Hume on Personal Identity & Skepticism

Hume on Personal Identity

One of the central claims of Descartes’s philosophy is that we have privileged knowledge of our own existence and nature.

Thus, simply by knowing that I exist and seeing at the same time that absolutely nothing else belongs to my nature or essence except that I am a thinking thing, I can infer correctly that my essence consists solely in the fact that I am a thinking thing. It is true that I may have (or, to anticipate, that I certainly have) a body that is very closely joined to me. But nevertheless, on the one hand I have a clear and distinct idea of myself, in so far as I am simply a thinking, non-extended thing; and on the other hand I have a distinct idea of body, in so far as this is simply an extended, non-thinking thing. And accordingly, it is certain that I am really distinct from my body, and can exist without it. (7:78)

This is also a central claim of Leibniz’s philosophy.

Now, reflection is nothing other than attention to what is within us, and the senses do not give us what we already bring with us. Given this, can anyone deny that there is a great deal innate in our mind, since we are innate to ourselves, so to speak, and since we have within ourselves being, unity, substance, duration, change, action, perception, pleasure, and a thousand other objects of our intellectual ideas? And since these objects are immediate and always present to our understanding (though they may not always be perceived consciously on account of our distractions and our needs), why should it be surprising that we say that these ideas, and everything that depends upon them, are innate in us? (I.Preface.294)

Hume is critical of the position that we have any knowledge of the nature of the self (as a mental substance), or any knowledge derived from our knowledge of the nature of the self (e.g. as a unified substance).

The Genealogical Argument

Hume puts his Copy Principle to work in his criticism of the idea of the self. The Copy Principle says that all ideas are copied from impressions. So for any idea, including the idea self, there must be a corresponding simple or complex impression from which it is copied. Hume then asks, from what impression do we derive our idea of self? In the work he wrote before the Enquiry – the Treatise on Human Nature – Hume puts things this way:

THERE are some philosophers, who imagine we are every moment intimately conscious of what we call our SELF; that we feel its existence and its continuance in existence; and are certain, beyond the evidence of a demonstration, both of its perfect identity and simplicity. The strongest sensation, the most violent passion, say they, instead of distracting us from this view, only fix it the more intensely, and make us consider their influence on self either by their pain or pleasure. To attempt a farther proof of this were to weaken its evidence; since no proof can be deriv’d from any fact, of which we are so intimately conscious; nor is there any thing, of which we can be certain, if we doubt of this. Unluckily all these positive assertions are contrary to that very experience, which is pleaded for them, nor have we any idea of self, after the manner it is here explain’d. For from what impression cou’d this idea be deriv’d ? (THN I.iv.6, p. 251)

Hume goes on to argue that all we have are distinct impressions of particular qualities (e.g. a headache, an ache, a feeling of joy), which can exist by themselves, and which provide no basis for thinking that they belong to one particular self.

what must become of all our particular perceptions upon this hypothesis [that there is no impression of a persisting self]? All these [impressions] are different, and distinguishable, and separable from each other, and may be separately consider’d, and may exist separately, and have no need of any thing to support their existence. After what manner, therefore, do they belong to self; and how are they connected with it? For my part, when I enter most intimately into what I call myself, I always stumble on some particular perception of other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never can observe any thing but the perception. (THN I.iv.6, p. 252)

Hume’s contention here is that (i) all impressions are capable of existing and being thought of separately, which means we do not need to posit some distinct subject that has the impression; and (ii) introspection never yields any impression or corresponding idea of a self or subject, but only other impressions or ideas.

Hume recognizes that his argument only shows that we lack any knowledge of the self insofar as it is to be identified with a particular impression. But what about the total collection of impressions? Might the subject be identified with this collection? This is Hume’s ‘bundle’ theory of the self.

