Hume begins his discussion of personal identity by, strikingly, denying that we have any idea of the self:
“There are some philosophers, who imagine we are every moment conscious of what we cal our SELF; that we feel its existence and continuance in existence; and are certain, beyond the evidence of a demonstration, both of its perfect identity and simplicity. ...[But] from what impression could this idea be deriv’d? ...For my part, when I enter most intimately into what I call myself, I always stumble on some particular perception or 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 anything but the perception.
...I may venture to affirm ...that [persons] are nothing but a bundle or collection of different perceptions, which succeed each other with an inconceivable rapidity, and are in perpetual flux and movement.”
It is, at first, hard to see how this could fit into a discussion of personal identity. If Hume’s idea is that we never notice any self beyond particular mental events, isn’t he denying that there is such a thing as personal identity, rather than giving an account of it? To answer this question, we’ll have to look at Hume’s ideas on change and identity in general, a topic to which he turns next.
Hume thinks that we confuse the ideas of identity and diversity (or, as we might put it, distinctness). Examples of identity and diversity are easy to give:
“We have a distinct idea of an object, that remains invariable and and uninterrupted thro’ a suppos’d variation of time; and this idea we call that of identity ...we have also a distinct idea of several objects existing in succession, and connected together by a close relation; and this to an accurate view affords ...a notion of diversity ...”
But things are less clear when we consider the case of (what we would call) one object changing over time. Here’s what Hume says about this case:
“suppose any mass of matter to be plac’d before us ...supposing some small or inconsiderable part to be added to the mass, or subtracted from it; tho’ this absolutely destroys the identity of the whole, strictly speaking; yet as we seldom think so accurately, we scruple not to pronounce a mass of matter the same, where we find so trivial an alteration ...and are apt to imagine that ’tis nothing but a continu’d survey of the same object.
...A change in any considerable part of a body destroys its identity; but ’tis remarkable, that where the change is produced gradually and insensibly we are less apt to ascribe to it the same effect. The reason can plainly be no other, than that the mind, in following the successive changes of the body, feels an easy passage from the surveying its condition in one moment to the viewing of it in another ...”
Hume’s line of thought here seems to be something like this: if we change some object x sufficiently, we say that we now have a new object, y, which is not identical to x. But if we change it gradually, or slightly, we are inclined to say that the object before us now is identical to the original object, x. But it is hard to see why it should matter whether an object changes gradually, or dramatically — especially when we consider (256) that we don’t seem to have a fixed standard for distinguishing gradual from dramatic changes. So the most plausible view seems to be that even in cases of gradual change, we have a change in the identity of the object. In such cases, our inclination to regard the object as the same is simply a mistake: the mistake of confusing qualitative (or, as Hume says, ‘specific’) and numerical identity:
“tho’ we commonly be able to distinguish pretty exactly betwixt numerical and specific identity, yet it sometimes happens, that we confound them, and in our thinking and reasoning employ the one for the other.”
Hume seems to think that whenever an object changes and we say that the object after the change is identical to the object before the change, we are confusing numerical and qualitative identity. (What should Hume say about cases in which an object does not change from one time to another? Is it still numerically the same object?)
Moreover, this mistake is accompanied characteristically by another:
“the controversy concerning identity is not merely a dispute of words. For when we attribute identity, in an improper sense, to variable or interrupted objects, our mistake is not confin’d to the expression, but is commonly attended with a fiction, either of something invariable and uninterrupted, or of something mysterious and inexplicable ...”
So, not only do we confuse numerical and qualitative identity in cases of change, but, to support our mistaken opinion that the changed object before us is numerically identical to something before the change, we invent some aspect of the object which has remained unchanged throughout.
Hume thought that this tendency goes a long way towards explaining mistaken views about personal identity. For, he thought, when we encounter several different things existing in succession and differing gradually, one from the next,
“This resemblance is the cause of the confusion and mistake, and makes us substitute the notion of identity, instead of that of related objects. ...Our propensity to this mistake is so great ...that we fall into it before we are aware; and tho’ we incessantly correct ourselves by reflexion, and return to a more accurate method of thinking, yet we cannot long sustain our philosophy ...Our last resource is to yield to it, and boldly assert that these different related objects are in effect the same, however interrupted and variable. In order to justify to ourselves this absurdity, we often feign some new and unintelligible principle, that connects the objects together, and prevents their interruption or variation. Thus we feign the continu’d existence of the perceptions of our senses ...and run into the notion of a soul, and self, and substance, to disguise the variation.”
But we should resist this mistake, and think of persons over time in the same way that Hume encourages us to think of other changing objects:
“And here [in the case of personal identity] ’tis evident, the same method of reasoning must be continu’d ...The identity, which we ascribe to the mind of man, is only a fictitious one, and of a like kind with that which we ascribe to vegetables and animal bodies. It cannot, therefore, have a different origin, but must proceed from a like operation of the imagination upon like objects.” (259)
So, as in the case of other objects, we should think of (what we call) persons changing over time as a succession of closely related but numerically distinct objects.
The relations which Hume though relevant here were causation and resemblance (260-1). About the former he says:
“we may observe, that the true idea of the human mind, is to consider it as a system of different perceptions or different existences, which are link’d together by the relation of cause and effect, and mutually produce, destroy, influence, and modify each other. Our impressions give rise to their correspondent ideas; and these ideas in their turn produce other impressions. ...as the same individual republic may not only change its members, but also its laws and constitutions; in like manner the same person may vary his character and disposition, as well as his impressions and ideas, without losing his identity. Whatever changes he endures, his several parts are still connected by the relation of causation.”
So a person, in Hume’s view, is something like a chain of mental events, related to each other as cause and effect.
This is like Locke’s theory in that it explains sameness of persons over time in terms, broadly, of psychological characteristics and relations rather than material identity or persistence of an immaterial soul. But it differs from it in at least two respects.
The first should be obvious from the above: Locke does not seem to think that there is any particular problem with objects being genuinely numerically identical through change. So he would not seem to share Hume’s view that there is a sense in which thinking of personal identity as genuinely identity is a mistake.
The second concerns the role of memory. Recall that Locke thought that
“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.” (§10)
So Locke seems to think that personal identity is to be analyzed partly in terms of memory, or repeating of ideas. But Hume thinks that this gets things backwards. Personal identity is to be explained in terms of causal relations between mental events, and these causal relations are what make memory possible:
“Had we no memory, we never should 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 ...For how few of our past actions are there, of which we have any memory? ...Or will he affirm, because he has entirely forgot the incidents of these days, that the present self is not the same person with the self of that time; and by that means overturn all the most establish’d notion so of personal identity? In this view, therefore, memory does not so much produce as discover personal identity, by shewing us the relation of cause and effect among our different perceptions.”
What is Hume’s argument here? How should Locke respond?
Hume’s discussion of personal identity concludes with a striking claim:
“The whole of this doctrine leads us to a conclusion, which is of great importance in the present affair ...that all the nice and subtile questions concerning personal identity can never possibly be decided, and are to be regarded rather as grammatical than as philosophical difficulties. Identity depends upon the relations of ideas ...But as the relations ...may diminish by insensible degrees, we have no just standard, by which we can decide any dispute concerning the time, when they acquire or lose a title to the name of identity. All the disputes concerning the identity of connected objects are merely verbal ...”
Why does Hume say this? What does the fact that the relations of cause and effect can ‘diminish by insensible degrees’ have to do with his conclusion?