Hume's Theory of Mind

David Hume (1711-1776) is often considered the last of the trio of great British philosophers consisting of himself, Locke, and Berkeley. Hume’s major philosophical works — A Treatise of Human Nature (1739-1740), the Enquiry concerning Human Understanding (1748) and Enquiry concerning the Principles of Morals (1751), as well as the posthumously published Dialogues concerning Natural Religion (1779) — were scandalous in their time and remain widely and deeply influential in contemporary analytic philosophy. Hume’s first major work, the Treatise on Human Nature, published when he was only 28, was however wildly unpopular. It sold very few copies, and Hume jested that it fell “dead-born from the press.” Hume aspired to, but never received, an academic post. He was turned down at both Edinburgh and Glasgow.

Though Hume’s interests, philosophical and otherwise, ranged widely (for example, he wrote the important History of England, in six volumes), he is perhaps best known for his model of the human mind, his critiques of causality, necessity, and induction, his views on personal identity, and his scathing attacks on organized religion. In this current set of notes we focus on his views of the mind. It was this set of views which led most clearly to his rather devastating assessment of the study of metaphysics, surely one of the most famous pronouncements in the history of philosophy, from his Enquiry.

When we run over libraries, persuaded of these principles [i.e. Hume’s principles of experience], what havoc must we make? If we take in our hand any volume; of divinity or school metaphysics, for instance; let us ask, Does it contain any abstract reasoning concerning quantity or number? No. Does it contain any experimental reasoning concerning matter of fact and existence? No. Commit it then to the flames: For it can contain nothing but sophistry and illusion. (EHU §12.34,

The Aim of the Enquiry

Hume sets out in the Enquiry to achieve two broad aims, one negative and the other positive. His negative aim is to demonstrate the fruitlessness of pursuing metaphysical questions. Such ‘abstruse questions’ 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 brambles to cover and protect their weakness. (EHU §1.11, p. 8)

In either case, according to Hume, metaphysics isn’t scientific (in the Aristotelian sense of being an organized and self-standing body of knowledge) and never will be.

Hume believes that the negative aim of demonstrating the folly of metaphysical pursuits is demonstrated via the accomplishment of his positive aim, which he says is to,

enquire seriously into the nature of 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. (EHU §1.12, p. 9)

In some ways then, Hume’s Enquiry has much the same aim as Locke’s Essay. Both want to articulate the nature and limits of human knowledge by means of an investigation of the faculties by which such knowledge is acquired, and in doing so settle longstanding philosophical disputes. Also, like Locke, Hume will arrive at a conception of the human mind as far more limited than it had been taken to be by many, particularly those philosophers and theologians who had confidence in the capacity of the human mind to reveal fundamental truths concerning the nature of reality and the existence and nature of God.

Hume’s Theory of Mind

Hume considers his project of articulating the nature of human understanding as akin to Newton’s unification of natural phenomena according to his mechanical laws.

Astronomers had long contented themselves with proving, from the phenomena, the true motions, order, and magnitude of the heavenly bodies: Till a philosopher [Newton], at last, arose, who seems, from the happiest reasoning, to have also determined the laws and forces, by which the revolutions of the planets are governed and directed. The like has been performed with regard to other parts of nature. And there is no reason to despair of equal success in our enquiries concerning the mental powers and economy, if prosecuted with equal capacity and caution. (EHU §1.15, p. 11)

Hence, Hume intends to articulate the basic laws or forces by which the human mind operates, and thus unify the various phenomena that constitute human experience and knowledge under as limited a number of basic elements as possible, and show that the interaction of these elements according to some basic ‘laws’ will provide all we need to explain the nature and extent of human knowledge. Hume thus aims to do for psychology what Newton did for physics.

Impressions & Ideas

Hume’s anatomy of the mind begins with its ‘perceptions’. These are of two basic kinds – impressions and ideas.

we may divide all the perceptions of the mind into two classes or species, which are distinguished by their different degrees of force and vivacity. The less forcible and lively are commonly denominated thoughts or ideas. The other species want a name in our language, and in most others; I suppose, because it was not requisite for any, but philosophical purposes, to rank them under a general term or appellation. Let us, therefore, use a little freedom, and call them impressions; employing that word in a sense somewhat different from the usual. By the term impression, then, I mean all our more lively perceptions, when we hear, or see, or feel, or love, or hate, or desire, or will. And impressions are distinguished from ideas, which are the less lively perceptions, of which we are conscious, when we reflect on any of those sensations or movements above mentioned. (EHU §2.3, p. 15)

Impressions and ideas differ by virtue of differences along two dimensions—their ‘force’ and ‘liveliness’ or ‘vivacity’. It is hard to say exactly how we should construe these two dimensions. Certainly, they need to coherently apply to the deliverances of the five senses—sense impressions—as well as emotions and desires. We might get an idea what Hume is on about with the terms ‘force’ and ‘vivacity’ by thinking of the case with color impression. A color might have a greater or lesser degree of brightness. Construe this as its force. Alternatively, we might vary the degree to which the color is saturated. This is its vivacity. Perhaps something analogous could be said of sound with respect to loudness and pitch.

