that minds think even during sleep, though they do not remember it. Locke thinks this move has a heavy price:

(From II.i.11— It is not always conscious of [thinking] ) I grant that the soul, in a waking man, is never without thought, because it is the condition of being awake. But whether sleeping without dreaming be not an affection of the whole man, mind as well as body, may be worth a waking man’s consideration; it being hard to conceive that anything should think and not be conscious of it. If the soul doth think in a sleeping man without being conscious of it, I ask whether, during such thinking, it has any pleasure or pain, or be capable of happiness or misery? I am sure the man is not; no more than the bed or earth he lies on. For to be happy or miserable without being conscious of it, seems to me utterly inconsistent and impossible. Or if it be possible that the soul can, whilst the body is sleeping, have its thinking, enjoyments, and concerns, its pleasures or pain, apart, which the man is not conscious of nor partakes in—it is certain that Socrates asleep and Socrates awake is not the same person; but his soul when he sleeps, and Socrates the man, consisting of body and soul, when he is waking, are two persons: since waking Socrates has no knowledge of, or concernment for that happiness or misery of his soul, which it enjoys alone by itself whilst he sleeps, without perceiving anything of it; no more than he has for the happiness or misery of a man in the indies, whom he knows not. For, if we take wholly away all consciousness of our actions and sensations, especially of pleasure and pain, and the concernment that accompanies it, it will be hard to know wherein to place personal identity.

• What price does Locke think Descartes must pay, in order to hang on to his claim that the soul always thinks?

(From II.xxiii.5— As clear an idea of spiritual substance as of corporeal substance ) The same thing happens concerning the operations of the mind, viz. thinking, reasoning, fearing, &c., which we concluding not to subsist of themselves, nor apprehending how they can belong to body, or be produced by it, we are apt to think these the actions of some other substance , which we call spirit ; whereby yet it is evident that, having no other idea or notion of matter, but something wherein those many sensible qualities which affect our senses do subsist; by supposing a substance wherein thinking, knowing, doubting, and a power of moving, &c., do subsist, we have as clear a notion of the substance of spirit, as we have of body; the one being supposed to be (without knowing what it is) the substratum to those simple ideas we have from without; and the other supposed (with a like ignorance of what it is) to be the substratum to those operations we experiment in ourselves within. It is plain then, that the idea of corporeal substance in matter is as remote from our conceptions and apprehensions, as that of spiritual substance , or spirit: and therefore, from our not having, any notion of the substance of spirit, we can no more conclude its non-existence, than we can, for the same reason, deny the existence of body …

(From II.xxiii.16— No Idea of abstract Substance either in Body or Spirit ) By the complex idea of extended, figured, coloured, and all other sensible qualities, which is all that we know of it, we are as far from the idea of the substance of body, as if we knew nothing at all: nor after all the acquaintance and familiarity which we imagine we have with matter, and the many qualities men assure themselves they perceive and know in bodies, will it perhaps upon examination be found, that they have any more or clearer primary ideas belonging to body, than they have belonging to immaterial spirit.

(From II.xxiii.23— Cohesion of solid Parts in Body as hard to be conceived as thinking in a Soul ) [I]f [a man] says he knows not how he thinks, I answer, Neither knows he how he is extended, how the solid parts of body are united or cohere together to make extension. For though the pressure of the particles of air may account for the cohesion of several parts of matter that are grosser than the particles of air, and have pores less than the corpuscles of air, yet the weight or pressure of the air will not explain, nor can be a cause of the coherence of the particles of air themselves. And if the pressure of the aether, or any subtiler matter than the air, may unite, and hold fast together, the parts of a particle of air, as well as other bodies, yet it cannot make bonds for itself , and hold together the parts that make up every the least corpuscle of that materia subtilis .

(From II.xxiii.28— Communication of Motion by Impulse, or by Thought, equally unintelligible ) Another idea we have of body is, the power of communication of motion by impulse ; and of our souls, the power of exciting motion by thought . These ideas, the one of body, the other of our minds, every day’s experience clearly furnishes us with: but if here again we inquire how this is done, we are equally in the dark. For, in the communication of motion by impulse, wherein as much motion is lost to one body as is got to the other, which is the ordinariest case, we can have no other conception, but of the passing of motion out of one body into another; which, I think, is as obscure and inconceivable as how our minds move or stop our bodies by thought, which we every moment find they do. We have by daily experience clear evidence of motion produced both by impulse and by thought; but the manner how, hardly comes within our comprehension: we are equally at a loss in both. So that, however we consider motion, and its communication, either from body or spirit, the idea which belongs to spirit is at least as clear as that which belongs to body. And if we consider the active power of moving, or, as I may call it, motivity, it is much clearer in spirit than body; since two bodies, placed by one another at rest, will never afford us the idea of a power in the one to move the other, but by a borrowed motion. …

• Locke is here raising the problem of transference: how can one body give its motion to another? See Aquinas , Summa Contra Gentiles Chapter Sixty-nine, Section Seven , and Descartes’s Principles (Part II, sections xxiv-v). How would each react to what Locke says here?

(From IV.iii.6— Our Knowledge, therefore narrower than our Ideas ) From all which it is evident, that the extent of our knowledge comes not only short of the reality of things, but even of the extent of our own ideas. Though our knowledge be limited to our ideas, and cannot exceed them either in extent or perfection; … Yet it would be well with us if our knowledge were but as large as our ideas, and there were not many doubts and inquiries concerning the ideas we have , whereof we are not, nor I believe ever shall be in this world resolved. Nevertheless, I do not question but that human knowledge, under the present circumstances of our beings and constitutions, may be carried much further than it has hitherto been, if men would sincerely, and with freedom of mind, employ all that industry and labour of thought, in improving the means of discovering truth, which they do for the colouring or support of falsehood, to maintain a system, interest, or party they are once engaged in.

… We have the ideas of a square , a circle , and equality ; and yet, perhaps, shall never be able to find a circle equal to a square, and certainly know that it is so. We have the ideas of matter and thinking , but possibly shall never be able to know whether [any mere material being] thinks or no; it being impossible for us, by the contemplation of our own ideas, without revelation, to discover whether Omnipotency has not given to some systems of matter, fitly disposed, a power to perceive and think, or else joined and fixed to matter, so disposed, a thinking immaterial substance: it being, in respect of our notions, not much more remote from our comprehension to conceive that God can, if he pleases, superadd to matter a faculty of thinking , than that he should superadd to it another substance with a faculty of thinking ; since we know not wherein thinking consists, nor to what sort of substances the Almighty has been pleased to give that power, which cannot be in any created being, but merely by the good pleasure and bounty of the Creator. For I see no contradiction in it, that the first Eternal thinking Being, or Omnipotent Spirit, should, if he pleased, give to certain systems of created senseless matter, put together as he thinks fit, some degrees of sense, perception, and thought: though, as I think I have proved, lib. iv. Ch. 10, Section 14, &c., it is no less than a contradiction to suppose matter (which is evidently in its own nature void of sense and thought) should be that Eternal first-thinking Being. What certainty of knowledge can any one have, that some perceptions, such as, e.g., pleasure and pain, should not be in some bodies themselves, after a certain manner modified and moved, as well as that they should be in an immaterial substance, upon the motion of the parts of body: Body, as far as we can conceive, being able only to strike and affect body, and motion, according to the utmost reach of our ideas, being able to produce nothing but motion; so that when we allow it to produce pleasure or pain, or the idea of a colour or sound, we are fain to quit our reason, go beyond our ideas, and attribute it wholly to the good pleasure of our Maker. For, since we must allow He has annexed effects to motion which we can no way conceive motion able to produce, what reason have we to conclude that He could not order them as well to be produced in a subject we cannot conceive capable of them, as well as in a subject we cannot conceive the motion of matter can any way operate upon? I say not this, that I would any way lessen the belief of the soul’s immateriality: I am not here speaking of probability, but knowledge, and I think not only that it becomes the modesty of philosophy not to pronounce magisterially, where we want that evidence that can produce knowledge; but also, that it is of use to us to discern how far our knowledge does reach; for the state we are at present in, not being that of vision, we must in many things content ourselves with faith and probability: and in the present question, about the Immateriality of the Soul, if our faculties cannot arrive at demonstrative certainty, we need not think it strange. All the great ends of morality and religion are well enough secured, without philosophical proofs of the soul’s immateriality … since it is evident, that he who made us at the beginning to subsist here, sensible intelligent beings, and for several years continued us in such a state, can and will restore us to the like state of sensibility in another world, and make us capable there to receive the retribution he has designed to men, according to their doings in this life.

And therefore it is not of such mighty necessity to determine one way or the other, as some, over-zealous for or against the immateriality of the soul, have been forward to make the world believe. Who, either on the one side, indulging too much their thoughts immersed altogether in matter, can allow no existence to what is not material: or who, on the other side, finding not cogitation within the natural powers of matter, examined over and over again by the utmost intention of mind, have the confidence to conclude—that Omnipotency itself cannot give perception and thought to a substance which has the modification of solidity. He that considers how hardly sensation is, in our thoughts, reconcilable to extended matter; or existence to anything that has no extension at all, will confess that he is very far from certainly knowing what his soul is. It is a point which seems to me to be put out of the reach of our knowledge: and he who will give himself leave to consider freely, and look into the dark and intricate part of each hypothesis, will scarce find his reason able to determine him fixedly for or against the soul’s materiality. Since, on which side soever he views it, either as an unextended substance , or as a thinking extended matter , the difficulty to conceive either will, whilst either alone is in his thoughts, still drive him to the contrary side. …

It is past controversy, that we have in us something that thinks; our very doubts about what it is, confirm the certainty of its being, though we must content ourselves in the ignorance of what kind of being it is: and it is in vain to go about to be sceptical in this, as it is unreasonable in most other cases to be positive against the being of anything, because we cannot comprehend its nature. For I would fain know what substance exists, that has not something in it which manifestly baffles our understandings …

Can Locke make good on his claim that ‘all the great ends of religion and morality’ can be served, even without a proof of the soul’s immortality? Both religion and morality require, Locke thinks, the certainty of post-mortem rewards and harms. But how can we make sense of the self surviving the death of the body, if we cannot show that the self is immaterial?

(From II.xxvii.8— Idea of identity suited to the idea it is applied to ) It is not therefore unity of substance that comprehends all sorts of identity, or will determine it in every case; but to conceive and judge of it aright, we must consider what idea the word it is applied to stands for: it being one thing to be the same substance , another the same man , and a third the same person , if person , man , and substance , are three names standing for three different ideas;—for such as is the idea belonging to that name, such must be the identity; which, if it had been a little more carefully attended to, would possibly have prevented a great deal of that confusion which often occurs about this matter, with no small seeming difficulties, especially concerning personal identity, which therefore we shall in the next place a little consider.

(From II.xxvii.4) [L]et us suppose an atom, i.e., a continued body under one immutable superficies, existing in a determined time and place; it is evident, that, considered in any instant of its existence, it is in that instant the same with itself. For, being at that instant what it is, and nothing else, it is the same, and so must continue as long as its existence is continued; for so long it will be the same, and no other. In like manner, if two or more atoms be joined together into the same mass, every one of those atoms will be the same, by the foregoing rule: and whilst they exist united together, the mass, consisting of the same atoms, must be the same mass, or the same body, let the parts be ever so differently jumbled. But if one of these atoms be taken away, or one new one added, it is no longer the same mass or the same body. In the state of living creatures, their identity depends not on a mass of the same particles, but on something else. For in them the variation of great parcels of matter alters not the identity: an oak growing from a plant to a great tree, and then lopped, is still the same oak; and a colt grown up to a horse, sometimes fat, sometimes lean, is all the while the same horse: though, in both these cases, there may be a manifest change of the parts; so that truly they are not either of them the same masses of matter, though they be truly one of them the same oak, and the other the same horse. The reason whereof is, that, in these two cases—a mass of matter and a living body —identity is not applied to the same thing.

(From II.xxvii.5– Identity of Vegetables ) We must therefore consider wherein an oak differs from a mass of matter, and that seems to me to be in this, that the one is only the cohesion of particles of matter any how united, the other such a disposition of them as constitutes the parts of an oak; and such an organization of those parts as is fit to receive and distribute nourishment, so as to continue and frame the wood, bark, and leaves, &c., of an oak, in which consists the vegetable life. That being then one plant which has such an organization of parts in one coherent body, partaking of one common life, it continues to be the same plant as long as it partakes of the same life, though that life be communicated to new particles of matter vitally united to the living plant, in a like continued organization conformable to that sort of plants. For this organization, being at any one instant in any one collection of matter, is in that particular concrete distinguished from all other, and is that individual life, which existing constantly from that moment both forwards and backwards, in the same continuity of insensibly succeeding parts united to the living body of the plant, it has that identity which makes the same plant, and all the parts of it, parts of the same plant, during all the time that they exist united in that continued organization, which is fit to convey that common life to all the parts so united.

(From II.xxvii.6– Identity of Animals ) The case is not so much different in brutes but that any one may hence see what makes an animal and continues it the same. Something we have like this in machines, and may serve to illustrate it. For example, what is a watch? it is plain it is nothing but a fit organization or construction of parts to a certain end, which, when a sufficient force is added to it, it is capable to attain. If we would suppose this machine one continued body, all whose organized parts were repaired, increased, or diminished by a constant addition or separation of insensible parts, with one common life, we should have something very much like the body of an animal …

(From II.xxvii.7— The Identity of Man ) This also shows wherein the identity of the same man consists; viz. in nothing but a participation of the same continued life, by constantly fleeting particles of matter, in succession vitally united to the same organized body.

(From II.xxvii.11— Personal Identity ) This being premised, to find wherein personal identity consists, we must consider what person stands for; which, I think, is a thinking intelligent being, that has reason and reflection, and can consider itself as itself, the same thinking thing, in different times and places; which it does only by that consciousness which is inseparable from thinking, and, as it seems to me, essential to it: it being impossible for any one to perceive without perceiving that he does perceive. When we see, hear, smell, taste, feel, meditate, or will anything, we know that we do so. Thus it is always as to our present sensations and perceptions: and by this every one is to himself that which he calls self —it not being considered, in this case, whether the same self be continued in the same or divers substances. For, since consciousness always accompanies thinking, and it is that which makes every one to be what he calls self, and thereby distinguishes himself from all other thinking things, in this alone consists personal identity, i.e., the sameness of a rational being: and as far as this consciousness can be extended backwards to any past action or thought, so far reaches the identity of that person; it is the same self now it was then; and it is by the same self with this present one that now reflects on it, that that action was done.

(From II.xxvii.12— Consciousness makes personal Identity ) But it is further inquired, whether it be the same identical substance. This few would think they had reason to doubt of, if these perceptions, with their consciousness, always remained present in the mind, whereby the same thinking thing would be always consciously present, and, as would be thought, evidently the same to itself. But that which seems to make the difficulty is this, that this consciousness being interrupted always by forgetfulness, there being no moment of our lives wherein we have the whole train of all our past actions before our eyes in one view, but even the best memories losing the sight of one part whilst they are viewing another; and we sometimes, and that the greatest part of our lives, not reflecting on our past selves, being intent on our present thoughts, and in sound sleep having no thoughts at all, or at least none with that consciousness which remarks our waking thoughts—I say, in all these cases, our consciousness being interrupted, and we losing the sight of our past selves, doubts are raised whether we are the same thinking thing, i.e., the same substance or no. Which, however reasonable or unreasonable, concerns not personal identity at all. … For as far as any intelligent being can repeat the idea of any past action with the same consciousness it had of it at first, and with the same consciousness it has of any present action; so far it is the same personal self. For it is by the consciousness it has of its present thoughts and actions, that it is self to itself now, and so will be the same self, as far as the same consciousness can extend to actions past or to come; and would be by distance of time, or change of substance, no more two persons, than a man be two men by wearing other clothes to-day than he did yesterday, with a long or a short sleep between: the same consciousness uniting those distant actions into the same person, whatever substances contributed to their production.

(From II.xxvii.14— Personality in Change of Substance ) But the question is, Whether if the same substance which thinks be changed, it can be the same person; or, remaining the same, it can be different persons? And to this I answer: First, This can be no question at all to those who place thought in a purely material animal constitution, void of an immaterial substance. For, whether their supposition be true or no, it is plain they conceive personal identity preserved in something else than identity of substance; as animal identity is preserved in identity of life, and not of substance. And therefore those who place thinking in an immaterial substance only, before they can come to deal with these men, must show why personal identity cannot be preserved in the change of immaterial substances, or variety of particular immaterial substances, as well as animal identity is preserved in the change of material substances, or variety of particular bodies …

(From II.xxvii.15— Whether in Change of thinking Substances there can be one Person ) [I]t must be allowed, that, if the same consciousness (which, as has been shown, is quite a different thing from the same numerical figure or motion in body) can be transferred from one thinking substance to another, it will be possible that two thinking substances may make but one person. For the same consciousness being preserved, whether in the same or different substances, the personal identity is preserved.

(From II.xxvii.17— The body, as well as the soul, goes to the making of a Man ) And thus may we be able, without any difficulty, to conceive the same person at the resurrection, though in a body not exactly in make or parts the same which he had here, the same consciousness going along with the soul that inhabits it. But yet the soul alone, in the change of bodies, would scarce to any one but to him that makes the soul the man, be enough to make the same man. For should the soul of a prince, carrying with it the consciousness of the prince’s past life, enter and inform the body of a cobbler, as soon as deserted by his own soul, every one sees he would be the same person with the prince, accountable only for the prince’s actions: but who would say it was the same man ?

(From II.xxvii.19— Self depends on Consciousness, not on Substance ) Self is that conscious thinking thing—whatever substance made up of (whether spiritual or material, simple or compounded, it matters not)—which is sensible or conscious of pleasure and pain, capable of happiness or misery, and so is concerned for itself, as far as that consciousness extends.

(From II.xxvii.20— Persons, not Substances, the Objects of Reward and Punishment ) In this personal identity is founded all the right and justice of reward and punishment; happiness and misery being that for which every one is concerned for himself , and not mattering what becomes of any substance , not joined to, or affected with that consciousness.

(From II.xxvii.21— Which shows wherein Personal identity consists ) This may show us wherein personal identity consists: not in the identity of substance, but, as I have said, in the identity of consciousness … if Socrates waking and sleeping do not partake of the same consciousness, Socrates waking and sleeping is not the same person. And to punish Socrates waking for what sleeping Socrates thought, and waking Socrates was never conscious of, would be no more of right, than to punish one twin for what his brother-twin did, whereof he knew nothing, because their outsides were so like, that they could not be distinguished; for such twins have been seen.

(From II.xxvii.24— Objection ) But is not a man drunk and sober the same person? Why else is he punished for the fact he commits when drunk, though he be never afterwards conscious of it? Just as much the same person as a man that walks, and does other things in his sleep, is the same person, and is answerable for any mischief he shall do in it. Human laws punish both, with a justice suitable to their way of knowledge; because, in these cases, they cannot distinguish certainly what is real, what counterfeit: and so the ignorance in drunkenness or sleep is not admitted as a plea. But in the great day, wherein the secrets of all hearts shall be laid open, it may be reasonable to think, no one shall be made to answer for what he knows nothing of; but shall receive his doom, his conscience accusing or excusing him.