I may venture to affirm of the rest of mankind, that they are nothing but a bundle or collection of different perceptions, which succeed each other with an inconceivable rapidity, and are in a perpetual flux and movement…The mind is a kind of theatre, where several perceptions successively make their appearance; pass, re-pass, glide away, and mingle in an infinite variety of postures and situations. There is properly no simplicity in it at one time, nor identity in different; whatever natural propension we may have to image that simplicity and identity. The comparison of the theatre must not mislead us. They are the successive perceptions only, that constitute the mind ; nor have we the most distant notion of the place, where these scenes are represented, or of the materials, of which it is compos’d. (THN I.iv.6, p. 253)

Thus, according to Hume, when we talk about the ‘self’, the ‘thinking subject’, or the ‘mind’, what we are speaking of is a collection of perceptions, plus (presumably) their associative relations. This view entails three surprising conclusions. First, since the ‘bundle’ is in constant flux, there is no subject that persists from moment to moment. Bundles may resemble or be causally related to one another in various ways. But these facts are not sufficient to constitute a persisting subject. A persisting identical subject is, according to Hume a fiction.

Second, since a bundle is just an aggregate of perceptions, what distinguishes one bundle from another (e.g. my mind from yours) depends entirely on the associative relations that hold between parts of bundle (compare the spatial relations that distinguish one pile of stones from another). Since associative relations are entirely extrinsic to their perceptions (i.e. there is no contradiction involved in a perception’s standing in entirely different associative relations than it currently does), there is nothing significant about the perceptions which are the elements of any single bundle. They could just as easily have been elements of other bundles. As we will see, this point causes significant trouble for Hume, and he ultimately recants his whole positive account.

Third, Hume’s position puts our knowledge of internal substance (i.e. the mind) on par with that of external substance by saying that in both cases, we have no such knowledge.

Philosophers begin to be reconcil’d to the principle, that we have no idea of external substance, distinct from the ideas of particular qualities. This must pave the way for a like principle with regard to the mind, that we have no notion of it, distinct from the particular perceptions. (THN Appendix, p. 635)

In this way Hume takes the arguments which previously the Irish skeptic and idealist George Berkeley had applied to external matter and applies them to the mind as well. It is in this sense that Hume can be seen as the most ‘radical’, but also consistent, of the British empiricists.

Identity and Fiction

If Hume is correct about personal identity then most everything we say and think regarding ourselves and others is false. So why do we believe such falsehoods? How did we get ourselves into such an epistemic muddle?

Hume provides a theory of identity, which I will, following Jonathan Bennett [-@bennett2001b], call his ‘Similarity Theory’, that explains why we tend to make such false judgments.

Hume cashes out the notion of identity over time (or ‘diachronic’ identity) in terms of persistence without alteration.

We have a distinct idea of an object, that remains invariable and uninterrupted thro’ a suppos’d variation of time; and this idea we call that of identity or sameness. We have also a distinct idea of several different objects existing in succession, and connected together by a close relation; and this to an accurate view affords as perfect a notion of diversity, as if there was no manner of relation among the objects. (I.iv.6, p. 253)

This, in itself, is a bit surprising. For many philosophers, diachronic identity is wholly compatible with alteration from one moment to the next. Indeed, it is precisely this assumption that generates an issue concerning how things persist through change. Hume seems to dismiss the possibility of identity through alteration in his definition.

Hume thinks that we confuse this notion of (what I will call) strict identity with similarity.

But tho’ these two ideas of identity, and a succession of related objects be in themselves perfectly distinct, and even contrary, yet ‘tis certain, that in our common way of thinking they are generally confounded with each other (I.iv.6, p. 253)

In other words, Hume thinks we are inclined towards such false beliefs concerning personal identity because we regularly mistake similarity for strict identity. We end up engaging in such fictions as personal identity, however, for reasons that Hume thinks are entirely natural. He lists four such reasons.