Ideas are less forceful and vivid copies of impressions. As Hume puts it,

all our ideas or more feeble perceptions are copies of our impressions or more lively ones. (EHU §2.5, p. 16)

This ‘Copy Principle’ strictly limits where our ideas can come from. It says not only that our ideas can come from our impressions, but that they can only come from our impressions, as their copies. Sense experience and introspection provide us with simple impressions from which simple ideas may be copied, but simple ideas come from no other source than as copies of simple impressions. Hume does, however, note one apparent counterexample to the Copy Principle, his ‘missing shade of blue.’

There is, however, one contradictory phenomenon, which may prove that it is not absolutely impossible for ideas to arise, independent of their correspondent impressions…Suppose, therefore, a person to have enjoyed his sight for thirty years, and to have become perfectly acquainted with colours of all kinds except one particular shade of blue, for instance, which it never has been his fortune to meet with. Let all the di¡erent shades of that colour, except that single one, be placed before him, descending gradually from the deepest to the lightest; it is 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 between the contiguous colour than in any other. Now I ask, whether it be possible for him, from his own imagination, to supply this deficiency, and raise up to himself the idea of that particular shade, though it had never been conveyed to him by his senses? I believe there are few but will be of opinion that he can: And this may serve as a proof that the simple ideas are not always, in every instance, derived from the correspondent impressions; though this instance is so singular, that it is scarcely worth our observing, and does not merit that for it alone we should alter our general maxim. (EHU §2.8, pp. 17-18)

Hume thinks that this is a ‘singular’ example, whose existence shouldn’t affect the generality of his Copy Principle. But given the work to which he puts the Copy Principle in his critique of rationalist metaphysics, one might worry that the lacuna he points to here renders his broader critique much more doubtful. For example Hume argues that we can use the Copy Principle to assess the cognitive content of particular concepts in metaphysics.

When we entertain, therefore, any suspicion that a philosophical term is employed without any meaning or idea (as is but 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. (EHU §2.9, p. 18)

Hume’s view here is that words express ideas in the minds of subject speaking or hearing the word. So if we begin to suspect the cognitive content of a particular philosophical term, e.g. ‘substantial form’, Hume thinks we should to look to the idea expressed by it. If we can find no fixed idea, then we have reason to criticize the use of the term. Alternatively, if we do find an idea, then Hume asks us to trace the idea (or its ‘parts’) to their corresponding impressions, which constitute the meaning of the idea. If no such connection between idea and impression may be found, then the idea is a fiction, it does not have a cognitive content. It is, in an important sense, meaningless.

Hume concludes that,

though our thought seems to possess this unbounded liberty, we shall find, upon a nearer examination, that it is really confined within very narrow limits, and that all this creative power of the mind amounts to no more than the faculty of compounding, transposing, augmenting, or diminishing the materials afforded us by the senses and experience. (EHU §2.5, pp. 15-16)

Thus, human thought, and with it knowledge, extends only to the bounds of our simple impressions and what may be combined or recombined from those simple materials.


In addition to the basic elements which populate the mind—its impressions and ideas—Hume thinks there is a binding force that governs their combination. This force is what Hume calls “association”, and he argues that it comes in three basic types: resemblance, contiguity in time and space, and cause and effect (EHU §3). Hume considered his theory of association as one of the central contributions of his philosophical psychology. Association, he argues, is the “glue” holding together the perceptions which constitute the mind. All perceptions are capable of standing in associative relations to other perceptions, and it is the existence of such relations that accounts for much of the ebb and flow of our mental lives, as well as the behavior that results from this.

Association based on resemblance is pretty clear – consider what happens when you look at cloud shapes and they make you think of particular kinds of objects or animals. Association based on contiguity might be illustrated by how certain locations (e.g. your childhood bedroom) evoke memories (e.g. growing up in your parents house).

Finally, one associates impressions or ideas with respect to their causes and effects. Every time you drink a caffeinated beverage you enjoy a particular effect. According to Hume, repeated exposure to events of the type drinking coffee and being (or becoming) alert naturally leads to causal association. The thought of drinking a cup of coffee brings to mind thoughts of the feelings associated with it – i.e. its effects (alertness, jitteryness, etc.).

Hume’s conception of association based on cause and effect is central to his conception of the nature of causal reasoning, which he considers the central tool for human beings in coming to have knowledge of the world.


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