• What is Locke’s sortal relativity thesis?
• Atom over time?
• Mass of atoms?
• What does Descartes think accounts for personal identity over time?
• What does Locke think is wrong with Descartes’s answer?

It now makes sense to turn to Locke’s official discussion of the limits of knowledge. Keep in mind that the two orders of classification Locke introduces (manners or degrees of knowledge and the objects known) cut across each other. I’ve chosen to frame the discussion in terms of the objects of knowledge: identity (known by intuition), relation (by demonstration), co-existence, and real existence (by sensation).

(From IV.i.1— Our Knowledge conversant about our Ideas only ) Since the mind, in all its thoughts and reasonings, hath no other immediate object but its own ideas, which it alone does or can contemplate, it is evident that our knowledge is only conversant about them.

(From IV.i.2— Knowledge is the perception of the agreement or disagreement of two ideas ) Knowledge then seems to me to be nothing but the perception of the connexion of and agreement, or disagreement and repugnancy of any of our ideas . In this alone it consists. Where this perception is, there is knowledge, and where it is not, there, though we may fancy, guess, or believe, yet we always come short of knowledge. For when we know that white is not black, what do we else but perceive, that these two ideas do not agree? when we possess ourselves with the utmost security of the demonstration, that the three angles of a triangle are equal to two right ones, what do we more but perceive, that equality to two right ones does necessarily agree to, and is inseparable from, the three angles of a triangle?

(From IV.i.3— This Agreement or Disagreement may be any of four sorts ) But to understand a little more distinctly wherein this agreement or disagreement consists, I think we may reduce it all to these four sorts: i. identity , or diversity . ii. relation . iii. co-existence , or necessary connexion . iv. real existence .

(From IV.i.4— First, of Identity, or Diversity in ideas ) First , as to the first sort of agreement or disagreement, viz. identity or diversity . It is the first act of the mind, when it has any sentiments or ideas at all, to perceive its ideas; and so far as it perceives them, to know each what it is, and thereby also to perceive their difference, and that one is not another.

(From IV.i.5— Secondly, of abstract Relations between ideas ) Secondly , the next sort of agreement or disagreement the mind perceives in any of its ideas may, I think, be called relative , and is nothing but the perception of the relation between any two ideas, of what kind soever, whether substances, modes, or any other.

(From IV.i.6— Thirdly, of their necessary Co-existence in Substances ) The third sort of agreement or disagreement to be found in our ideas, which the perception of the mind is employed about, is co-existence or non-co-existence in the same subject ; and this belongs particularly to substances. Thus when we pronounce concerning gold, that it is fixed, our knowledge of this truth amounts to no more but this, that fixedness, or a power to remain in the fire unconsumed, is an idea that always accompanies and is joined with that particular sort of yellowness, weight, fusibility, malleableness, and solubility in aqua regia , which make our complex idea signified by the word ‘gold’.

(From IV.iii.9– Of their Co-existence, extends only a very little way ) [A]s to the … agreement or disagreement of our ideas in co-existence , in this our knowledge is very short; though in this consists the greatest and most material part of our knowledge concerning substances. For our ideas of the species of substances being, as I have showed, nothing but certain collections of simple ideas united in one subject, and so co-existing together; e.g., our idea of flame is a body hot, luminous, and moving upward; of gold, a body heavy to a certain degree, yellow, malleable, and fusible: for these, or some such complex ideas as these, in men’s minds, do these two names of the different substances, flame and gold, stand for. When we would know anything further concerning these, or any other sort of substances, what do we inquire, but what other qualities or powers these substances have or have not? which is nothing else but to know what other simple ideas do, or do not co-exist with those that make up that complex idea?

(From IV.iii.10— Because the Connexion between simple Ideas in substances is for the most part unknown ) This, how weighty and considerable a part soever of human science, is yet very narrow, and scarce any at all. The reason whereof is, that the simple ideas whereof our complex ideas of substances are made up are, for the most part, such as carry with them, in their own nature, no visible necessary connexion or inconsistency with any other simple ideas, whose co-existence with them we would inform ourselves about.

(From IV.iii.25) If a great, nay, far the greatest part of the several ranks of bodies in the universe escape our notice by their remoteness, there are others that are no less concealed from us by their minuteness. These insensible corpuscles , being the active parts of matter, and the great instruments of nature, on which depend not only all their secondary qualities, but also most of their natural operations, our want of precise distinct ideas of their primary qualities keeps us in an incurable ignorance of what we desire to know about them.

I doubt not but if we could discover the figure, size, texture, and motion of the minute constituent parts of any two bodies, we should know without trial several of their operations one upon another; as we do now the properties of a square or a triangle. Did we know the mechanical affections of the particles of rhubarb, hemlock, opium, and a man, as a watchmaker does those of a watch, whereby it performs its operations; and of a file, which by rubbing on them will alter the figure of any of the wheels; we should be able to tell beforehand that rhubarb will purge, hemlock kill, and opium make a man sleep: as well as a watchmaker can, that a little piece of paper laid on the balance will keep the watch from going till it be removed; or that, some small part of it being rubbed by a file, the machine would quite lose its motion, and the watch go no more. The dissolving of silver in aqua fortis , and gold in aqua regia , and not vice versa , would be then perhaps no more difficult to know than it is to a smith to understand why the turning of one key will open a lock, and not the turning of another. But whilst we are destitute of senses acute enough to discover the minute particles of bodies, and to give us ideas of their mechanical affections, we must be content to be ignorant of their properties and ways of operation; nor can we be assured about them any further than some few trials we make are able to reach. But whether they will succeed again another time, we cannot be certain. This hinders our certain knowledge of universal truths concerning natural bodies: and our reason carries us herein very little beyond particular matter of fact.

(From IV.vi.9— No discoverable necessary connexion between nominal essence gold, and other simple ideas ) As there is no discoverable connexion between fixedness and the colour, weight, and other simple ideas of that nominal essence of gold; so, if we make our complex idea of gold, a body yellow, fusable, ductile, weighty, and fixed, we shall be at the same uncertainty concerning solubility in aqua regia , and for the same reason. Since we can never, from consideration of the ideas themselves, with certainty affirm or deny of a body whose complex idea is made up of yellow, very weighty, ductile, fusible, and fixed, that it is soluble in aqua regia : and so on of the rest of its qualities. I would gladly meet with one general affirmation concerning any will, no doubt, be presently objected, is not this an universal proposition, “all gold is malleable” ? to which I answer, it is a very complex idea the word ‘gold’ stands for. But then here is nothing affirmed of gold, but that that sound stands for an idea in which malleableness is contained: and such a sort of truth and certainty as this it is, to say a centaur is four-footed. But if malleableness make not a part of the specific essence the name of ‘gold’ stands for, it is plain, “all gold is malleable” , is not a certain proposition. Because, let the complex idea of gold be made up of whichsoever of its other qualities you please, malleableness will not appear to depend on that complex idea, nor follow from any simple one contained in it: the connexion that malleableness has (if it has any) with those other qualities being only by the intervention of the real constitution of its insensible parts; which, since we know not, it is impossible we should perceive that connexion, unless we could discover that which ties them together.

(From IV.i.7— Fourthly, of real Existence agreeing to any idea ) The fourth and last sort is that of actual real existence agreeing to any idea.

(From IV.ii.1— Of the degrees, or differences in clearness, of our Knowledge )

• Intuitive: The different clearness of our knowledge seems to me to lie in the different way of perception the mind has of the agreement or disagreement of any of its ideas. For if we will reflect on our own ways of thinking, we will find, that sometimes the mind perceives the agreement or disagreement of two ideas immediately by themselves , without the intervention of any other: and this I think we may call intuitive knowledge .

(From IV.ii.2)

• Demonstrative: The next degree of knowledge is, where the mind perceives the agreement or disagreement of any ideas, but not immediately. Though wherever the mind perceives the agreement or disagreement of any of its ideas, there be certain knowledge; yet it does not always happen, that the mind sees that agreement or disagreement, which there is between them, even where it is discoverable; and in that case remains in ignorance, and at most gets no further than a probable conjecture. … In this case then, when the mind cannot so bring its ideas together as by their immediate comparison, and as it were juxta-position or application one to another, to perceive their agreement or disagreement, it is fain, by the intervention of other ideas , (one or more, as it happens) to discover the agreement or disagreement which it searches; and this is that which we call reasoning . …

(From IV.ii.14)

• Sensitive knowledge of the particular existence of finite beings without us. These two, viz. intuition and demonstration, are the degrees of our knowledge ; whatever comes short of one of these, with what assurance soever embraced, is but faith or opinion , but not knowledge, at least in all general truths. There is, indeed, another perception of the mind, employed about the particular existence of finite beings without us, which, going beyond bare probability, and yet not reaching perfectly to either of the foregoing degrees of certainty, passes under the name of knowledge . There can be nothing more certain than that the idea we receive from an external object is in our minds: this is intuitive knowledge. But whether there be anything more than barely that idea in our minds; whether we can thence certainly infer the existence of anything without us, which corresponds to that idea, is that whereof some men think there may be a question made; because men may have such ideas in their minds, when no such thing exists, no such object affects their senses. But yet here I think we are provided with an evidence that puts us past doubting. For I ask any one, whether he be not invincibly conscious to himself of a different perception, when he looks on the sun by day, and thinks on it by night; when he actually tastes wormwood, or smells a rose, or only thinks on that savour or odour? We as plainly find the difference there is between any idea revived in our minds by our own memory, and actually coming into our minds by our senses, as we do between any two distinct ideas. If any one say, a dream may do the same thing, and all these ideas may be produced, in us without any external objects; he may please to dream that I make him this answer:

That it is no great matter, whether I remove his scruple or no: where all is but dream, reasoning and arguments are of no use, truth and knowledge nothing. That I believe he will allow a very manifest difference between dreaming of being in the fire, and being actually in it. But yet if he be resolved to appear so sceptical as to maintain, that what I call being actually in the fire is nothing but a dream; and that we cannot thereby certainly know, that any such thing as fire actually exists without us: I answer, that we certainly finding that pleasure or pain follows upon the application of certain objects to us, whose existence we perceive, or dream that we perceive, by our senses; this certainty is as great as our happiness or misery, beyond which we have no concernment to know or to be. So that, I think, we may add to the two former sorts of knowledge this also, of the existence of particular external objects, by that perception and consciousness we have of the actual entrance of ideas from them, and allow these three degrees of knowledge, viz. intuitive , demonstrative , and sensitive ; in each of which there are different degrees and ways of evidence and certainty.

(From IV.iv.1— Objection: “Knowledge placed in our ideas may be all unreal or chimerical” ) I doubt not but my reader, by this time, may be apt to think that I have been all this while only building a castle in the air; and be ready to say to me: To what purpose all this stir? knowledge, say you, is only the perception of the agreement or disagreement of our own ideas: but who knows what those ideas may be? Is there anything so extravagant as the imaginations of men’s brains? where is the head that has no chimeras in it? … If it be true, that all knowledge lies only in the perception of the agreement or disagreement of our own ideas, the visions of an enthusiast and the reasonings of a sober man will be equally certain.

(From IV.iv.2— Answer Not so, where Ideas agree with Things ) To which I answer, That if our knowledge of our ideas terminate in them, and reach no further, where there is something further intended, our most serious thoughts will be of little more use than the reveries of a crazy brain. … But I hope, before I have done, to make it evident, that this way of certainty, by the knowledge of our own ideas, goes a little further than bare imagination: and I believe it will appear that all the certainty of general truths a man has lies in nothing else.

(From IV.iv.3— But what shall be the criterion of this agreement? ) It is evident the mind knows not things immediately, but only by the intervention of the ideas it has of them. Our knowledge, therefore, is real only so far as there is a conformity between our ideas and the reality of things. But what shall be here the criterion? How shall the mind, when it perceives nothing but its own ideas, know that they agree with things themselves? this, though it seems not to want difficulty, yet, I think, there be two sorts of ideas that we may be assured agree with things.

(From IV.iv.4— As, first all simple ideas are really conformed to things ) First , the first are simple ideas, which since the mind, as has been showed, can by no means make to itself, must necessarily be the product of things operating on the mind, in a natural way, and producing therein those perceptions which by the Wisdom and Will of our Maker they are ordained and adapted to. From whence it follows, that simple ideas are not fictions of our fancies, but the natural and regular productions of things without us, really operating upon us; and so carry with them all the conformity which is intended; or which our state requires: for they represent to us things under those appearances which they are fitted to produce in us: whereby we are enabled to distinguish the sorts of particular substances, to discern the states they are in, and so to take them for our necessities, and apply them to our uses. Thus the idea of whiteness, or bitterness, as it is in the mind, exactly answering that power which is in any body to produce it there, has all the real conformity it can or ought to have, with things without us. And this conformity between our simple ideas and the existence of things, is sufficient for real knowledge.

• What is the difference between knowledge and ‘real’ knowledge?
• How can we know whether we have ‘real’ knowledge or not?

Scholars disagree on just how Locke means to respond to skepticism. But it certainly looks as if he is invoking God at some crucial points in his defense of the reality of knowledge. What follows is Locke’s sketch of his argument for God’s existence; the details are to be found later in IV.x.

(From IV.x.1— We are capable of knowing certainly that there is a God ) Though God has given us no innate ideas of himself; though he has stamped no original characters on our minds, wherein we may read his being; yet having furnished us with those faculties our minds are endowed with, he hath not left himself without witness …

(From IV.x.2— For Man knows that he himself exists ) I think it is beyond question, that man has a clear idea of his own being; he knows certainly he exists, and that he is something. He that can doubt whether he be anything or no, I speak not to … This, then, I think I may take for a truth, which every one’s certain knowledge assures him of, beyond the liberty of doubting, viz. that he is something that actually exists .

(From IV.x.3— He knows also that Nothing cannot produce a Being; therefore something must have existed from Eternity ) In the next place, man knows, by an intuitive certainty, that bare nothing can no more produce any real being, than it can be equal to two right angles . [I]t is [thus] an evident demonstration, that from eternity there has been something ; since what was not from eternity had a beginning; and what had a beginning must be produced by something else.

(From IV.x.4— And that eternal being must be most powerful ) Next, it is evident, that what had its being and beginning from another, must also have all that which is in and belongs to its being from another too. All the powers it has must be owing to and received from the same source. This eternal source, then, of all being must also be the source and original of all power; and so this eternal being must be also the most powerful .

(From IV.x.5— And most knowing ) Again, a man finds in himself perception and knowledge. We have then got one step further; and we are certain now that there is not only some being, but some knowing, intelligent being in the world. There was a time, then, when there was no knowing being, and when knowledge began to be; or else there has been also a knowing being from eternity . If it be said, there was a time when no being had any knowledge, when that eternal being was void of all understanding; I reply, that then it was impossible there should ever have been any knowledge: it being as impossible that things wholly void of knowledge, and operating blindly, and without any perception, should produce a knowing being, as it is impossible that a triangle should make itself three angles bigger than two right ones. For it is as repugnant to the idea of senseless matter, that it should put into itself sense, perception, and knowledge, as it is repugnant to the idea of a triangle, that it should put into itself greater angles than two right ones.

(From IV.x.6— And therefore God ) Thus, from the consideration of ourselves, and what we infallibly find in our own constitutions, our reason leads us to the knowledge of this certain and evident truth— that there is an eternal, most powerful, and most knowing being ; which whether any one will please to call God, it matters not.

• Locke’s argument for God’s existence, as presented in these passages, looks pretty weak. What’s wrong with it?

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GREAT THINKERS John Locke

An Essay Concerning Human Understanding

Recommended edition:  An Essay Concerning Human Understanding , ed. Peter H. Nidditch (New York: Oxford University Press, 1975).

Since it is the understanding, that sets man above the rest of sensible beings, and gives him all the advantage and dominion, which he has over them; it is certainly a subject, even for its nobleness, worth our labour to inquire into. The understanding, like the eye, whilst it makes us see and perceive all other things, takes no notice of itself; and it requires art and pains to set it at a distance, and make it its own object. But, whatever be the difficulties that lie in the way of this inquiry; whatever it be, that keeps us so much in the dark to ourselves; sure I am, that all the light we can let in upon our own minds, all the acquaintance we can make with our own understandings, will not only be very pleasant, but bring us great advantage, in directing our thoughts in the search of other things.

This, therefore, being my purpose, to inquire into the original, certainty, and extent of human knowledge; together with the grounds and degrees of belief, opinion, and assent. … It shall suffice to my present purpose, to consider the discerning faculties of a man, as they are employed about the objects, which they have to do with: And I shall imagine I have not wholly misemployed myself in the thoughts I shall have on this occasion, if, in this historical, plain method, I can give any account of the ways, whereby our understandings come to attain those notions of things we have, and can set down any measures of the certainty of our knowledge, or the grounds of those persuasions, which are to be found amongst men, so various, different, and wholly contradictory; and yet asserted, somewhere or other, with such assurance and confidence, that he that shall take a view of the opinions of mankind, observe their opposition, and at the same time consider the fondness and devotion wherewith they are embraced, the resolution and eagerness wherewith they are maintained, may perhaps have reason to suspect, that either there is no such thing as truth at all; or that mankind hath no sufficient means to attain a certain knowledge of it.

It is, therefore, worth while to search out the bounds between opinion and knowledge; and examine by what measures, in things, whereof we have no certain knowledge, we ought to regulate our assent, and moderate our persuasions.

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The most important philosopher ever to write in English, David Hume (1711-1776) — the last of the great triumvirate of “British empiricists” — was also well-known in his own time as an historian and essayist. A master stylist in any genre, Hume's major philosophical works — A Treatise of Human Nature (1739-1740), the Enquiries concerning Human Understanding (1748) and concerning the Principles of Morals (1751), as well as the posthumously published Dialogues concerning Natural Religion (1779) — remain widely and deeply influential. Although many of Hume's contemporaries denounced his writings as works of scepticism and atheism, his influence is evident in the moral philosophy and economic writings of his close friend Adam Smith. Hume also awakened Immanuel Kant from his “dogmatic slumbers” and “caused the scales to fall” from Jeremy Bentham's eyes. Charles Darwin counted Hume as a central influence, as did “Darwin's bulldog,” Thomas Henry Huxley. The diverse directions in which these writers took what they gleaned from reading Hume reflect not only the richness of their sources but also the wide range of his empiricism. Today, philosophers recognize Hume as a precursor of contemporary cognitive science, as well as one of the most thoroughgoing exponents of philosophical naturalism.

1. Life and Works

2. some interpretive questions, 3. the treatise and the enquiries, 4. a third species of philosophy, 5. empiricism, 6. hume's account of definition, 7. association, 8. the universe of the imagination, 9. interpretive questions resolved, 10. causation and inductive inference: the negative phase, 11. causation and inductive inference: the positive phase, 12. necessary connection and the definition of cause, 13. moral philosophy, 14. politics, criticism, history, and religion, hume's works, bibliographical studies, works on hume, other internet resources, related entries.