  • masses of matter which change a very small proportion of their parts (255-6)
  • gradual change of all the parts of a thing (256)
  • linguistic confusion between numeric and qualitative identity (257-8)
  • attribution of identity to constantly changing entities (e.g rivers) (258)

Hume then goes on to articulate his positive theory in which similarity or resemblance constitutes the basis for our thinking that we have ideas of a persisting and substantial subject. He argues that the mechanism by which we grasp the resemblance between one distinct bundle of perceptions and the next is memory.

what is the memory but a faculty, by which we raise up the images of past perceptions? And as an image necessarily resembles its object, must not the frequent placing of these resembling perceptions in the chain of thought, convey the imagination more easily from one link to another, and make the whole seem like the continuance of one object? In this particular, then, the memory not only discovers the identity, but also contributes to its production, by producing the relation of resemblance among the perceptions. The case is the same whether we consider ourselves or others. (I.iv.6, 260-1)

The capacity for memory is thus a necessary condition of coming to think of ourselves or others as persisting beings. Though there is no strict identity between momentarily existing bundles of perceptions, there is a resemblance of current ideas to past impressions, and the recognition of these resemblance relations via their generation in memory leads, according to Hume, to beliefs regarding the persistence of a single thing—the thinking subject or self—through time.

An obvious problems arises for this account however. What about those times which one does not remember (e.g. perhaps after a heavy night of drinking, or a deep sleep)? We do also tend to judge of ourselves and others that we exist even at times which we no longer remember, such as early childhood. Hume resolves this problem by appealing to causation. The causal connections between perceptions can account for the practice of beliefs concerning a persisting subject. So we might say that though memory originates the erronous belief in the existence of a persisting self, it is the set of causal relations that exist between our perceptions that entrenches this notion, and the judgmental practice that comes with it.

As memory alone acquaints us with the continuance and extent of this succession of perceptions, tis to be consider’d, upon that account chiefly, as the source of personal identity. Had we no memory, we never shou’d have any notion of causation, nor consequently of that chain of causes and effects, which constitute our self or person. But having once acquir’d this notion of causation from the memory, we can extend the same chain of causes, and consequently the identity of our persons beyond our memory, and can comprehend times, and circumstances, and actions, which we have entirely forgot, but suppose in general to have existed. (I.iv.6 p. 261-2)

Hume’s Skeptical Conclusion

In the body of the Treatise Hume proposes a view of the self as a non-persisting ‘bundle’ of perceptions. In the Appendix to Book III of the Treatise Hume recants this view.

In short there are two principles, which I cannot render consistent; nor is it in my power to renounce either of them, viz. that (1) all our distinct perceptions are distinct existences, and (2) that the mind never perceives any real connexion among distinct existences. Did our perceptions either inhere in something simple and individual, or did the mind perceive some real connexion among them, there wou’d be no difficulty in the case. For my part, I must plead the privilege of a sceptic, and confess, that this difficulty is too hard for my understanding. I pretend not, however, to pronounce it absolutely insuperable. Others, perhaps, or myself, upon more mature reflexions, may discover some hypothesis, that will reconcile those contradictions. (THN Appendix, p. 636)

Why the sudden doubt? Hume does not make his underlying worry explicit. But he seems to be concerned with the following issue, which I first mentioned above—viz. what distinguishes a mind as one mind? (cf. @bennett2001b, §309) Even if we accept Hume’s conclusion that there is no persisting subject, and that our beliefs concerning such a subject (whether ourselves or others) are false, we still have lots of facts about ersatz or pseudo-subjects (i.e. distinct but similar bundles whose perceptions are causally linked together) that we must account for. How do we do so? Well, given Hume’s point (1) above, we need some connection. As we’ve seen Hume argue in the Enquiry however, there is no real connection (e.g. a necessary causal connection) between distinct existences of which we we can be aware. So we are left with mere regularity, i.e. ‘causation’ in it’s mere associative sense. But Hume defines such associative causation in terms of the previous and persistent conjunction of perceptions in one mind. So Hume has a viciously circular position. He needs to appeal to causation to account for facts concerning mental unity, and he needs the notion of mental unity to account for causation.


  1. [@cottrell2015]; [@thiel2011] ↩︎

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