Born in Edinburgh, Hume spent his childhood at Ninewells, the family's modest estate on the Whitadder River in the border lowlands near Berwick. His father died just after David's second birthday, “leaving me, with an elder brother and a sister under the care of our Mother, a woman of singular Merit, who, though young and handsome, devoted herself to the rearing and educating of her Children.” (All quotations in this section are from Hume's autobiographical essay, “My Own life”, reprinted in HL.)

Katherine Falconer Home realized that young David was “uncommonly wake-minded” — precocious, in her lowland dialect — so when his brother went up to Edinburgh University, David, not yet twelve, joined him. He read widely in history and literature, as well as ancient and modern philosophy, and also studied some mathematics and contemporary science.

Hume's family thought him suited for a career in the law, but he preferred reading classical authors, especially Cicero, whose Offices became his secular substitute for The Whole Duty of Man and his family's strict Calvinism. Pursuing the goal of becoming “a Scholar & Philosopher,” he followed a rigorous program of reading and reflection for three years until “there seem'd to be open'd up to me a New Scene of Thought.”

The intensity of developing this philosophical vision precipitated a psychological crisis in the isolated scholar. Believing that “a more active scene of life” might improve his condition, Hume made “a very feeble trial” in the world of commerce, as a clerk for a Bristol sugar importer. The crisis passed and he remained intent on articulating his “new scene of thought.” He moved to France, where he could live frugally, and finally settled in La Flèche, a sleepy village in Anjou best known for its Jesuit college. Here, where Descartes and Mersenne studied a century before, Hume read French and other continental authors, especially Malebranche, Dubos, and Bayle; he occasionally baited the Jesuits with iconoclastic arguments; and, between 1734 and 1737, he drafted A Treatise of Human Nature .

Hume returned to England in 1737 to ready the Treatise for the press. To curry favor with Bishop Butler, he “castrated” his manuscript, deleting his controversial discussion of miracles, along with other “nobler parts.” Book I, Of the Understanding , and Book II, Of the Passions , was published anonymously in 1739. Book III, Of Morals , appeared in 1740, as well as an anonymous Abstract of the first two books. Although other candidates, especially Adam Smith, have occasionally been proposed as the Abstract 's author, scholars now agree that it is Hume's work. The Abstract features a clear, succinct account of “one simple argument” concerning causation and the formation of belief. Hume's elegant summary presages his “recasting” of that argument in the first Enquiry .

The Treatise was no literary sensation, but it didn't “fall dead-born from the press,” as Hume disappointedly described its reception. And despite his surgical deletions, the Treatise attracted enough of a “murmour among the zealots” to fuel his life-long reputation as an atheist and a sceptic.

Back at Ninewells, Hume published two modestly successful volumes of Essays, Moral and Political in 1741 and 1742. When the Chair of Ethics and Pneumatical (“Mental”) Philosophy at Edinburgh became vacant in 1745, Hume hoped to fill it, but his reputation provoked vocal and ultimately successful opposition. Six years later, he stood for the Chair of Logic at Glasgow, only to be turned down again. Hume never held an academic post.

In the wake of the Edinburgh debacle, Hume made the unfortunate decision to accept a position as tutor to the Marquess of Annandale, only to find that the young man was insane and his estate manager dishonest. With considerable difficulty, Hume managed to extricate himself from this situation, accepting the invitation of his cousin, Lieutenant-General James St. Clair, to be his Secretary on a military expedition against the French in Quebec. Contrary winds delayed St. Clair's fleet until the Ministry canceled the plan, only to spawn a new expedition that ended as an abortive raid on the coastal town of L'Orient in Brittany.

Hume also accompanied St. Clair on an extended diplomatic mission to the courts of Vienna and Turin in 1748. (“I wore the uniform of an officer.”) While he was in Italy, the Philosophical Essays concerning Human Understanding appeared. A recasting of the central ideas of Book I of the Treatise , the Philosophical Essays were read and reprinted, eventually becoming part of Hume's Essays and Treatises under the title by which they are known today, An Enquiry concerning Human Understanding . In 1751, this Enquiry was joined by a second, An Enquiry concerning the Principles of Morals . Hume described the second Enquiry , a substantially rewritten version of Book III of the Treatise , as “incomparably the best” of all his works. More essays, the Political Discourses , appeared in 1752, and Hume's correspondence reveals that a draft of the Dialogues concerning Natural Religion was also well underway at this time.

An offer to serve as Librarian to the Edinburgh Faculty of Advocates gave Hume the opportunity to work steadily on another project, a History of England , which was published in six volumes in 1754, 1756, 1759, and 1762. His History became a best-seller, finally giving him the financial independence he had long sought. (Both the British Library and the Cambridge University Library still list him as “David Hume, the historian.”)

But even as a librarian, Hume managed to arouse the ire of the “zealots.” In 1754, his order for several “indecent Books unworthy of a place in a learned Library” prompted a move for his dismissal, and in 1756, an unsuccessful attempt to excommunicate him. The Library's Trustees canceled his order for the offending volumes, which Hume regarded as a personal insult. Since he needed the Library's resources for his History , Hume remained at his post, but he did turn over his salary to Thomas Blacklock, a blind poet he befriended and sponsored. Hume finished his research for the History in 1757, and quickly resigned to make the position available for Adam Ferguson.

Despite his resignation from the Advocates' Library and the success of his History , Hume's work continued to be surrounded by controversy. In 1755, he was ready to publish a volume that included The Natural History of Religion and A Dissertation on the Passions as well as the essays “Of Suicide” and “Of the Immortality of the Soul.” When his publisher, Andrew Millar, was threatened with legal action through the machinations of the minor theologian, William Warburton, Hume suppressed the offensive essays, substituting “Of Tragedy” and “Of the Standard of Taste” to round out his Four Dissertations , which was finally published in 1757.

In 1763, Hume accepted an invitation from Lord Hertford, the Ambassador to France, to serve as his Private Secretary. During his three years in Paris, Hume became Secretary to the Embassy and eventually its Chargè d'Affaires. He also become the rage of the Parisian salons, enjoying the conversation and company of Diderot, D'Alembert, and d'Holbach, as well as the attentions and affections of the salonnières , especially the Comtesse de Boufflers. (“As I took a particular pleasure in the company of modest women, I had no reason to be displeased with the reception I met with from them.”)

Hume returned to England in 1766, accompanied by Jean-Jacques Rousseau, who was then fleeing persecution in Switzerland. Their friendship ended quickly and miserably when the paranoid Rousseau became convinced that Hume was masterminding an international conspiracy against him.

After a year (1767-68) in London as an Under-Secretary of State, Hume returned to Edinburgh to stay in August, 1769. He built a house in Edinburgh's New Town, and spent his autumnal years quietly and comfortably, dining and conversing with friends, not all of whom were “studious and literary,” for Hume also found that his “company was not unacceptable to the young and careless.” One young person who found his company particularly “acceptable” was an attractive, vivacious, and highly intelligent woman in her twenties — Nancy Orde, the daughter of Chief Baron Orde of the Scottish Exchequer. One of Hume's friends described her as “one of the most agreeable and accomplished women I ever knew.” Also noted for her impish sense of humor, she chalked “St. David's Street” on the side of Hume's house one night; the street still bears that name today. The two were close enough that she advised Hume in choosing wallpaper for his new home, and rumors that they were engaged even reached the ears of the salonnières in Paris. Just before his death, Hume added a codicil to his will, which included a gift to her of “ten Guineas to buy a Ring, as a Memorial of my Friendship and Attachment to so amiable and accomplished a Person.”

Hume also spent considerable time in his final years revising his works for new editions of his Essays and Treatises , which contained his collected essays, the two Enquiries , A Dissertation on the Passions , and The Natural History of Religion , but — significantly — not A Treatise of Human Nature . In 1775, he added an “Advertisement” to these volumes, in which he appeared to disavow the Treatise . Though he regarded this note as “a compleat Answer” to his critics, especially “Dr. Reid and that biggotted, silly fellow, Beattie,” subsequent readers have wisely chosen to ignore Hume's admonition to ignore his greatest philosophical work.

Upon finding that he had intestinal cancer, Hume prepared for his death with the same peaceful cheer that characterized his life. He arranged for the posthumous publication of his most controversial work, the Dialogues concerning Natural Religion ; it was seen through the press by his nephew and namesake in 1779, three years after his uncle's death.

At the beginning of the first Enquiry , Hume maintains that we “must cultivate true metaphysics with some care, in order to destroy the false and adulterate” (EHU 12). But when he explains what “true metaphysics” is, it turns out not to be metaphysics at all. Hume is urging nothing less than the total reform of philosophy. A central part of his program is the profoundly anti-metaphysical aim of abandoning the a priori search for theoretical explanations that supposedly give us insight into the ultimate nature of reality, replacing these “hypothes[es], which can never be made intelligible” with an empirical, descriptive inquiry that answers questions about “the science of human nature” in the only way they can be intelligibly answered.

Understanding how and why Hume repudiates metaphysics will help us better understand the shape of his philosophical project. The best way to do that is to look at the places where Hume sets out his program for the reform of philosophy: the “Introduction” and the opening sections of A Treatise of Human Nature , and Section I of the first Enquiry . Looking afresh at these passages will not only clarify the nature of Hume's project, it will also help resolve several currently debated questions about it, including:

• the relation between the Treatise and the first Enquiry , and whether one work should be regarded as having interpretive priority over the other;
• the relation between the negative and positive aspects of his project;
• the nature of, and the proper relations among, his empiricism, his scepticism, and his naturalism.

These questions, especially the last, have generated increasingly complex responses in recent Hume scholarship.

Hume's apparent disavowal of the Treatise in his “Advertisement” raises a question as to how we should read his works. Should we take his “Advertisement” literally and let the Enquiries represent his considered view? Or should we take him seriously and conclude — whatever he may have said or thought — that the Treatise is the best statement of his position?

Both responses presuppose that there are substantial enough differences between the two works to warrant our reading them disjointly. This is highly dubious. Even in the “Advertisement,” Hume says that “most of the principles, and reasonings, contained in this volume, were published” in the Treatise , and that he has “cast the whole anew in the following pieces, where some negligences in his former reasoning and more in the expression, are…corrected” (EHU, “Advertisement”). Despite his protests, this hardly sounds like the claims of one who has genuinely repudiated his earlier work.

Hume reinforced this perspective when he wrote his friend Gilbert Elliot of Minto that “the philosophical principles are the same in both…by shortening and simplifying the questions, I really render them much more complete” (HL, I:158). And in “My Own Life,” he added that the Treatise's lack of success “proceeded more from the manner than the matter.” It is not unreasonable to conclude that Hume's “recasting” of the Treatise was primarily designed to address this point. The following brief overview of Hume's central views on method, epistemology, and ethics therefore follows the structure — “the manner” — of the Enquiries and emphasizes the content — “the matter” — they have in common with the Treatise .

In his “Introduction” to the Treatise , Hume bemoans the sorry state of philosophy, evident even to “the rabble without doors,” which has given rise to “that common prejudice against metaphysical reasonings of all kinds,” that is, “every kind of argument which is in any way abstruse, and requires some attention to be comprehended” (T, xiv).

Hume intends to correct this miserable situation. In An Enquiry concerning the Principles of Morals , he says that he will “follow a very simple method” that will nonetheless bring about “a reformation in moral disquisitions” similar to that recently achieved in natural philosophy, where we have been cured of “a common source of illusion and mistake” — our “passion for hypotheses and systems.” To make parallel progress in the moral sciences, we should “reject every system…however subtle or ingenious, which is not founded on fact and observation,” and “hearken to no arguments but those which are derived from experience” (EPM, 173-175).

The “hypotheses and systems” Hume has in mind cover a wide range of philosophical and theological views. These theories were too entrenched, too influential, and too different from his proposed science of human nature for him just to present his “new scene of thought” as their replacement. He needed to show why we should reject these theories, in order to make space to develop his own.

Hume outlines his strategy in the first section of An Enquiry concerning Human Understanding . Beginning by defining “moral philosophy” as “the science of human nature,” and thereby identifying his project with that of the Treatise , Hume distinguishes two “species,” or “two different manners” in which moral philosophy may be treated. Although seemingly encouraging us to regard them as mutually exclusive and jointly exhaustive, it is clear by the end of the section that Hume has rejected both species in favor of what he considers the proper way to pursue the science of human nature — a third species of philosophy.

The first species of philosophy looks at humans as active creatures, driven by desires and feelings and “influenced…by taste and sentiment,” seeking some things and avoiding others according to their perceived value. Since they regard virtue as the most valuable thing humans can pursue, these philosophers attempt “to excite and regulate our sentiments” in order to “bend our hearts to the love of probity and true honor.” They paint a flattering picture of human nature, easy to understand and even easier to accept. They make us feel what they say about our feelings, and what they say is so useful and agreeable that ordinary people are readily inclined to accept their views. This species of philosophy is easily recognizable as a generic characterization of positions defended in Hume's time by Shaftesbury and Francis Hutcheson.

In sharp contrast, the second species of philosophy seeks more to form our understandings than to cultivate our manners. These philosophers regard humans as reasonable rather than active creatures, and study human nature “to find those principles, which regulate our understanding, excite our sentiments, and make us approve or blame any particular object, action, or behaviour.” They seek to discover hidden truths that will “fix, beyond controversy, the foundations of morals, reasoning, and criticism.” In framing their theories, they move from particular cases to general principles, and continue to “push on their enquiries to principles more general,” until they arrive at “those original principles, by which, in every science, all human curiousity must be bounded” (EHU, 6). This view not only glorifies reason, but also appeals to it in its emphasis on rarefied speculation and abstract argument.

Hume is clear that “the generality of mankind” will always prefer the “easy and obvious philosophy” — his first species — over the “accurate and abstruse” second species. If they did so without “throwing any blame or contempt on the latter,” then perhaps no harm would be done. But repeating almost verbatim his point from the “Introduction” to the Treatise , Hume notes that “the matter is often carried farther, even to the absolute rejecting of all profound reasonings, or what is commonly called metaphysics” (EHU, 9).

Hostility to metaphysics, however, isn't entirely unjustified. It isn't merely obscure; it is also “the inevitable source of uncertainty and error.” This is “the justest and most plausible objection against a considerable part of metaphysics, that they are not properly a science.” Instead, these theories “arise either from the fruitless efforts of human vanity, which would penetrate into subjects utterly inaccessible to the understanding, or from the craft of popular superstitions, which, being unable to defend themselves on fair ground, raise these entangling branches to cover and protect their weakness” (EHU, 11).

Metaphysics not only indulges in speculation that goes well beyond the bounds of sense, and so loses its claim to be a science, it also aids and abets the construction of metaphysical smoke screens as cover for “popular superstitions.” Since this garbage won't degrade by itself, philosophers should “perceive the necessity of carrying the war into the most secret recesses of the enemy.” And the only way to convincingly reject the “abstruse questions” of traditional metaphysics is to “enquire seriously into the human understanding, and show, from an exact analysis of its powers and capacity, that it is by no means fitted for such remote and abstruse subjects…[We] must cultivate true metaphysics with some care, to destroy the false and adulterate” (EHU, 12).

Thus a prominent part of Hume's approach to discovering “the proper province of human reason” is essentially negative and critical. The only way of ridding ourselves of speculative metaphysicians and their religious camp followers is to engage with them, which demands that we also engage in difficult and sometimes very abstract arguments:

Accurate and just reasoning is the only catholic remedy, fitted for all persons and all dispositions, and is alone able to subvert that abstruse philosophy and metaphysical jargon, which being mixed up with popular superstition, renders it in a manner impenetrable to careless reasoners, and gives it the air of science and wisdom (EHU, 12-3).

But “besides this advantage of rejecting…[this] uncertain and disagreeable part of learning,” engaging in “accurate and just reasoning” is not just a negative activity: “there are many positive advantages, which result from accurate scrutiny into the powers and faculties of human nature” (EHU, 13).

Hume proposes to replace the “airy sciences” of the metaphysicians with a descriptive “delineation of the parts and powers of the mind.” He believes that traditional metaphysicians went wrong in speculating about the “ultimate original principles” governing human nature, which committed them to claims that go beyond what we can determine from experience in order to draw conclusions about the ultimate nature of reality. In doing so, they went beyond anything that could have legitimate cognitive content, which is why their “hypotheses and systems” aren't properly sciences — or even intelligible.

Hume makes the same point in the “Introduction” to the Treatise : “any hypothesis, that pretends to discover the ultimate original qualities of human nature, ought to be rejected as presumptuous and chimerical.” Once we see the “impossibility of explaining ultimate principles,” we can reject theories that pretend to provide them. And once we do, we can get clear about the proper way to study human nature: “The essence of the mind being equally unknown to us with that of external bodies, it must be equally impossible to form any notion of its powers and qualities otherwise than from careful and exact experiments, and the observation of particular effects, which result from different circumstances and situations.” So the Treatise also recommends the repudiation of metaphysics, and outlines a positive program whereby “the only solid foundation” for the science of human nature “must be laid on experience and observation” (T, xvi-xvii).

When Hume spells out this same positive program in the Enquiry , he first calls his project “true metaphysics,” to mark the contrast with the “false metaphysics” he has rejected. But when he explains what “true metaphysics” is, it isn't metaphysics at all. It is an empirical inquiry, not an a priori one, and as such, is a genuine alternative to the contentless speculations of previous philosophies. His preferred terms for his project, “mental geography” and “anatomy of the mind,” are better characterizations of how he conceives of his descriptive anti-metaphysical alternative to traditional ways of theorizing about human nature.

Hume's program for reform in philosophy thus has two related aspects: the elimination of metaphysics and the establishment of an empirical experimental science of human nature. He shifts the focus away from the traditional metaphysical search for “ultimate original principles” in order to concentrate on describing the “original principles” of human nature that we can discover through experience and observation, and to which we can give coherent cognitive content by tracing the ideas involved to the impressions that gave rise to them. He does so because claims to have found “ultimate principles” are not just false, they are incoherent, because they go beyond anything that can be experienced.

This combination of negative and positive aims is a distinguishing feature of Hume's particular brand of empiricism, and the strategy he devised to achieve these aims is revelatory of his philosophical genius. For Hume, all the materials of thinking — perceptions — are derived either from sensation (“outward sentiment”) or from reflection (“inward sentiment”) (EHU, 19). He divides perceptions into two categories, distinguished by their different degrees of force and vivacity. Our “more feeble” perceptions, ideas , are ultimately derived from our livelier impressions (EHU, Section II; T, I.i.1-2).

Hume begins both the Treatise and the Enquiry with an account of impressions and ideas because he thinks that all contentful philosophical questions can be asked and answered in those terms. Trying to go beyond perceptions, as metaphysics must, inevitably involves going beyond anything that can have cognitive content. No wonder the “hypotheses” that purport to give us the “ultimate original principles” that constitute traditional metaphysics turn out to be incoherent.

Although we permute and combine ideas in the imagination to form complex ideas of things we haven't experienced, Hume is adamant that our creative powers extend no farther than “the materials afforded us by the senses and experience.” Complex ideas are composed of simple ideas , which are fainter copies of the simple impressions from which they are ultimately derived, to which they correspond and exactly resemble. Hume offers this “general proposition” as his “first principle…in the science of human nature” (T, 7). Usually called the “Copy Principle,” Hume's distinctive brand of empiricism is often identified with his commitment to it.

Hume presents the Copy Principle as an empirical thesis. He emphasizes this point by offering “one contradictory phenomenon” (T, 5-6; EHU, 20-21) — the infamous missing shade of blue — as an empirical counterexample to the Copy Principle. Hume asks us to consider “a person to have enjoyed his sight for thirty years, and to have become perfectly well acquainted with colours of all kinds, excepting one particular shade of blue…”(T, 6). Then

“Let all the different shades of that colour, except that single one, be plac'd before him, descending gradually from the deepest to the lightest; ‘tis plain, that he will perceive a blank, where that shade is wanting, and will be sensible, that there is a greater distance in that place betwixt the contiguous colours, than in any other. Now I ask, whether ‘tis possible for him, from his own imagination, to supply this deficiency, and raise up to himself the idea of that particular shade, tho’ it had never been conveyed to him by his senses? I believe there are few but will be of the opinion that he can; and this may serve as a proof, that the simple ideas are not always derived from the correspondent impressions; tho’ the instance is so particular and singular, that ‘tis scarce worth our observing, and does not merit that for it alone we should alter our general maxim” (T 6).

Hume's critics have objected that in offering this counterexample, he either unwittingly destroys the generality of the Copy Principle, which he needs, given the uses to which he will put it, or else his dismissive attitude toward the counterexample reflects his disingenuous willingness to apply the Copy Principle arbitrarily, while pretending that it really possesses the generality his uses of it require.

Hume's defenders, on the other hand, maintain either that he should have granted that the imaginative construction of the missing shade really produces a complex idea, or that he should have insisted that such counterexamples are exceedingly rare, and that the contentious metaphysical ideas, the cognitive content of which he uses the Copy Principle to critique, are not possibly ideas that could be generated by the imagination in the way the idea of the missing shade is supposedly generated.

Maintaining that the imaginatively constructed shade is a complex idea runs counter to what Hume actually says, however, and without some reason to convince us that philosophically contentious ideas couldn't also be constructed in similar ways by the imagination, the claim remains unsupported and therefore unsatisfying.

Fortunately, there is a more satisfying resolution of the issue raised by the missing shade available to Hume. Once arranged in the way Hume describes, the simple ideas of the shades of blue that we have experienced bear a close mental resemblance to a paint store's familiar physical chips of the various shades, displayed on cardboard ordered by shade. Hume plausibly maintains that we would first notice that there is a gap where the shade is missing from our mental ordering of the shades of blue, just as we would also easily notice when a chip was missing from the physical array.

Even though each physical chip presents us with what for Hume is a simple impression of that shade, the paint store also has a formula for mixing paint of that shade. The formula gives the proportions of the component color pigments that are needed to create paint of that exact shade. Once mixed, however, when we perceive the newly mixed paint, we are now having a simple impression (ignoring the fact that the paint is spatially extended and therefore gives us a complex impression of many simple impressions of the shade) of the previously missing shade. We can't decompose the paint, once mixed, in the way that (say) we can take apart a car. In Humean terms, our idea of the shade of blue is simple, while our idea of the car is complex.

Now consider creating the missing physical shade by simply mixing the appropriate proportions of the shades on either side of the space where it should be. When we perceive the result of the mixing, we again have a simple impression of the no-longer missing physical shade of blue. So now imagine doing an analogous kind of “mental mixing” in the imagination: although the missing shade is now mentally mixed from two simple ideas, the result is a single shade of blue, and so should also be a simple idea, just like the ideas of each individual shade on either side of it in the array.

Although the missing shade has no direct antecedent in impressions, it is not totally independent of them, either. The two shades that were used to mentally mix the the formerly missing shade were caused by and resemble simple impressions in the usual way. We can also immediately see that there is an extremely limited number of ideas that could be caused in this or any other closely related manner, so the fear that admitting the creation of the missing shade would open the floodgates to a range of philosophically suspect ideas is not a realistic one. Besides, most of these theoretical notions would be complex, anyway. So Hume can retain the Copy Principle as an empirical principle, admit this harmless counterexample to it as genuine, and still use the Copy Principle as a way of determining cognitive content, or lack of it.

While Hume's empiricism is usually identified with the Copy Principle, it is his use of its reverse in his account of definition that is really the most distinctive and innovative element of his system.

As his diagnosis of traditional metaphysics indicates, Hume believes that “the chief obstacle…to our improvement in the moral or metaphysical sciences is the obscurity of the ideas, and ambiguity of the terms” (EHU, 61). However, Hume argues that conventional definitions — defining terms in terms of other terms — replicate philosophical confusions by substituting synonyms for the original and thus never break out of a narrow “definitional circle.” Determining the cognitive content of an idea or term requires something else.

To make progress, we need “to pass from words to the true and real subject of the controversy” (EHU 80) — the ideas involved. Hume believes he has found a mechanism that permits us to do so — his account of definition, which he touts as “a new microscope or species of optics” (EHU 62), predicting that it will produce as dramatic results in the moral sciences as its hardware counterparts have produced in natural philosophy.

This account of definition is a device for precisely determining the cognitive content of words and ideas. Hume uses a simple series of tests to determine cognitive content. Begin with a term. Ask what idea is annexed to it. If there is no such idea, then the term has no cognitive content, however prominently it figures in philosophy or theology. If there is an idea annexed to the term, and it is complex, break it up into the simple ideas that compose it. Then trace the simple ideas back to their original impressions: “These impressions are all strong and sensible. They admit not of ambiguity. They are not only placed in a full light themselves, but may throw light on their correspondent ideas, which lie in obscurity” (EHU, 62).

If the process fails at any point, the idea in question lacks cognitive content. When carried through successfully, however, the theory yields a “just definition” — a precise account of the troublesome idea or term. So, whenever we are suspicious that a “philosophical term is employed without any meaning or idea (as is too frequent), we need but enquire, from what impression is that supposed idea derived ? And if it be impossible to assign any, this will serve to confirm our suspicion. By bringing ideas into so clear a light we may reasonably hope to remove all dispute, which may arise, concerning their nature and reality” (EHU, 22; Abstract , T, 648-9).

The Copy Principle accounts for the origins of our ideas. But our ideas are also regularly connected . As Hume put the point in his “Abstract” of the Treatise , “there is a secret tie or union among particular ideas, which causes the mind to conjoin them more frequently together, and makes the one, upon its appearance, introduce the other” (T, 662).

A science of human nature should account for these connections. Otherwise, we are stuck with an eidetic atomism — a set of discrete, independent ideas, unified only in that they are the contents of a particular mind. Eidetic atomism thus fails to explain how ideas are “bound together,” and its inadequacy in this regard encourages us, as Hume thought it encouraged Locke, to postulate theoretical notions — power and substance being the most notorious — to account for the connections we find among our ideas. Eidetic atomism is thus a prime source of the philosophical “hypotheses” Hume aims to eliminate.

Hume argues that, although “it be too obvious to escape observation, that different ideas are connected together; I do not find that any philosopher has attempted to enumerate or class all the principles of accociation” (EHU 24). His introduction of these “principles of association” is the other distinctive feature of his empiricism, so distinctive that in the Abstract he advertises it as his most original contribution: “If any thing can intitle the author to so glorious a name as that of an inventor, ‘tis the use he makes of the principle of the association of ideas” (T, 661-662).

The principles required for connecting our ideas aren't theoretical and rational; they are natural operations of the mind that we experience in “internal sensation.” Hume identifies “three principles of connexion” or association: resemblance, contiguity, and cause and effect. Of the three, causation is the strongest:

there is no relation, which produces a stronger connexion in the fancy, and makes one idea more readily recall another, than the relation of cause and effect betwixt their objects. (T, 11)

Causation is also the only associative principle that takes us “beyond the evidence of our memory and senses.” It establishes a link or connection between past and present experiences with events that we predict or explain, so that “all reasonings concerning matter of fact seem to be founded on the relation of cause and effect.” Causation is also the least understood of the associative principles, but “we shall have occasion afterwards to examine it to the bottom, and therefore shall not at present insist upon it” (T, 11).

Hume suggests that his identification of the principles of association is the equivalent, for the science of human nature, of Newton's discovery of the Law of Gravitation for the physical world, and like the inverse square law, the associative principles are “original.” Trying to account further for them takes one illegitimately beyond the bounds of experience:

Here is a kind of Attraction, which in the mental world will be found to have as extraordinary effects as in the natural, and to shew itself in as many and as various forms. Its effects are every where conspicuous; but as to its causes, they are mostly unknown, and must be resolv'd into original qualities of human nature, which I pretend not to explain. Nothing is more requisite for a true philosopher, than to restrain the intemperate desire of searching into causes, and having establish'd any doctrine upon a sufficient number of experiments, rest contented with that, when he sees a farther examination would lead him into obscure and uncertain speculations. (T, 13)

Hume believes that the science of human nature can only be intelligibly and successfully pursued in terms of the “original principles” he has identified, impressions and the associative mechanisms:

Since nothing is ever present to the mind but perceptions, and since all ideas are deriv'd from something antecedently present to the mind, it follows, that 'tis impossible for us so much as to conceive or form an idea of any thing specifically different from ideas and impressions. Let us fix our attention out of ourselves as much as possible; let us chase our imagination to the heavens, or to the utmost limits of the universe; we never really advance a step beyond ourselves, nor can conceive any kind of existence, but those perceptions, which have appear'd in that narrow compass. This is the universe of the imagination, nor have we any idea but what is there produc'd. (T, 67-8)

Hume explains more about how “the universe of the imagination” works in Part iii, Book I, of the Treatise :

Belief or assent , which always attends the memory and senses, is nothing but the vivacity of those perceptions they present; and that this alone distinguishes them from the imagination. To believe is in this case to feel an immediate impression of the senses, or a repetition of that impression in the memory. 'Tis merely the force and liveliness of the perception, which constitutes the first act of the judgment, and lays the foundation of that reasoning, when we trace the relation of cause and effect. (T, 86)

“We form a kind of system” of these strong impressions of sense and memory,“ comprehending whatever we remember to have been present, either to our internal perception or senses; and every particular of this system, joined to the present impressions, we are pleas'd to call a reality ” (T, 108). So although impressions are not, strictly speaking, capable of truth or falsity, the systematic character of the “universe of the imagination” gives us a means of accepting or rejecting impressions. The standard, roughly, is coherence :

As to those impressions, which arise from the senses , their ultimate cause is, in my opinion, perfectly inexplicable by human reason, and 'twill always be impossible to decide with certainty, whether they arise immediately from the object, or are produc'd by the creative power of the mind, or are deriv'd from the author of our being. Nor is such a question in any way material to our present purpose. We may draw inferences from the coherence of our perceptions, whether they be true or false; whether they represent nature justly, or be mere illusions of the senses. (T, 84)

Impressions, like passions, pleasures and pains, are “original existences,” which “arise in the soul originally from unknown causes” (T, 7). Only ideas can represent something beyond themselves; they represent the impressions that caused them, which they copy. Thus they are capable of truth or falsity, of accurate representation or misrepresentation. Impressions, however, are not representative and so they are not, strictly speaking, capable of truth or falsity.

Impressions are corrigible, however, and they can be measured by a standard. There is a distinction between the corrigibility of a perception and its being a representation of something external to itself. So denying that impressions are representative of something over and above other perceptions does not commit Hume to some version of subjectivism or idealism.

Hume's “system,” however, isn't complete when “the universe of the imagination” is populated only with impressions of sense and memories. As he stated earlier, the senses and memory are only “the first acts of judgment.” For

the mind stops not here. For finding, with this system of perceptions there is another connected by custom, or, if you will, by the relation of cause and effect, it proceeds to the consideration of their ideas; and as it feels that 'tis in a manner necessarily determin'd to view these particular ideas, and that the custom or relation, by which it is determin'd, admits not of the least change, it forms them into a new system, which it likewise dignifies with the title of realities . The first of these systems is the object of the memory and senses; the second of the judgment. (T, 108)

With the addition of causation, Hume's “system” now extends beyond the immediate testimonies of our senses and the records of our memories, providing a much more extensive web of belief, and a more fine-grained mechanism for accepting or rejecting impressions on the basis of their coherence, or lack of it, with the whole. Causal inference, Hume maintains

peoples the world, and brings us acquainted with such existences as, by their removal in time and place, lie beyond the reach of my senses and memory. By means of it I paint the universe in my imagination, and fix my attention on any part of it I please. (T, 108)

Hume's “system” now incorporates all his beliefs:

All this, and every thing else which I believe, are nothing but ideas, tho', by their force and settlled order, arising from custom and the relation of cause and effect, they distinguish themselves from the other ideas, which are merely the offspring of the imagination. (T, 108)

In saying that everything he believes is “nothing but ideas,” Hume is saying that everything he believes can be traced back to perceptions. But the buck stops there. Speculating about the causes of perceptions, where those causes are supposed to be something over and above perceptions, is to engage in the kind of search for “ultimate principles” that he has rejected, along with traditional metaphysics, as incoherent. That is what he means by saying that perceptions are “original existences.”

This should not be read as claiming that Hume thinks of the observations a Humean scientist of human nature is supposed to carry out as a matter of “observing his Lockean ideas by introspection.” Rather, as Janet Broughton stresses,

we ought to think of the scientist of man as being perfectly entitled to observe people seeing, hearing (etc.) things, and perfectly entitled to discriminate between perceptions that are sensations (seeing, hearing, etc., something) and those that are not. (“What Does the Scientist of Man Observe?” Hume Studies 18.2 (1992): 155-68)

The testimony of others can lead me to revise my “system,” but receiving their testimony is a latter of my having certain experiences. These experiences consist of various complex perceptions, but constitute my experience of books, papers, table, chairs, and other people.

Here is a sketch of how Hume's “system” works:

When I wake up and hear certain familiar sounds, I come to believe that it is raining. My judgment is a representation because there are perceptions of the sight and feel of rain, perceptions that I will have if I go to the window and look, or if I go outside and feel the rain. These perceptions are the “facts” my judgment is about. My judgment is the result of a causal process: given my past associations between a certain kind of sound and the presence of rain, plus a present impression of that certain kind of sound, I expect that if I go to the window I will see it raining on my roses. My expectation is representative, and capable of truth or falsity. So if I go to the window to look at my roses, and see that Charlotte is hosing off the screen on our bedroom window, then my belief misrepresented the facts, and what I believed was false. But the facts that lead me to regard my judgment as true or false, as accurately representing or as misrepresenting those facts, are themelves perceptions — impressions, and they are not representative of anything beyond themselves.

Just as individual impressions are corrigible, the system as a whole is fallible, and thus fallibility is at the heart of what Hume in the first Enquiry calls “mitigated scepticism.” Modifying and — it is to be hoped — improving the system is a process best described by Neurath's metaphor of the sailors who must repair their boat while keeping it afloat. Hume has shown that a system allegedly built on more secure “foundations” — “principles” that go beyond perceptions and are somehow supposed to validate them — is a metaphysical pipe-dream, not the legitimate basis of a coherent account of human nature, judgment, and belief.

But in rejecting the “ultimate principles” of traditonal metaphysics as incoherent, isn't Hume committing himself to an equally questionable picture of the ultimate nature of reality, one that says that there are only impressions, ideas, and the inferences we make from them? No. In choosing to restrict his discussion of questions about the nature of human nature in terms of perceptions, Hume is answering what he takes to be empirical questions in the only coherent way that they can be answered. Metaphysics tempts us to regard these answers as making claims about the ultimate nature of reality. Hume shows us how to resist that temptation. It is in this that the depth and originality of his project for the reform of philosophy consists.

The account we now have before us of the methodology and the basic elements of Hume's philosophy will go a long way toward resolving the questions of interpretation raised earlier. In particular, this account has shown that:

• Whatever the differences between the Treatise and the first Enquiry , the project Hume proposes is substantially the same in both works;
• Hume's project clearly involves both a negative or critical phase, the elimination of metaphysics, as well as a positive or constructive phase of developing an empirical, descriptive science of human nature. The two aspects of his project are brought to together by the device he employs to carry out each phase — his account of definition as a way of accurately determining cognitive content, or the lack of it;
• Hume's empiricism is defined by his treatment of the science of human nature as an empirical inquiry, rooted in experience and observation, and his naturalism is also closely related to his conception of his project as an empirical inquiry, to his limitation of investigation to “original principles,” and his repudiation of any attempt to discover “ultimate original qualities” in the study of human nature. Hume's scepticism has two aspects: the first is scepticism about the possibility of metaphysical theories, or any “hypothesis or system” that attempts to go beyond experience and observation. (This kind of scepticism about certain ways of doing philosophy shouldn't be confused with philosophical scepticism .) The second aspect of his scepticism is what Hume calls “mitigated or moderate scepticism,” which we might more naturally today call “fallibilism”: it consists of the recognition of our cognitive limitations and proneness to cognitive errors, as well as an injunction to limit inquiry “to such subjects as are best adapted to the narrow limits of human understanding” (EHU, 162), by which he means those to which we can give clear cognitive content, which dovetails nicely with the other aspects of his program.

Causation is not only the strongest associative relation, it is also the most important, since “by means of that relation alone we can go beyond the evidence of our memory and senses.” So causation is the basis of all our reasoning concerning matters of fact, and in our “reasonings … it is constantly supposed that there is a connexion between the present fact and that which is inferred from it” (EHU, 26-7).

The next question, then, is: What is the nature of this “connexion” and how is it established?

Hume proceeds first negatively, to show that our causal inferences are not due to reason, or any operation of the understanding. Reasoning concerns either relations of ideas or matters of fact . Hume quickly establishes that, whatever assures us that a causal relation obtains, it is not reasoning concerning relations between ideas. Effects are distinct events from their causes: we can always conceive of one such event occurring and the other not. So causal reasoning can't be a priori reasoning.

Causes and effects are discovered, not by reason but through experience, when we find that particular objects are constantly conjoined with one another. We tend to overlook this because most ordinary causal judgments are so familiar; we've made them so many times that our judgment seems immediate. But when we consider the matter, we realize that “an (absolutely) unexperienced reasoner could be no reasoner at all” (EHU, 45n). Even in applied mathematics, where we use abstract reasoning and geometrical methods to apply principles we regard as laws to particular cases in order to derive further principles as consequences of these laws, the discovery of the original law itself was due to experience and observation, not to a priori reasoning.

Even after we have experience of causal connections, our conclusions from those experiences aren't based on any reasoning or on any other process of the understanding. They are based on our past experiences of similar cases, without which we could draw no conclusions at all.

But this leaves us without any link between the past and the future. How can we justify extending our conclusions from past observation and experience to the future? The connection between a proposition that summarizes past experience and one that predicts what will occur at some future time is surely not an intuitive connection; it needs to be established by reasoning or argument. The reasoning involved must either be demonstrative , concerning relations of ideas, or probable , concerning matters of fact and existence.

There is no room for demonstrative reasoning here. We can always conceive of a change in the course of nature. However unlikely it may seem, such a supposition is intelligible and can be distinctly conceived. It therefore implies no contradiction, so it can't be proven false by a priori demonstrative reasoning.

Probable reasoning can't establish the connection, either, since it is based on the relation of cause and effect. What we understand of that relation is based on experience and any inference from experience is based on the supposition that nature is uniform — that the future will be like the past.

The connection could be established by adding a premise stating that nature is uniform. But how could we justify such a claim? Appeal to experience will either be circular or question-begging. For any such appeal must be founded on some version of the uniformity principle itself — the very principle we need to justify.

This argument exhausts the ways reason might establish a connection between cause and effect, and so completes the negative phase of Hume's project. The explanatory model of human nature which makes reason prominent and dominant in thought and action is indefensible. Scepticism about it is well-founded: the model must go.

Hume insists that he offers his “sceptical doubts about the operations of the understanding,” not as “discouragement, but rather an incitement…to attempt something more full and satisfactory” (EHU, 26). Having cleared a space for his own account, Hume is now ready to do just that.

Hume's negative argument showed that our causal expectations aren't formed on the basis of reason. But we do form them, and “if the mind be not engaged by argument…it must be induced by some other principle of equal weight and authority” (EHU, 41).

This principle can't be some “intricate or profound” metaphysical argument Hume overlooked. For all of us — ordinary people, infants, even animals — “improve by experience,” forming causal expectations and refining them in the light of experience. Hume's “sceptical solution” limits our inquiries to common life, where no sophisticated metaphysical arguments are available and none are required.

When we examine experience to see how expectations are actually produced, we discover that they arise after we have experienced “the constant conjunction of two objects;” only then do we “expect the one from the appearance of the other.” But when “repetition of any particular act or operation produces a propensity to renew the same act or operation…we always say, that this propensity is the effect of Custom ” (EHU, 43).

So the process that produces our causal expectations is itself causal. Custom or habit “determines the mind…to suppose the future conformable to the past.” But if this background of experienced constant conjunctions was all that was involved, then our “reasonings” would be merely hypothetical. Expecting that fire will warm, however, isn't just conceiving of its warming, it is believing that it will warm.

Belief requires that there also be some fact present to the senses or memory, which gives “strength and solidity to the related idea.” In these circumstances, belief is as unavoidable as is the feeling of a passion; it is “a species of natural instinct,” “the necessary result of placing the mind” in this situation.

Belief is “a peculiar sentiment, or lively conception produced by habit” that results from the manner in which ideas are conceived, and “in their feeling to the mind.” It is “nothing but a more vivid, lively, forcible, firm, steady conception of an object, than what the imagination alone is ever able to attain” (EHU, 49). Belief is thus “more an act of the sensitive, than of the cogitative part of our natures” (T, 183), so that “all probable reasoning is nothing but a species of sensation” (T, 103). This should not be surprising, given that belief is “so essential to the subsistence of all human creatures.” “It is more conformable to the ordinary wisdom of nature to secure so necessary an act of the mind, by some instinct or mechanical tendency” than to trust it “to the fallacious deductions of our reason” (EHU, 55). Hume's “sceptical solution” thus gives a descriptive alternative, appropriately “independent of all the laboured deductions of the understanding,” to philosophers' attempts to account for our causal “reasonings” by appeal to reason and argument. For the other notions in the definitional circle, “either we have no idea of force or energy, and these words are altogether insignificant, or they can mean nothing but that determination of the thought, acquir'd by habit, to pass from the cause to its usual effect” (T, 657).

Although causation is the strongest associative relation, as well as the most important, our philosophical understanding of causation and the ideas closely related to it is seriously deficient: “there are no ideas, which occur in metaphysics, more obscure and uncertain, than those of power, force, energy or necessary connexion” (EHU, 61-2). Hume wants to “fix, if possible, the precise meaning of these terms, and thereby remove some part of that obscurity, which is so much complained of in this species of philosophy” (EHU, 62). This project provides a crucial experiment for Hume's account of definition, one designed to prove the worth of his method, to provide a paradigm for investigating problematic philosophical and theological notions, and to supply valuable material for these inquiries. In doing so, he accounts in his own terms for the necessary connection so many philosophers have taken to be an essential component of the idea of causation.

As we should expect from the preceding discussion, when we examine a single case of two events we regard as causally related, our impressions are only of their conjunction ; the single case, taken by itself, yields no notion of their connection . When we go beyond the single case to examine the background of experienced constant conjunctions of similar pairs of events, we find little to add, for “there is nothing in a number of instances, different from every single instance, which is supposed to be exactly similar” (EHU, 75). How can the mere repetition of conjunctions produce a connection ?

While there is indeed nothing added to our external senses by this exercise, something does happen: “after a repetition of similar instances, the mind is carried by habit, upon the appearance of one event, to expect its usual attendant, and to believe that it will exist.” We feel this transition as an impression of reflection , or internal sensation , and it is this feeling of determination that is “the sentiment or impression from which we form the idea of power or necessary connexion. Nothing farther is in the case” (EHU, 75).

Although the impression of reflection — the internal sensation — is the source of our idea of the connection, that experience wouldn't have occurred if we hadn't had the requisite impressions of sensation — the external impressions — of the current situation, together with the background of memories of our past impressions of relevant similar instances.

All the impressions involved are relevant to a complete account of the origin of the idea, even though they seem, strictly speaking, to be “drawn from objects foreign to the cause.”

Hume sums up all of the relevant impressions in not one but two definitions of cause . The relation — or the lack of it — between these definitions has been a matter of considerable controversy. If we follow his account of definition, however, the first definition, which defines a cause as “ an object, followed by another, and where all objects similar to the first are followed by objects similar to the second ” (EHU, 76), accounts for all the external impressions involved in the case. His second definition, which defines a cause as “ an object followed by another, and whose appearance always conveys the thought to that other ” (EHU, 77) captures the internal sensation — the feeling of determination — involved. Both are definitions, by Hume's account, but the “just definition” of cause he claims to provide is expressed only by the conjunction of the two: only together do the definitions capture all the relevant impressions involved.

Hume's account of causation provides a paradigm of how philosophy, as he conceives it, should be done. He goes on to apply his method to other thorny traditional problems of philosophy and theology: liberty and necessity, miracles, design. In each case, the moral is that a priori reasoning and argument gets us nowhere: “it is only experience which teaches us the nature and bounds of cause and effect, and enables us to infer the existence of one object from that of another. Such is the foundation of moral reasoning, which forms the greater part of human knowledge, and is the source of all human action and behaviour” (EHU, 164). Since we all have limited experience, our conclusions should always be tentative, modest, reserved, cautious. This conservative, fallibilist position, which Hume calls mitigated scepticism , is the proper epistemic attitude for anyone “sensible of the strange infirmities of human understanding” (EHU, 161).

The cautious attitude Hume recommends is noticeably absent in moral philosophy, where “systems and hypotheses” have also “perverted our natural understanding,” the most prominent being the views of the moral rationalists — Samuel Clarke, Locke, and William Wollaston, the theories of “the selfish schools” — Hobbes and Mandeville — and the pernicious theological ethics of “the schools,” whose promotion of the dismal “monkish virtues” frame a catalogue of virtues diametrically opposed to Hume's. Although he offers arguments against the “systems” he opposes, Hume thinks the strongest case against them is to be made descriptively: all these theories offer accounts of human nature that experience and observation prove false.

Against the moral rationalists — the intellectualists of moral philosophy — who hold that moral judgments are based on reason, Hume maintains that it is difficult even to make their hypotheses intelligible (T, 455-470; EPM, Appendix I). Reason, Hume argues, judges either of matters of fact or of relations. Morality never consists in any single matter of fact that could be immediately perceived, intuited, or grasped by reason alone; morality for rationalists must therefore involve the perception of relations. But inanimate objects and animals can bear the same relations to one another that humans can, though we don't draw the same moral conclusions from determining that objects or animals are in a given relation as we do when humans are in that same relation. Distinguishing these cases requires more than reason alone can provide. Even if we could determine an appropriate subject-matter for the moral rationalist, it would still be the case that, after determining that a matter of fact or a relation obtains, the understanding has no more room to operate, so the praise or blame that follows can't be the work of reason.

Reason, Hume maintains, can at most inform us of the tendencies of actions. It can recommend means for attaining a given end, but it can't recommend ultimate ends. Reason can provide no motive to action, for reason alone is insufficient to produce moral blame or approbation. We need sentiment to give a preference to the useful tendencies of actions.

Finally, the moral rationalists' account of justice fares no better. Justice can't be determined by examining a single case, since the advantage to society of a rule of justice depends on how it works in general under the circumstances in which it is introduced.

Thus the views of the moral rationalists on the role of reason in ethics, even if they can be made coherent, are false.

Hume then turns to the claims of “the selfish schools,” that morality is either altogether illusory (Mandeville) or can be reduced to considerations of self-interest (Hobbes). He argues that an accurate description of the social virtues, benevolence and justice, will show that their views are false.

There has been much discussion over the differences between Hume's presentation of these arguments in the Treatise and the second Enquiry . “Sympathy” is the key term in the Treatise , while “benevolence” does the work in the Enquiry . But this need not reflect any substantial shift in doctrine. If we look closely, we see that benevolence plays much the same functional role in the Enquiry that sympathy plays in the Treatise . Hume sometimes describes benevolence as a manifestation of our “natural” or “social sympathy.” In both texts, Hume's central point is that we experience this “feeling for humanity” in ourselves and observe it in others, so “the selfish hypothesis” is “contrary both to common feeling and to our most unprejudiced notions” (EPM, 298).

Borrowing from Butler and Hutcheson, Hume argues that, however prominent considerations of self-interest may be, we do find cases where, when self-interest is not at stake, we respond with benevolence, not indifference. We approve of benevolence in others, even when their benevolence is not, and never will be, directed toward us. We even observe benevolence in animals. Haggling over how much benevolence is found in human nature is pointless; that there is any benevolence at all refutes the selfish hypothesis.

Against Hobbes, Hume argues that our benevolent sentiments can't be reduced to self-interest. It is true that, when we desire the happiness of others, and try to make them happy, we may enjoy doing so. But benevolence is necessary for our self-enjoyment, and although we may act from the combined motives of benevolence and enjoyment, our benevolent sentiments aren't identical with our self-enjoyment.

We approve of benevolence in large part because it is useful. Benevolent acts tend to promote social welfare, and those who are benevolent are motivated to cultivate the other social virtue, justice. But while benevolence is an original principle in human nature, justice is not. Our need for rules of justice isn't universal; it arises only under conditions of relative scarcity, where property must be regulated to preserve order in society.

The need for rules of justice is also a function of a society's size. In very small societies, where the members are more of an extended family, there may be no need for rules of justice , because there is no need for regulating property — no need, indeed, for our notion of property at all. Only when society becomes extensive enough that it is impossible for everyone in it to be part of one's “narrow circle” does the need for rules of justice arise.

The rules of justice in a given society are “the product of artifice and contrivance.” They are constructed by the society to solve the problem of how to regulate property; other rules might do just as well. The real need is for some set of “general inflexible rules…adopted as best to serve public utility” (EPM, 305).

Hobbesians try to reduce justice to self-interest, because everyone recognizes that it is in their interest that there be rules regulating property. But even here, the benefits for each individual result from the whole scheme or system being in place, not from the fact that each just act benefits each individual directly. As with benevolence, Hume argues that we approve of the system itself even where our self-interest isn't at stake. We can see this not only from cases in our own society, but also when we consider societies distant in space and time.

Hume's social virtues are related. Sentiments of benevolence draw us to society, allow us to perceive its advantages, provide a source of approval for just acts, and motivate us to do just acts ourselves. We approve of both virtues because we recognize their role in promoting the happiness and prosperity of society. Their functional roles are, nonetheless, distinct. Hume compares the benefits of benevolence to “a wall, built by many hands, which still rises by every stone that is heaped upon it, and receives increase proportional to the diligence and care of each workman,” while the happiness justice produces is like the results of building “a vault, where each individual stone would, of itself, fall to the ground” (EPM, 305).

“Daily observation” confirms that we recognize and approve of the utility of acts of benevolence and justice. While much of the agreeableness of the utility we find in these acts may be due to the fact that they promote our self-interest, it is also true that, in approving of useful acts, we don't restrict ourselves to those that serve our particular interests. Similarly, our private interests often differ from the public interest, but, despite our sentiments in favor of our self-interest, we often also retain our sentiment in favor of the public interest. Where these interests concur, we observe a sensible increase of the sentiment, so it must be the case that the interests of society are not entirely indifferent to us.

With that final nail in Hobbes' coffin, Hume turns to develop his account of the sources of morality. Though we often approve or disapprove of the actions of those remote from us in space and time, it is nonetheless true that, in considering the acts of (say) an Athenian statesman, the good he produced “affects us with a less lively sympathy,” even though we judge their “merit to be equally great” as the similar acts of our contemporaries. In such cases our judgment “corrects the inequalities of our internal emotions and perceptions; in like manner, as it preserves us from error, in the several variations of images, presented to our external senses” (EPM, 227). Adjustment and correction is necessary in both cases if we are to think and talk consistently and coherently.

“The intercourse of sentiments” that conversation produces is the vehicle for these adjustments, for it takes us out of our own peculiar positions. We begin to employ general language which, since it is formed for general use, “must be moulded on some general views … .” In so doing, we take up a “general” or “common point of view,” detached from our self-interested perspectives, to form “some general unalterable standard, by which we may approve or disapprove of characters and manners.” We begin to “speak another language” — the language of morals, which “implies some sentiment common to all mankind, which recommends the same object to general approbation, and makes every man, or most men, agree in the same opinion or decision concerning it. It also implies some sentiment, so universal and comprehensive as to extend to all mankind, and render the actions and conduct, even of the persons the most remote, an object of applause or censure, according as they agree or disagree with that rule of right which is established. These two requisite circumstances belong alone to the sentiment of humanity here insisted on” (EPM, 272). It is the extended or extensive sentiment of humanity — benevolence or sympathy — that for Hume is ultimately “the foundation of morals.”

But even if the social virtues move us from a perspective of self-interest to one more universal and extensive, it might appear that the individual virtues do not. But since these virtues also receive our approbation because of their usefulness, and since “these advantages are enjoyed by the person possessed of the character, it can never be self-love which renders the prospect of them agreeable to us, the spectators, and prompts our esteem and approbation” (EPM, 234).

Just as we make judgments about others, we are aware, from infancy, that others make judgments about us. We desire their approval and modify our behavior in response to their judgments. This love of fame gives rise to the habit of reflectively evaluating our own actions and character traits. We first see ourselves as others see us, but eventually we develop our own standards of evaluation, keeping “alive all the sentiments of right and wrong,” which “begats, in noble natures, a certain reverence” for ourselves as well as others, “which is the surest guardian of every virtue” (EPM, 276). The general character of moral language, produced and promoted by our social sympathies, permits us to judge ourselves and others from the general point of view, the proper perspective of morality. For Hume, that is “…the most perfect morality with which we are acquainted” (EPM, 276).

Hume summarizes his account in this definition of virtue , or Personal Merit : “every quality of the mind, which is useful or agreeable to the person himself or to others , communicates a pleasure to the spectator, engages his esteem, and is admitted under the honourable denomination of virtue or merit” (EPM, 277). That is, as observers — of ourselves as well as others — to the extent that we regard certain acts as manifestations of certain character traits, we consider the usual tendencies of acts done from those traits, and find them useful or agreeable, to the agent or to others, and approve or disapprove of them accordingly. A striking feature of this definition is its precise parallel to the two definitions of cause that Hume gave as the conclusion of his central argument in the first Enquiry . Both definitions pick out features of events, and both record a spectator's reaction or response to those events.

Hume's “Advertisement” for the first two books of the Treatise promised subsequent works on morals, politics and criticism, but his Political Discourses , “Of Tragedy,” and “Of the Standard of Taste” are our only hints as to what he might have said about those topics.

Hume's political essays range widely, covering not only the constitutional issues one might expect, but also venturing into what we now call economics, dealing with issues of commerce, luxury, and their implications for society. His treatments of these scattered topics exhibit a unity of purpose and method that makes the essays much more than the sum of their parts, and links them not only with his more narrowly philosophical concerns, but also with his earlier moral and literary essays.

Adopting a causal, descriptive approach to the problems he discusses, Hume stresses that current events and concerns are best understood by tracing them historically to their origins. This approach contrasts sharply with contemporary discussions, which treated these events as the products of chance, or — worse — of providence. Hume substitutes a concern for the “moral causes” — the human choices and actions — of the events, conditions, or institutions he considers. This thoroughly secular approach is accentuated by his willingness to point out the bad effects of superstition and enthusiasm on society, government, and political and social life.

“Of the Standard of Taste” is a rich contribution to the then-emerging discipline of what we now call aesthetics . This complex essay contains a lucid statement of Hume's views on what constitutes “just criticism,” but it is not just about criticism, as some readers are beginning to realize. Though Hume's account of aesthetic judgment precisely parallels his account of causal and moral judgment, the essay also contains a discussion of how a naturalistic theory might deal with questions of normativity, and so is important, not just as a significant contribution to Hume's overall view, but also for its immediate relevance for problems in contemporary empirical naturalism.

Hume's History of England , published in six volumes over as many years in the 1750s, recalls his characterization, in the first Enquiry , of history as “so many collections of experiments.” Hume not surprisingly rejects the theoretical commitments of both Tory and Whig accounts of British history, and offers what he believes is an impartial account that looks at political institutions as historical developments responsive to Britons' experience of changing conditions, evaluating political decisions in the contexts in which they were made, instead of second-guessing them in the light of subsequent developments.

The Natural History of Religion is also a history in a sense, though it has been described as “philosophical” or “conjectural” history. It is an account of the origins and development of religious beliefs, with the thinly-disguised agenda of making clear not only the nonrational origins of religion, but also of exposing and describing the pathology of its current forms. Religion began in the postulation, by primitive peoples, of “invisible intelligences” to account for frightening, uncontrollable natural phenomena, such as disease and earthquakes. In its original forms, it was polytheistic, which Hume regards as relatively harmless because of its tolerance of diversity. But polytheism eventually gives way to monotheism, when the followers of one deity hold sway over the others. Monotheism is dogmatic and intolerant; worse, it gives rise to theological systems which spread absurdity and intolerance, but which use reason to corrupt philosophical thought. But since religion is not universal in the way that our nonrational beliefs in causation or physical objects are, perhaps it can eventually be dislodged from human thinking altogether.

Hume's Natural History cemented his reputation as a religious sceptic and an atheist, even before its publication. Prompted by his own prudence, as well as the pleas of his friends, he resisted publishing the Dialogues concerning Natural Religion , which he had worked on since the early 1750s, though he continued revising the manuscript until his death. An expansion and dramatic revision of the argument previewed in Section XI of the first Enquiry , the Dialogues are so riddled with irony that controversy still rages as to what character, if any, speaks for Hume. But his devastating critique of the argument from design leaves no doubt that — scholarly details about its enigmatic final section aside — the conclusions philosophers and theologians have drawn from that argument go far beyond any evidence the argument itself provides.

A fitting conclusion to a philosophical life, the posthumously published Dialogues would alone insure the philosophical and literary immortality of their author. In this magnificent work, Hume demonstrates his mastery of the dialogue form, while producing what many regard as the preeminent work in the philosophy of religion.

Bibliography

The abbreviations and texts cited above are as follows:

Other works by Hume and editions of Hume's writings are:

• Dialogues concerning Natural Religion , edited by Norman Kemp Smith, Oxford: Oxford University Press, 1935
• The Natural History of Religion , edited by H. E. Root, Stanford: Stanford University Press, 1967
• Essays, Moral, Political, Literary , edited by Eugene F. Miller, Indianapolis: Liberty Classics, 1985
• The History of England , edited by William B. Todd, Indianapolis: Liberty Classics, 1983

In addition to the letters found in [HL], Hume's correspondence may be found in:

• New Letters of David Hume , edited by Raymond Klibansky and Ernest C. Mossner, Oxford: Clarendon Press, 1954

Finally, the closest thing at present to a complete edition remains that of Green and Grose:

• The Philosophical Works of David Hume , edited by T. H. Green and T. H. Grose. 4 volumes, London: Longman, Green, 1874-75

A useful bibliography of work on Hume is:

• Hall, Roland. Fifty Years of Hume Scholarship: A Bibliographical Guide , Edinburgh: Edinburgh University Press, 1978
• Hall also prepared annual bibliographies of the Hume literature for Hume Studies , a journal specializing in work on Hume, for the years 1977-1986; these bibliographies appeared in the November issues of that journal from 1978 to 1988
• Hume Studies revived the practice of including bibliographies with its November 1994 issue, which contained a comprehensive bibliography of the Hume literature from 1986-1993 by William Edward Morris. Subsequent volumes contain annual supplements to this bibiliography, also by Morris
• Árdal, Páll S. Passion and Value in Hume's Treatise, Edinburgh: Edinburgh University Press, 1966; 2nd edition, revised, 1989
• Baier, Annette C. A Progress of Sentiments: Reflections on Hume's Treatise, Cambridge: Harvard University Press, 1991
• Beauchamp, Tom L. and Alexander Rosenberg. Hume and the Problem of Causation , New York: Oxford University Press, 1981
• Bennett, Jonathan. Learning from Six Philosophers , Two Volumes, Oxford: Clarendon Press, 2001
• Bennett, Jonathan. Locke, Berkeley, Hume: Central Themes , Oxford: Oxford University Press, 1971
• Blackburn, Simon. Essays in Quasi-Realism , New York: Oxford University Press, 1993
• Bricke, John. Hume's Philosophy of Mind , Princeton: Princeton University Press, 1980
• Box, Mark A. The Suasive Art of David Hume , Princeton: Princeton University Press, 1990
• Buckle, Stephen. Hume's Enlightenment Tract: The Unity and Purpose of An Enquiry concerning Human Understanding, Oxford: Clarendon Press, 2001
• Capaldi, Nicholas. Hume's Place in Moral Philosophy , New York: Peter Lang, 1989
• Dicker, Georges. Hume's Epistemology and Metaphysics: An Introduction , London and New York: Routledge, 1998
• Earman, John. Hume's Abject Failure: The Argument Against Miracles , New York: Oxford University Press, 2000
• Fodor, Jerry A. Hume Variations , Oxford: Clarendon Press, 2003
• Fogelin, Robert J. A Defense of Hume on Miracles , Princeton: Princeton University Press, 2003
• Fogelin, Robert J. Hume's Scepticism in the Treatise of Human Nature, London: Routledge and Kegan Paul, 1985
• Frasca-Spada, Marina. Space and the Self in Hume's Treatise, Cambridge: Cambridge University Press, 1998
• Frasca-Spada, Marina and Peter J. E. Kail (eds.) Impressions of Hume , Oxford: Clarendon Press, 2005
• Garrett, Don. Cognition and Commitment in Hume's Philosophy , Oxford/New York: Oxford University Press, 1996
• Harris, James A. Of Liberty and Necessity: The Free Will Debate in Eighteenth-Century British Philosophy , Oxford: Clarendon Press, 2005
• Jones, Peter. Hume's Sentiments , Edinburgh: Edinburgh University Press, 1982
• Livingston, Donald W. Philosophical Melancholy and Delirium: Hume's Pathology of Philosophy , Chicago: University of Chicago Press, 1998
• Livingston, Donald W. Hume's Philosophy of Common Life , Chicago: University of Chicago Press, 1984
• Loeb, Louis E. Stability and Justification in Hume's Treatise, New York: Oxford University Press, 2002
• Millican, Peter (ed.) Reading Hume on Human Understanding , Oxford: Clarendon Press, 2002
• Mossner, Ernest Campbell. The Life of David Hume , London: Nelson, 1954
• Noonan, Harold W. Hume on Knowledge , London and New York: Routledge, 1999
• Norton, David Fate (ed.) The Cambridge Companion to Hume , Cambridge: Cambridge University Press, 1993
• Norton, David Fate. David Hume, Common Sense Moralist, Sceptical Metaphysician , Princeton: Princeton University Press, 1982
• Noxon, James. Hume's Philosophical Development , Oxford: Oxford University Press, 1973
• Owen, David. Hume's Reason , Oxford: Oxford University Press, 2000.
• Passmore, John. Hume's Intentions , Cambridge: Cambridge University Press, 1952
• Pears, David. Hume's System , Oxford: Oxford University Press, 1990
• Penelhum, Terence. Themes in Hume: The Will, The Self, Religion , Oxford Clarendon Press, 2000
• Penelhum, Terence. Hume , London: Macmillan, 1975
• Price, H. H. Hume's Theory of the External World , Oxford: Clarendon Press, 1940
• Radcliffe, Elizabeth S. A Companion to Hume , Oxford: Blackwell, 2007
• Read, Rupert and Kenneth A. Richman. The New Hume Debate , New York and London: Routledge, 2000
• Russell, Paul. Freedom and Moral Sentiment , New York: Oxford University Press, 1995
• Smith, Norman Kemp. The Philosophy of David Hume , London: Macmillan, 1941
• Stanistreet, Paul. Hume's Scepticism and the Science of Human Nature , Aldershot: Ashgate, 2002
• Stewart, John B. Opinion and Reform in Hume's Political Philosophy , Princeton: Princeton University Press, 1992
• Stewart, M. A. and John P. Wright. Hume and Hume's Connexions , Edinburgh: Edinburgh University Press, 1994
• Strawson, Galen. The Secret Connexion: Causation, Realism and David Hume , Oxford: Oxford University Press, 1989
• Stroud, Barry. Hume , London: Routledge and Kegan Paul, 1977
• Traiger, Saul. The Blackwell Guide to Hume's Treatise, Oxford: Blackwell, 2006
• Tweyman, Stanley. David Hume: Critical Assessments , Six Volumes, London and New York: Routledge, 1995
• Waxman, Wayne. Hume's Theory of Consciousness , Cambridge: Cambridge University Press, 1994
• Wright, John P. The Sceptical Realism of David Hume , Minneapolis: University of Minnesota Press, 1983
• The Leeds Hume Project , University of Leeds
• The Hume Society , based at the Philosophy Department, University of Iceland
• David Hume page , by Bill Uzgalis (Philosophy/Oregon State University), including links to texts of the Enquiry
• Ty's Hume Homepage , maintained by D. Tycerium Lightner
• Hume's Life and Writings
• Hume's Metaphysical and Epistemological Theories
• Hume's Moral Theories
• Hume's Writings on Religion
• Hume's Essays : Moral, Political, and Literary

Berkeley, George | Hobbes, Thomas | Hume, David: Newtonianism and Anti-Newtonianism | Locke, John | miracles

Acknowledgment

The editors would like to thank Gintautas Miliauskas (Vilnius University) for notifying us of several typographical errors in this entry.

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The first amendment, historic document, an essay concerning human understanding (1690).

John Locke | 1690

John Locke (1632-1704) was the author of A Letter Concerning Toleration (1689), An Essay concerning Human Understanding (1690), Two Treatises on Government (1690), and other works. Prior to the American Revolution, Locke was best known in America for his epistemological work. Contrary to the Cartesian view of innate ideas, Locke claimed that the human mind is a tabula rasa and that knowledge is accessible to us through sense perception and experience. Of the significance of Locke’s contribution to the theory of knowledge, James Madison compared him to Sir Isaac Newton’s discoveries in natural science: Both established “immortal systems, the one [Newton] in matter, the other [Locke] in mind” ("Spirit of Governments," 1791). 

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Professor of History and Charles O. Lee and Louise K. Lee Chair in the Western Heritage at Hillsdale College

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CHAP. II.: No Innate Principles in the Mind.

The way shewn how we come by any knowledge, sufficient to prove it not innate.

§ 1. It is an established opinion amongst some men, that there are in the understanding certain innate principles; some primary notions, ϰοιναὶ ἔννοιαι, characters, as it were, stamped upon the mind of man, which the soul receives in its very first being; and brings into the world with it. It would be sufficient to convince unprejudiced readers of the falseness of this supposition, if I should only shew (as I hope I shall in the following parts of this discourse) how men, barely by the use of their natural faculties, may attain to all the knowledge they have, without the help of any innate impressions; and may arrive at certainty, without any such original notions or principles. For I imagine any one will easily grant, that it would be impertinent to suppose, the ideas of colours innate in a creature, to whom God hath given sight, and a power to receive them by the eyes, from external objects: and no less unreasonable would it be to attribute several truths to the impressions of nature, and innate characters, when we may observe in ourselves faculties, fit to attain as easy and certain knowledge of them, as if they were originally imprinted on the mind. . . .

CHAP. I: Of Idea in general, and their Original.

§ 2. Let us then suppose the mind to be, as we say, white paper, void of all characters, without any ideas: —How comes it to be furnished? Whence comes it by that vast store which the busy and boundless fancy of man has painted on it with an almost endless variety? Whence has it all the materials of reason and knowledge? To this I answer, in one word, from EXPERIENCE. In that all our knowledge is founded, and from that it ultimately derives itself. Our observation employed either, about external sensible objects, or about the internal operations of our minds perceived and reflected on by ourselves, is that which supplies our understandings with all the materials of thinking. These two are the fountains of knowledge, from whence all the ideas we have, do spring. . . .

CHAP. XI.: Of Discerning, and other Operations of the Mind.

§ 17. I pretend not to teach, but to inquire, and therefore cannot but confess here again, that external and internal sensation are the only passages that I can find of knowledge to the understanding. These alone, as far as I can discover, are the windows by which light is let into this dark room: for methinks the understanding is not much unlike a closet wholly shut from light, with only some little opening left, to let in external visible resemblances, or ideas of things without: would the pictures coming into such a dark room but stay there, and lie so orderly as to be found upon occasion, it would very much resemble the understanding of a man, in reference to all objects of sight, and the ideas of them. . . .

CHAP. XXI.: Of Power.

§ 51. As therefore the highest perfection of intellectual nature lies in a careful and constant pursuit of true and solid happiness, so the care of ourselves, that we mistake not imaginary for real happiness, is the necessary foundation of our liberty. The stronger ties we have to an unalterable pursuit of happiness in general, which is our greatest good, and which, as such, our desires always follow, the more are we free from any necessary determination of our will to any particular action, and from a necessary compliance with our desire, set upon any particular, and then appearing preferable good, till we have duly examined, whether it has a tendency to, or be inconsistent with our real happiness: and therefore till we are as much informed upon this inquiry, as the weight of the matter, and the nature of the case demands; we are, by the necessity of preferring and pursuing true happiness as our greatest good, obliged to suspend the satisfaction of our desires in particular cases.

§ 52. This is the hinge on which turns the liberty of intellectual beings, in their constant endeavours after and a steady prosecution of true felicity, that they can suspend this prosecution in particular cases, till they have looked before them, and informed themselves whether that particular thing, which is then proposed or desired, lie in the way to their main end, and make a real part of that which is their greatest good: for the inclination and tendency of their nature to happiness is an obligation and motive to them, to take care not to mistake or miss it; and so necessarily puts them upon caution, deliberation, and wariness, in the direction of their particular actions, which are the means to obtain it. Whatever necessity determines to the pursuit of real bliss, the same necessity with the same force establishes suspense, deliberation, and scrutiny of each successive desire, whether the satisfaction of it does not interfere with our true happiness, and mislead us from it. This, as seems to me, is the great privilege of finite intellectual beings; and I desire it may be well considered, whether the great inlet and exercise of all the liberty men have, are capable of, or can be useful to them, and that whereon depends the turn of their actions, does not lie in this, that they can suspend their desires, and stop them from determining their wills to any action, till they have duly and fairly examined the good and evil of it, as far forth as the weight of the thing requires.

 § 2. . . . Sense and intuition reach but a very little way. The greatest part of our knowledge depends upon deductions and intermediate ideas: and in those cases, where we are fain to substitute assent instead of knowledge, and take propositions for true, without being certain they are so, we have need to find out, examine, and compare the grounds of their probability. In both these cases, the faculty which finds out the means, and rightly applies them to discover certainty in the one, and probability in the other, is that which we call reason. For as reason perceives the necessary and indubitable connexion of all the ideas or proofs one to another, in each step of any demonstration that produces knowledge: so it likewise perceives the probable connexion of all the ideas or proofs one to another, in every step of a discourse, to which it will think assent due. This is the lowest degree of that which can be truly called reason. . . .

§ 23. By what has been before said of reason, we may be able to make some guess at the distinction of things, into those that are according to, above, and contrary to reason. 1. According to reason are such propositions, whose truth we can discover by examining and tracing those ideas we have from sensation and reflection; and by natural deduction find to be true or probable. 2. Above reason are such propositions, whose truth or probability we cannot by reason derive from those principles. 3. Contrary to reason are such propositions, as are inconsistent with, or irreconcileable to, our clear and distinct ideas. Thus the existence of one God is according to reason; the existence of more than one God, contrary to reason; the resurrection of the dead, above reason. . . .

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John Locke (1689)

An Essay concerning Human Understanding.

Source : An Essay Concerning Human Understanding (1689). 38th Edition from William Tegg, London; scanned in three separate excerpts from early in the work.

CHAPTER II NO INNATE PRINCIPLES IN THE MIND.

1. The way shown how we come by any knowledge, sufficient to prove it not innate. – It is an established opinion among some men, that there are in the understanding certain innate principles; some primarily notions, characters, as it were, stamped upon the mind of man, which the soul receives in its very first being and brings into the world with it. It would be sufficient to convince unprejudiced readers of the falseness of this supposition, if I should only show (as I hope I shall in the following parts of this discourse) how men, barely by the use of their natural faculties, may attain to all the knowledge they have, without the help of any innate impressions, and may arrive at certainty without any such original notions or principles. For I imagine, any one will easily grant, that it would be impertinent to suppose the ideas of colours innate in a creature to whom God hath given sight, and a power to receive them by the eyes from external objects: and no less unreasonable would it be to attribute several truths to the impressions of nature and innate characters, when we may observe in ourselves faculties fit to attain as easy and certain knowledge of them as if they were originally imprinted on the mind.

But because a man is not permitted without censure to follow his own thoughts in the search of truth, when they lead him ever so little out of the common road, I shall set down the reasons that made me doubt of the truth of that opinion as an excuse for my mistake, if I be in one; which I leave to be considered by those who, with me, dispose themselves to embrace truth wherever they find it.

2. General assent the great argument. – There is nothing more commonly taken for granted, than that there are certain principles, both speculative and practical (for they speak of both), universally agreed upon by all mankind; which therefore; they argue, must needs be constant impressions which the souls of men receive in their first beings, and which they bring into the world with them, as necessarily and really as they do any of their inherent faculties.

3. Universal consent proves nothing innate. - This argument, drawn from universal consent, has this misfortune in it, that if it were true in matter of fact that there were certain truths wherein all mankind agreed, it would not prove them innate, if there can be any other way shown, how men may come to that universal agreement in the things they do consent in; which I presume may be done.

4. “What is, is;” and, “It is impossible for the same thing to be, and not to be,” not universally assented to. – But, which is worse, this argument of universal consent, which is made use of to prove innate principles, seems to me a demonstration that there are none such; because there are none to which all mankind give an universal assent. I shall begin with the speculative, and instance in those magnified principles of demonstration: “Whatsoever is, is; ” and “It is impossible for the same thing to be, and not to be,” which, of all others, I think, have the most allowed title to innate. These have so settled a reputation of maxims universally received that it will, no doubt, be thought strange if any one should seem to question it. But yet I take liberty to say, that these propositions are so far from having an universal assent, that there are a great part of mankind to whom they are not so much as known.

5. Not on the mind naturally, imprinted, because not known to children, idiots, etc. – For, first, it is evident, that all children and idiots have not the least apprehension or thought of them; and the want of that is enough to destroy that universal assent, which must needs be the necessary concomitant of all innate truths: it seeming to me near a contradiction to say, that there are truths imprinted on the soul which it perceives or understands not; imprinting, if it signify anything, being nothing else but the making certain truths to be perceived. For to imprint anything on the mind without the mind’s perceiving it, seems to me hardly intelligible. If therefore children and idiots have souls, have minds, with those impressions upon them, they must unavoidably perceive them, and necessarily know and assent to these truths; Which, since they do not, it is evident that there are no such impressions. For if they are not notions naturally imprinted, how can they be innate? And if they are notions imprinted, how can they he unknown? To say, a notion is imprinted on the mind, and yet at the same time to say that the mind is ignorant of it, and never yet took notice of it, is to make this impression nothing. No proposition can he said to be in the mind which it never yet knew, which it was never yet conscious of. For if any one say, then, by the same reason, all propositions that are true, and the mind is capable ever of assenting to, may be said to be in the mind, and to the imprinted; since if any one can be said to be in the mind, which it never yet knew, it must be only because it is capable of knowing it; and so the mind is of all truths it ever shall know. Nay, thus truths may be imprinted on the mind which it never did, nor ever shall, know: for a man may live long and die at last in ignorance of many truths which his mind was capable of knowing, and that with certainty. So that if the capacity of knowing be the natural impression contended for, all the truths a man ever comes to know will, by this account, be every one of them innate: and this great point will amount to no more, but only to a very improper way of speaking; which, whilst it pretends to assert the contrary, says nothing different from those who deny innate principles. For nobody, I think, ever denied that the mind was capable of knowing several truths. The capacity, they say, is innate; the knowledge acquired. But then, to what end such contest for certain innate maxims? If truths can be imprinted on the understanding without being perceived I can see no difference there can be between any truths the mind is capable of knowing in respect of their original: they must all be innate, or all adventitious; in vain shall a man go about to distinguish them. He therefore that talks of innate notions in the understanding, cannot (if he intend thereby any distinct sort of truths) mean such truths to be in the understanding as it never perceived, and is yet wholly ignorant of. For if these words (“to be in the understanding”) have any propriety, they signify to be understood. So that, to be in the understanding and not to be understood; to be in the mind, and never to be perceived; is all one as to say, anything is, and is not, in the mind or understanding. If therefore these two propositions: “Whatsoever is, is;” and, “It is impossible for the same thing to be, and not to be,” are by nature imprinted, children cannot be ignorant of them; infants, and all that have souls, must necessarily have them in their understandings, know the truth of them, and assent to it.

6. That men know them when they come to the use of reason, answered. – To avoid this, it is usually answered, that all well know and assent to them, when they come to the use of reason; and this is enough to prove them innate. I answer,

7. Doubtful expressions, that have scarce any signification, go for clear results to those who, being prepossessed, take not the pains to examine even what they themselves say. For, to apply this answer with any tolerable sense to our present purpose, it must signify one of these two things; either, that, as soon as men come to the use of reason, these supposed native inscriptions come to be known and observed by them; or else, that the use and exercise of men’s reasons assists them in the discovery of these principles, and certainly makes them known to them.

8. If reason discovered them, that would not prove them innate. – If they mean that by the use of reason men may discover these principles, and that this is sufficient to prove them innate, their way of arguing will stand thus: viz. That, whatever truths reason can certainly discover to us and make us firmly assent to, those are all naturally imprinted on the mind; since that universal assent which is made the mark of them, amounts to no more but this – that by the use of reason we are capable to come to a certain knowledge of, and assent to, them; and by this means there will be no difference between the maxims of the mathematicians and theorems they deduce from them: all must be equally allowed innate, they being all discoveries made by the use of reason and truths that a rational creature may certainly come to know, if he apply his thoughts rightly that way.

9. It is false that reason discovers them. – But how can these men think the use of reason necessary to discover principles that are supposed innate, when reason (if we may believe them) is nothing else but the faculty of deducing unknown truths from principles or propositions that are already known? That certainly can never be thought innate which we have need of reason to discover, unless, as I have said, we will have all the certain truths that reason ever teaches us to be innate. We may as well think the use of reason necessary to make our eyes discover visible objects as that there should be need of reason, or the exercise thereof to make the understanding see what is originally engraved in it, and cannot be in the understanding before it be perceived by it. So that to make reason discover these truths thus imprinted, is to say, that the use of reason discovers to a man what he knew before; and if men have those innate impressed truths originally, and before the use of reason and yet are always ignorant of them till they come to the use of reason, it is in effect to say that men know, and know them not, at the same time.

10. It will here perhaps be said, that mathematical demonstrations, and other truths that are not innate, are not assented to, as soon as proposed, wherein they are distinguished from these maxims and other innate truths. I shall have occasion to speak of assent upon the first proposing, more particularly by and by. I shall here only, and that very readily, allow, that these maxims and mathematical demonstrations are in this different – that the one has need of reason using of proofs to make them out and to gain our assent; but the other, as soon as understood, are, without any the least reasoning, embraced and assented to. But I withal beg leave to observe, that it lays open the weakness of this subterfuge which requires the use of reason for the discovery of these general truths, since it must be confessed, that in their discovery there is no use made of reasoning at all. And I think those who give this answer will not be forward to affirm, that the knowledge of this maxim, “That it is impossible for the same thing to be, and not to be,” is a deduction of our reason. For this would be to destroy that bounty of nature they seem so fond of, whilst they make the knowledge of those principles to depend on the labour of our thoughts; for all reasoning is search and casting about, and requires pains and application. ...

BOOK II, CHAPTER I: OF IDEAS IN GENERAL, AND THEIR ORIGINAL.

l. Idea is the object of thinking. – Every man being conscious to himself, that he thinks, and that which his mind is applied about, whilst thinking, being the ideas that are there, it is past doubt that men have in their mind several ideas, such as are those expressed by the words, “whiteness, hardness, sweetness, thinking, motion, man, elephant, army, drunkenness,” and others. It is in the first place then to be inquired, How he comes by them? I know it is a received doctrine, that men have native ideas and original characters stamped upon their minds in their very first being. This opinion I have at large examined already; and, I suppose, what I have said in the foregoing book will be much more easily admitted, when I have shown whence the understanding may get all the ideas it has, and by what ways and degrees they may come into the mind; for which I shall appeal to every one’s own observation and experience.

2. All ideas come from sensation or reflection. – Let us then suppose the mind to be, as we say, white paper [ tabula rasa ], void of all characters without any ideas; how comes it to be furnished? Whence comes it by that vast store, which the busy and boundless fancy of man has painted on it with an almost endless variety? Whence has it all the materials of reason and knowledge? To this I answer, in one word, From experience: in that all our knowledge is founded, and from that it ultimately derives itself. Our observation, employed either about external sensible objects, or about the internal operations of our minds, perceived and reflected on by ourselves is that which supplies our understandings with all the materials of thinking. These two are the fountains of knowledge, from whence all the ideas we have, or can naturally have, do spring.

3. The object of sensation one source of ideas. – First. Our senses, conversant about particular sensible objects, do convey into the mind several distinct perceptions of things, according to those various ways wherein those objects do affect them; and thus we come by those ideas we have of yellow, white, heat, cold, soft, hard, bitter, sweet, and all those which we call sensible qualities; which when I say the senses convey into the mind, I mean, they from external objects convey into the mind what produces there those perceptions. This great source of most of the ideas we have, depending wholly upon our senses, and derived by them to the understanding, I call, “sensation.”

4. The operations of our minds the other source of them. – Secondly. The other fountain, from which experience furnisheth the understanding with ideas, is the perception of the operations of our own minds within us, as it is employed about the ideas it has got; which operations, when the soul comes to reflect on and consider, do furnish the understanding with another set of ideas which could not be had from things without and such are perception, thinking, doubting, believing, reasoning, knowing, willing, and all the different actings of our own minds; which we, being conscious of, and observing in ourselves, do from these receive into our understandings as distinct ideas, as we do from bodies affecting our senses. This source of ideas every man has wholly in himself; and though it be not sense as having nothing to do with external objects, yet it is very like it, and might properly enough be called “internal sense.” But as I call the other “sensation,” so I call this “reflection,” the ideas it affords being such only as the mind gets by reflecting on its own operations within itself. By reflection, then, in the following part of this discourse, I would be understood to mean that notice which the mind takes of its own operations, and the manner of them, by reason whereof there come to be ideas of these operations in the understanding. These two, I say, viz., external material things as the objects of sensation, and the operations of our own minds within as the objects of reflection, are to me, the only originals from whence all our ideas take their beginnings. The term “operations” here, I use in a large sense, as comprehending not barely the actions of the mind about its ideas, but some sort of passions arising sometimes from them, such as is the satisfaction or uneasiness arising from any thought.

5. All our ideas are of the one or the other of these. – The understanding seems to me not to have the least glimmering of any ideas which it doth not receive from one of these two. External objects furnish the mind with the ideas of sensible qualities, which are all those different perceptions they produce in us; and the mind furnishes the understanding with ideas of its own operations.

These, when we have taken a full survey of them, and their several modes, combinations, and relations, we shall find to contain all our whole stock of ideas, and that we have nothing in our mind which did not come in one of these two ways. Let anyone examine his own thoughts; and thoroughly search into his understanding, and then let him tell me, whether all the original ideas he has there, are any other than of the objects of his senses, or of the operations of his mind considered as objects of his reflection; and how great a mass of knowledge soever he imagines to be lodged there, he will, upon taking a strict view see that he has not any idea in his mind but what one of these two have imprinted, though perhaps with infinite variety compounded and enlarged by the understanding, as we shall see hereafter.

6. Observable in children. – He that attentively considers the state of a child at his first coming into the world, will have little reason to think him stored with plenty of ideas that are to be the matter of his future knowledge. It is by degrees he comes to be furnished with them; and though the ideas of obvious and familiar qualities imprint themselves before the memory begins to keep a register of time and order, yet it is often so late before some unusual qualities come in the way, that there are few men that cannot recollect the beginning of their acquaintance with them: and, if it were worth while, no doubt a child might be so ordered as to have but a very few even of the ordinary ideas till he were grown up to a man. But all that are born into the world being surrounded with bodies that perpetually and diversely affect them, variety of ideas whether care be taken about it, or no, are imprinted on the minds of children. Light and colours are busy at hand every where when the eye is but open; sounds and some tangible qualities fail not to solicit their proper senses and force an entrance to the mind; but yet I think it will be granted easily, that if a child were kept in a place where he never saw any other but black and white till he were a man, he would have no more ideas of scarlet or green, than he that from his childhood never tasted an oyster or a pine-apple has of those particular relishes.

7. Men are differently furnished with these according to the different objects they converse with. – Men then come to be furnished with fewer or more simple ideas from without, according as the objects they converse with afford greater or less variety; and from the operations of their minds within, according as they more or less reflect on them. For, though he that contemplates the operations of his mind cannot but have plain and clear ideas of them; yet, unless he turn his thoughts that way, and considers them attentively, he will no more have clear and distinct ideas of all the operations of his mind, and all that may be observed therein than he will have all the particular ideas of any landscape or of the parts and motions of a clock, who will not turn his eyes to it, and with attention heed all the parts of it. The picture or clock may be so placed, that they may come in his way every day; but yet he will have but a confused idea of all the parts they are made of, till he applies himself with attention to consider them each in particular. ...

CHAPTER III: OF IDEAS OF ONE SENSE

l. Division of simple ideas. – The better to conceive the ideas we receive from sensation, it may not be amiss for us to consider them in reference to the different ways whereby they make their approaches to our minds, and make themselves perceivable by us.

First, then, there are some which come into our minds by one sense only.

Secondly. There are others that convey themselves into the mind by more senses than one.

Thirdly. Others first are had from reflection only.

Fourthly. There are some that make themselves way, and are suggested to the mind, by all the ways of sensation and reflection.

We shall consider them apart under these several heads.

1. There are some ideas which have admittance only through one sense, which is peculiarly adapted to receive them. Thus light and colours, as white, red, yellow, blue, with their several degrees or shades and mixtures, as green, scarlet, purple, sea-green, and the rest, come in only by the eyes; all kinds of noises, sounds, and tones, only by the ears; the several tastes and smells, by the nose and palate. And if these organs, or the nerves which are the conduits to convey them from without to their audience in the brain, the mind’s presence-room, (as I may so call it,) are, any of them, so disordered as not to perform their functions, they have no postern to be admitted by, no other way to bring themselves into view, and be received by the understanding.

The most considerable of those belonging to the touch are heat and cold, and solidity; all the rest – consisting almost wholly in the sensible configuration, as smooth and rough; or else more or less firm adhesion of the parts, as hard and soft, tough and brittle – are obvious enough.

2. I think it will be needless to enumerate all the particular simple ideas belonging to each sense. Nor indeed is it possible it we would, there being a great many more of them belonging to most of the senses than we have names for. The variety of smells, which are as many almost, if not more, than species of bodies in the world, do most of them want name. Sweet and stinking commonly serve our turn for these ideas, which in effect is little more than to call them pleasing or displeasing; though the smell of a rose and violet, both sweet, are certainly very distinct ideas. Nor are the different tastes that by, our palates we receive ideas of, much better provided with names. Sweet, bitter, sour, harsh , and salt , are almost all the epithets we have to denominate that numberless variety of relishes which are to be found distinct, not only in almost every sort of creatures but in the different parts of the same plant, fruit, or animal. The same may be said of colours and sounds. I shall therefore, in the account of simple ideas I am here giving, content myself to set down only such as are most material to our present purpose, or are in themselves less apt to be taken notice of, though they are very frequently the ingredients of our complex ideas; amongst which I think I may well account “solidity” which therefore I shall treat of in the next chapter.

Further Reading: Biography | Descartes (Rationalism) | Berkeley (Subjective Idealism) |

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The Cambridge Companion to Locke's 'Essay Concerning Human Understanding'

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First published in 1689, John Locke's Essay Concerning Human Understanding is widely recognised as among the greatest works in the history of Western philosophy. The Essay puts forward a systematic empiricist theory of mind, detailing how all ideas and knowledge arise from sense experience. Locke was trained in mechanical philosophy and he crafted his account to be consistent with the best natural science of his day. The Essay was highly influential and its rendering of empiricism would become the standard for subsequent theorists. This Companion volume includes fifteen new essays from leading scholars. Covering the major themes of Locke's work, they explain his views while situating the ideas in the historical context of Locke's day and often clarifying their relationship to ongoing work in philosophy. Pitched to advanced undergraduates and graduate students, it is ideal for use in courses on early modern philosophy, British empiricism and John Locke.

'This is not only an immensely valuable and stimulating collection of essays, but also a beautifully edited and produced one, with an elegant and readable typeface, no typographical errors, and a very extensive bibliography. All Locke specialists should possess a copy and all teachers of Locke should include it on their students' reading lists.'

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Frontmatter pp i-xiv

• Get access Check if you have access via personal or institutional login Log in Register

Introduction pp 1-6

• By Lex Newman

1 - The Intellectual Setting and Aims of the Essay pp 7-32

• By G. A. J. Rogers

2 - Locke’s Polemic against Nativism pp 33-66

• By Samuel C. Rickless

3 - The Taxonomy of Ideas in Locke’s Essay pp 67-100

• By Martha Brandt Bolton

4 - Locke’s Distinctions between Primary and Secondary Qualities pp 101-129

• By Michael Jacovides

5 - Power in Locke’s Essay pp 130-156

• By Vere Chappell

6 - Locke on Substance pp 157-191

• By Edwin McCann

7 - Locke on Ideas of Identity and Diversity pp 192-230

• By Gideon Yaffe

8 - Locke on Ideas and Representation pp 231-257

• By Thomas M. Lennon

9 - Locke on Essences and Classification pp 258-285

• By Margaret Atherton

10 - Language, Meaning, and Mind in Locke’s Essay pp 286-312

• By Michael Losonsky

11 - Locke on Knowledge pp 313-351

12 - locke’s ontology pp 352-380.

• By Lisa Downing

13 - The Moral Epistemology of Locke’s Essay pp 381-405

• By Catherine Wilson

14 - Locke on Judgment pp 406-435

• By David Owen

15 - Locke on Faith and Reason pp 436-455

• By Nicholas Jolley

Bibliography pp 456-472

Index of names and subjects pp 473-478, index of passages cited pp 479-486, full text views.

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• An Essay Concerning Human Understanding
• Literature Notes
• About An Essay Concerning Human Understanding
• Book Summary
• Summary and Analysis
• Book I: Innate Ideas
• Book II: Of Ideas, Chapters 1-11
• Book II: Of Ideas, Chapters 12-33
• Book III: Of Words
• Book IV: Knowledge and Probability
• John Locke Biography
• Full Glossary for An Essay Concerning Human Understanding
• Essay Questions
• Cite this Literature Note

An Essay Concerning Human Understanding by John Locke is one of the great books of the Western world. It has done much to shape the course of intellectual development, especially in Europe and America, ever since it was first published in 1690. Few books have ever been written that have so adequately represented the spirit of an age or left so great an imprint on so many different fields of inquiry. Although the main subject matter of the Essay is primarily a philosophical one, it has had a direct bearing on such areas of thought as education, government, ethics, theology, and religion. Indeed, there are few disciplines in the field of higher education that have not been influenced to some extent by the ideas set forth in this monumental work.

The importance of the book is well indicated by the number of editions that have been published. Between the time of its first publication and the author's death, four editions had been printed, and since that time more than forty editions have been published. Scholars in each succeeding generation have become acquainted with its contents, and in many instances they have made replies in book form to the arguments presented in it.

Because the Essay deals with a subject that is of vital concern to every field of knowledge and because the author was held in high esteem by authors and men of affairs who were contemporary with him, the book became at once the subject of criticism and the occasion for many vigorous controversies. This was in a sense what Locke had hoped his writing would accomplish. He was not a dogmatist, and he made no pretense of possessing a store of wisdom to be passed on to others. Rather, his purpose was to stimulate others to think for themselves, and what he had to say was intended as a means toward that end. In fact, it was one of Locke's major ambitions in all of his writings to dispel the sources of intolerance and encourage people to promote the cause of freedom in their thinking as well as in their actions. Many of the freedoms of which we boast in the Western world today are due in no small measure to the work of this man.

Among the critics who have expressed their views about Locke's work in writing, one finds both praise and condemnation. This is due in part to the fact that not all of them have interpreted what he had to say in the same way. Each critic has viewed the work from the perspective of his own experience and understanding. Each one has come to it with his own presuppositions, and these have been bound to influence the judgments made concerning it. To some extent, this is an unavoidable procedure, and one must deal with it in the best way that he can.

The Essay Concerning Human Understanding was the first work of its kind to appear in modern times. It was an attempt on the part of the author to make a serious and systematic inquiry in the problems of epistemology. It marked an important beginning, for once the inquiry had been brought to the attention of a reputable group of scholars, it became the central issue in the philosophical discussions that took place during the next one and one-half centuries. In fact, the movement that began with Locke was continued by Berkeley, Leibnitz, and other writers of distinction. It reached in one sense a culmination in the philosophies of Hume and Kant.

After Kant, interest in epistemology was replaced to a considerable extent by other topics, which dominated the field until the early part of the twentieth century. After the close of the First World War, a new interest was developed in questions concerning the nature and limitations of human knowledge, and once more the problems that were discussed in Locke's book were given consideration by scholars who were working in many different areas of human experience. While it is true that many of Locke's conclusions are rejected by philosophers of the present time, the spirit of his inquiry may still be regarded as a dominant characteristic of the thinking of the present day.

Any adequate appreciation of Locke's work must take into account the circumstances under which the book was written, as well as the major objective that the author had in mind. Many of the criticisms that have been written about it appear to have overlooked one or both of these points. For example, it has been fairly common among Locke's critics to call attention to the fact that incongruities can be found among the different sections of his work. That instances of this kind can be found when one reads the entire book must be admitted by anyone who has read it with care. But at least a partial explanation for this fact can be seen in the way in which it was composed.

The Essay was not the product of a continuous period of writing. It was produced a little at a time over a period of more than twenty years. Obviously, some changes and modifications were bound to take place as Locke gave added consideration to the questions that were involved. Besides, he made it abundantly clear throughout the Essay that he had no intention of speaking the last or final word on the subject. All that he intended to do was to set down the best thoughts that had come to him at the time of his writing. This he did with the hope that it would stimulate others to carry on a similar inquiry in their own minds.

In an epistle to the reader which forms a kind of preface to the book, Locke tells us how it was that he became interested in this type of inquiry. It all began in a series of discussions that took place in the company of a small group of friends who had been meeting at regular intervals to exchange with one another their views on important questions of the day. Evidently the topics for discussion included such subjects as science, morals, religion, and their relation to one another and to other disciplines. The fact that the members of the group seldom reached any agreement among themselves and often failed to reach any definite conclusions at all caused him to wonder just what benefits, if any, these discussions might have. The more he thought about it, the clearer it became to him that any progress which might be achieved along these lines could come about only by giving careful consideration to the possibilities and the limitations of the human mind.

If one could find out what it is possible for human minds to know and what are those areas that cannot be known, then one need not waste time on those questions that cannot be answered. Again, it would be most helpful to find out those areas, if any, of which we can have certain or absolute knowledge, as well as those areas in which we can never obtain more than probable knowledge. It was the pursuit of these inquiries that led to the writing of the Essay. The task that he set out to accomplish was far more difficult than he was aware at first, and reflection on the issues involved over long periods of time led to many changes and modifications.

The Essay as a whole is a lengthy piece of work, and it is not unusual for those who read it at the present time to become lost in the detailed accounts that are included in it. Many of the words that are used are ambiguous in their meaning, and the ways in which they are used are not always consistent with one another. Further difficulties arise from the fact that words do not necessarily have the same meaning today that they did at the time when Locke wrote. His purpose was the very practical one of helping people to think more clearly about the problems of everyday living, and as a means toward this end he used language in the sense in which it was generally understood at that time.

Technicalities in connection with the use of language with which we are familiar at the present time were not recognized by the average reader in Locke's day, and this accounts for some of the misunderstandings that have occurred in connection with the interpretation of his writings on the part of more recent critics. But these difficulties are relatively minor and should in no way obscure the major objective that Locke had hoped to accomplish.

The primary purpose that seems to have inspired all of Locke's major writings was his intense devotion to the cause of human liberty. He was unalterably opposed to tyranny in any of the forms in which it had been manifested. This included not only political tyranny but moral and religious tyranny as well. The age in which he lived had witnessed the results of tyranny on the part of both political and religious institutions. In the field of government, tyranny had been supported by the theory of the divine right of kings. In a somewhat similar manner, the authority and prestige of the church had been used to coerce individuals into acceptance of what they were told to believe and to do. To all of these devices for controlling the minds and activities of men, Locke was opposed. His views found eloquent expression in his Treatises on Government and his Letters on Toleration. The same objective, although expressed in a more indirect fashion, can be attributed to the Essay Concerning Human Understanding.

Because the freedom of the individual to think and to act for himself necessarily entails a sense of responsibility to exercise these freedoms in the best possible manner, anything that would help to prepare people for this task would be in order. As Locke saw it, nothing would help them more in this respect than a better understanding of the processes that enable human minds to arrive at truth. Furthermore, an appreciation of the limitations of the human mind would encourage an attitude of tolerance toward individuals holding different and conflicting opinions. Tolerance in human society would tend to be a safeguard against persecution and the evils that are necessarily associated with it.

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The “blind spot” in science that’s fueling a crisis of meaning

• Science is the most powerful and successful form of objective knowledge gathering.
• However, we lack a comparable understanding of how our lived experiences are essential to all human knowledge.
• In the 2024 book  The Blind Spot,  Adam Frank, Marcelo Gleiser, and Evan Thompson argue that this conceptual disconnect between the observer and the observed is fueling a crisis of meaning.

Our scientific worldview has gotten stuck in an impossible contradiction, making our present crisis fundamentally a crisis of meaning. On the one hand, science appears to make human life seem ultimately insignificant. The grand narratives of cosmology and evolution present us as a tiny contingent accident in a vast indifferent Universe. On the other hand, science repeatedly shows us that our human situation is inescapable when we search for objective truth because we cannot step outside our human form and attain a God’s-eye view of reality. 

Cosmology tells us that we can know the Universe and its origin only from our inside position, not from the outside. We live within a causal bubble of information — the distance light traveled since the Big Bang — and we cannot know what lies outside. Quantum physics suggests that the nature of subatomic matter cannot be separated from our methods of questioning and investigating it. In biology, the origin and nature of life and sentience remain a mystery despite marvelous advances in genetics, molecular evolution, and developmental biology. Ultimately, we cannot forgo relying on our own experience of being alive when we seek to comprehend the phenomenon of life. Cognitive neuroscience drives the point home by indicating that we cannot fully fathom consciousness without experiencing it from within. 

Each of these fields ultimately runs aground on its own paradoxes of inner versus outer, and observer versus observed, that collectively turn on the conundrum of how to understand awareness and subjectivity in a Universe that was supposed to be fully describable in objective scientific terms without reference to the mind. The striking paradox is that science tells us both that we’re peripheral in the cosmic scheme of things and that we’re central to the reality we uncover. Unless we understand how this paradox arises and what it means, we’ll never be able to understand science as a human activity, and we’ll keep defaulting to a view of nature as something to gain mastery over. 

Each of the cases just mentioned — cosmology and the origin of the Universe, quantum physics and the nature of matter, biology and the nature of life, cognitive neuroscience and the nature of consciousness — represents more than an individual scientific field. Collectively they represent our culture’s grand scientific narratives about the origin and structure of the Universe and the nature of life and the mind. They underpin the ongoing project of a global scientific civilization. They constitute a modern form of mythos: They are the stories that orient us and structure our understanding of the world. 

For these reasons, the paradoxes these fields face are more than mere intellectual or theoretical puzzles. They signal the larger unreconciled perspectives of the knower and the known, mind and nature, subjectivity and objectivity, whose fracture menaces our project of civilization altogether. Our present-day technologies, which drive us ever closer to existential threats , concretize this split by treating everything — including, paradoxically, awareness and knowing themselves — as an objectifiable, informational quantity or resource. It’s precisely this split — the divorce between knower and known and the suppression of the knower in favor of the known — that constitutes our meaning crisis. The climate emergency, which arises from our treating nature as just a resource for our use, is the most pronounced and catastrophic manifestation of our crisis. 

In short, although we have created the most powerful and successful form of objective knowledge of all time, we lack a comparable understanding of ourselves as knowers. We have the best maps we’ve ever made, but we’ve forgotten to take account of the map makers. Unless we change how we navigate, we’re bound to head deeper into peril and confusion. 

[A]lthough we have created the most powerful and successful form of objective knowledge of all time, we lack a comparable understanding of ourselves as knowers. Adam Frank, Marcelo Gleiser, & Evan Thompson

We call the source of the meaning crisis the Blind Spot. At the heart of science lies something we do not see that makes science possible, just as the blind spot lies at the heart of our visual field and makes seeing possible. In the visual blind spot sits the optic nerve; in the scientific blind spot sits direct experience — that by which anything appears, shows up, or becomes available to us. It is a precondition of observation, investigation, exploration, measurement, and justification. Things appear and become available thanks to our bodies and their feeling and perceiving capacities. Direct experience is bodily experience. 

“The body is the vehicle of being in the world,” says French philosopher Maurice Merleau-Ponty, but first-hand bodily experience lies hidden in the Blind Spot. 

The tragedy the Blind Spot forces on us is the loss of what’s essential to human knowledge — our lived experience. The Universe and the scientist who seeks to know it become lifeless abstractions. Triumphalist science is actually humanless, even if it springs from our human experience of the world. This disconnection between science and experience, the essence of the Blind Spot, lies at the heart of the many challenges and dead ends science currently faces in thinking about matter, time, life, and the mind. 

Scientific knowledge isn’t a window onto a disembodied, God’s-eye perspective . It doesn’t grant us access to a perfectly knowable, timeless objective reality, a “view from nowhere,” in philosopher Thomas Nagel’s well-known phrase. Instead, all science is always our science, profoundly and irreducibly human, an expression of how we experience and interact with the world. But our science is also always the world’s science, an expression of how the world interacts with us. Science strives to be a self-correcting narrative. A successful scientific narrative is made from the world and our experience of it evolving together.

What is generative AI?

In the months and years since ChatGPT burst on the scene in November 2022, generative AI (gen AI) has come a long way. Every month sees the launch of new tools, rules, or iterative technological advancements. While many have reacted to ChatGPT (and AI and machine learning more broadly) with fear, machine learning clearly has the potential for good. In the years since its wide deployment, machine learning has demonstrated impact in a number of industries, accomplishing things like medical imaging analysis  and high-resolution weather forecasts. A 2022 McKinsey survey shows that AI adoption has more than doubled  over the past five years, and investment in AI is increasing apace. It’s clear that generative AI tools like ChatGPT (the GPT stands for generative pretrained transformer) and image generator DALL-E (its name a mashup of the surrealist artist Salvador Dalí and the lovable Pixar robot WALL-E) have the potential to change how a range of jobs are performed. The full scope of that impact, though, is still unknown—as are the risks.

Get to know and directly engage with McKinsey's senior experts on generative AI

Aamer Baig is a senior partner in McKinsey’s Chicago office;  Lareina Yee  is a senior partner in the Bay Area office; and senior partners  Alex Singla  and Alexander Sukharevsky , global leaders of QuantumBlack, AI by McKinsey, are based in the Chicago and London offices, respectively.

Still, organizations of all stripes have raced to incorporate gen AI tools into their business models, looking to capture a piece of a sizable prize. McKinsey research indicates that gen AI applications stand to add up to $4.4 trillion  to the global economy—annually. Indeed, it seems possible that within the next three years, anything in the technology, media, and telecommunications space not connected to AI will be considered obsolete or ineffective .

But before all that value can be raked in, we need to get a few things straight: What is gen AI, how was it developed, and what does it mean for people and organizations? Read on to get the download.

To stay up to date on this critical topic, sign up for email alerts on “artificial intelligence” here .

Learn more about QuantumBlack , AI by McKinsey.

What every CEO should know about generative AI

What’s the difference between machine learning and artificial intelligence, about quantumblack, ai by mckinsey.

QuantumBlack, McKinsey’s AI arm, helps companies transform using the power of technology, technical expertise, and industry experts. With thousands of practitioners at QuantumBlack (data engineers, data scientists, product managers, designers, and software engineers) and McKinsey (industry and domain experts), we are working to solve the world’s most important AI challenges. QuantumBlack Labs is our center of technology development and client innovation, which has been driving cutting-edge advancements and developments in AI through locations across the globe.

Artificial intelligence is pretty much just what it sounds like—the practice of getting machines to mimic human intelligence to perform tasks. You’ve probably interacted with AI even if you don’t realize it—voice assistants like Siri and Alexa are founded on AI technology, as are customer service chatbots that pop up to help you navigate websites.

Machine learning is a type of artificial intelligence. Through machine learning, practitioners develop artificial intelligence through models that can “learn” from data patterns without human direction. The unmanageably huge volume and complexity of data (unmanageable by humans, anyway) that is now being generated has increased machine learning’s potential , as well as the need for it.

What are the main types of machine learning models?

Machine learning is founded on a number of building blocks, starting with classical statistical techniques  developed between the 18th and 20th centuries for small data sets. In the 1930s and 1940s, the pioneers of computing—including theoretical mathematician Alan Turing—began working on the basic techniques for machine learning. But these techniques were limited to laboratories until the late 1970s, when scientists first developed computers powerful enough to mount them.

Until recently, machine learning was largely limited to predictive models, used to observe and classify patterns in content. For example, a classic machine learning problem is to start with an image or several images of, say, adorable cats. The program would then identify patterns among the images, and then scrutinize random images for ones that would match the adorable cat pattern. Generative AI was a breakthrough. Rather than simply perceive and classify a photo of a cat, machine learning is now able to create an image or text description of a cat on demand.

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How do text-based machine learning models work how are they trained.

ChatGPT may be getting all the headlines now, but it’s not the first text-based machine learning model to make a splash. OpenAI’s GPT-3 and Google’s BERT both launched in recent years to some fanfare. But before ChatGPT, which by most accounts works pretty well most of the time (though it’s still being evaluated), AI chatbots didn’t always get the best reviews. GPT-3 is “by turns super impressive and super disappointing,” said New York Times tech reporter Cade Metz in a video where he and food writer Priya Krishna asked GPT-3 to write recipes for a (rather disastrous) Thanksgiving dinner .

The first machine learning models to work with text were trained by humans to classify various inputs according to labels set by researchers. One example would be a model trained to label social media  posts as either positive or negative. This type of training is known as supervised learning because a human is in charge of “teaching” the model what to do.

The next generation of text-based machine learning models rely on what’s known as self-supervised learning. This type of training involves feeding a model a massive amount of text so it becomes able to generate predictions. For example, some models can predict, based on a few words, how a sentence will end. With the right amount of sample text—say, a broad swath of the internet—these text models become quite accurate. We’re seeing just how accurate with the success of tools like ChatGPT.

What does it take to build a generative AI model?

Building a generative AI model has for the most part been a major undertaking, to the extent that only a few well-resourced tech heavyweights have made an attempt . OpenAI, the company behind ChatGPT, former GPT models, and DALL-E, has billions in funding from bold-face-name donors. DeepMind is a subsidiary of Alphabet, the parent company of Google, and even Meta has dipped a toe into the generative AI model pool with its Make-A-Video product. These companies employ some of the world’s best computer scientists and engineers.

But it’s not just talent. When you’re asking a model to train using nearly the entire internet, it’s going to cost you. OpenAI hasn’t released exact costs, but estimates indicate that GPT-3 was trained on around 45 terabytes of text data—that’s about one million feet of bookshelf space, or a quarter of the entire Library of Congress—at an estimated cost of several million dollars. These aren’t resources your garden-variety start-up can access.

What kinds of output can a generative AI model produce?

As you may have noticed above, outputs from generative AI models can be indistinguishable from human-generated content, or they can seem a little uncanny. The results depend on the quality of the model—as we’ve seen, ChatGPT’s outputs so far appear superior to those of its predecessors—and the match between the model and the use case, or input.

ChatGPT can produce what one commentator called a “ solid A- ” essay comparing theories of nationalism from Benedict Anderson and Ernest Gellner—in ten seconds. It also produced an already famous passage describing how to remove a peanut butter sandwich from a VCR in the style of the King James Bible. Image-generating AI models like DALL-E 2 can create strange, beautiful images on demand, like a Raphael painting of a Madonna and child, eating pizza . Other generative AI models can produce code, video, audio, or business simulations .

But the outputs aren’t always accurate—or appropriate. When Priya Krishna asked DALL-E 2 to come up with an image for Thanksgiving dinner, it produced a scene where the turkey was garnished with whole limes, set next to a bowl of what appeared to be guacamole. For its part, ChatGPT seems to have trouble counting, or solving basic algebra problems—or, indeed, overcoming the sexist and racist bias that lurks in the undercurrents of the internet and society more broadly.

Generative AI outputs are carefully calibrated combinations of the data used to train the algorithms. Because the amount of data used to train these algorithms is so incredibly massive—as noted, GPT-3 was trained on 45 terabytes of text data—the models can appear to be “creative” when producing outputs. What’s more, the models usually have random elements, which means they can produce a variety of outputs from one input request—making them seem even more lifelike.

What kinds of problems can a generative AI model solve?

The opportunity for businesses is clear. Generative AI tools can produce a wide variety of credible writing in seconds, then respond to criticism to make the writing more fit for purpose. This has implications for a wide variety of industries, from IT and software organizations that can benefit from the instantaneous, largely correct code generated by AI models to organizations in need of marketing copy. In short, any organization that needs to produce clear written materials potentially stands to benefit. Organizations can also use generative AI to create more technical materials, such as higher-resolution versions of medical images. And with the time and resources saved here, organizations can pursue new business opportunities and the chance to create more value.

We’ve seen that developing a generative AI model is so resource intensive that it is out of the question for all but the biggest and best-resourced companies. Companies looking to put generative AI to work have the option to either use generative AI out of the box or fine-tune them to perform a specific task. If you need to prepare slides according to a specific style, for example, you could ask the model to “learn” how headlines are normally written based on the data in the slides, then feed it slide data and ask it to write appropriate headlines.

What are the limitations of AI models? How can these potentially be overcome?

Because they are so new, we have yet to see the long tail effect of generative AI models. This means there are some inherent risks  involved in using them—some known and some unknown.

The outputs generative AI models produce may often sound extremely convincing. This is by design. But sometimes the information they generate is just plain wrong. Worse, sometimes it’s biased (because it’s built on the gender, racial, and myriad other biases of the internet and society more generally) and can be manipulated to enable unethical or criminal activity. For example, ChatGPT won’t give you instructions on how to hotwire a car, but if you say you need to hotwire a car to save a baby, the algorithm is happy to comply. Organizations that rely on generative AI models should reckon with reputational and legal risks involved in unintentionally publishing biased, offensive, or copyrighted content.

These risks can be mitigated, however, in a few ways. For one, it’s crucial to carefully select the initial data used to train these models to avoid including toxic or biased content. Next, rather than employing an off-the-shelf generative AI model, organizations could consider using smaller, specialized models. Organizations with more resources could also customize a general model based on their own data to fit their needs and minimize biases. Organizations should also keep a human in the loop (that is, to make sure a real human checks the output of a generative AI model before it is published or used) and avoid using generative AI models for critical decisions, such as those involving significant resources or human welfare.

It can’t be emphasized enough that this is a new field. The landscape of risks and opportunities  is likely to change rapidly in coming weeks, months, and years. New use cases are being tested monthly, and new models are likely to be developed in the coming years. As generative AI becomes increasingly, and seamlessly, incorporated into business, society, and our personal lives, we can also expect a new regulatory climate  to take shape. As organizations begin experimenting—and creating value—with these tools, leaders will do well to keep a finger on the pulse of regulation and risk.

Articles referenced include:

• " Implementing generative AI with speed and safety ,” March 13, 2024, Oliver Bevan, Michael Chui , Ida Kristensen , Brittany Presten, and Lareina Yee
• “ Beyond the hype: Capturing the potential of AI and gen AI in tech, media, and telecom ,” February 22, 2024, Venkat Atluri , Peter Dahlström , Brendan Gaffey , Víctor García de la Torre, Noshir Kaka , Tomás Lajous , Alex Singla , Alex Sukharevsky , Andrea Travasoni , and Benjamim Vieira
• “ As gen AI advances, regulators—and risk functions—rush to keep pace ,” December 21, 2023, Andreas Kremer, Angela Luget, Daniel Mikkelsen , Henning Soller , Malin Strandell-Jansson, and Sheila Zingg
• “ The economic potential of generative AI: The next productivity frontier ,” June 14, 2023, Michael Chui , Eric Hazan , Roger Roberts , Alex Singla , Kate Smaje , Alex Sukharevsky , Lareina Yee , and Rodney Zemmel
• “ What every CEO should know about generative AI ,” May 12, 2023, Michael Chui , Roger Roberts , Tanya Rodchenko, Alex Singla , Alex Sukharevsky , Lareina Yee , and Delphine Zurkiya
• “ Exploring opportunities in the generative AI value chain ,” April 26, 2023, Tobias Härlin, Gardar Björnsson Rova , Alex Singla , Oleg Sokolov, and Alex Sukharevsky
• “ The state of AI in 2022—and a half decade in review ,” December 6, 2022,  Michael Chui ,  Bryce Hall ,  Helen Mayhew , Alex Singla , and Alex Sukharevsky
• “ McKinsey Technology Trends Outlook 2023 ,” July 20, 2023,  Michael Chui , Mena Issler,  Roger Roberts , and  Lareina Yee  
• “ An executive’s guide to AI ,” Michael Chui , Vishnu Kamalnath, and Brian McCarthy
• “ What AI can and can’t do (yet) for your business ,” January 11, 2018,  Michael Chui , James Manyika , and Mehdi Miremadi

This article was updated in April 2024; it was originally published in January 2023.

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