Hume on personal identity

Hume rejects the view that human beings are intuitively (that is to say – more strongly and immediately than by demonstration) aware of their own self, and that, moreover, they know this self to be simple and strictly self-identical.  On the contrary, argues Hume, the self or person cannot be one simple idea since one simple idea can only be the copy of one simple impression.  However, it is not one but many impressions that give us the sense of a self:  “If any impression gives rise to the idea of self, that impression must continue invariably the same, thro’ the whole course of our lives; since self is suppos’d to exist after that manner.  But there is no impression constant and invariable.”  Rather, our passions and sensations succeed each other.  So, our concept of a simple self cannot be derived from these.  And yet, argues Hume, our notion of self is inextricably bound up with these passions and perceptions:  “I never can catch myself at any time without a perception, and never can observe any thing but the perception.”  Hume goes so far as to say that when the perceptions are removed by sound sleep, the self ceases to exist, as it must also in death.  The self, says Hume, is nothing but a bundle of different perceptions, succeeding each other with great rapidity.
	On Hume’s view, the human tendency to construct the notion of a simple, self-identical person out of this panoply of perceptions rests on an error.  Whether the imagination is considering a single uninterrupted object, or a series of different but related objects, the feeling is very similar.  Thus, it sometimes confounds the latter for the former.  Just as, in animation, the imagination is led to mistake a series of frames for one continuous movement, the imagination mistakes a rapidfire series of perceptions for a single simple identical self.  Given the inconsistency of this notion of self with the great variety of perceptions that elicit it, we posit an underlying substance or soul to disguise the variation.  
	Hume continues that, since there are only three ways in which we can relate disparate ideas – that is, via contiguity, resemblance and cause and effect – it must be through one or more of these relations that we connect disparate perceptions into the fiction of a single, simple self.  He dismisses contiguity as irrelevant to the question of personal identity, and turns his attention to the remaining two types of relations of ideas.
	Memory, says Hume, is just the “faculty, by which we raise up the images of past perceptions.”  Insofar as an image resembles its object, it is therefore clear that, to the extent that our notion of a self is forged by the faculty of memory, the fiction [of the self] resides in the relation of resemblance.  
	Even more important in the construction of the notion of personal identity, writes Hume, is the relation of causation.  Here Hume likens the soul to a commonwealth.  A commonwealth may see over time a complete change not only in its ruler and subjects, but also in its laws and statutes, without being said to become a different commonwealth.  The reason for this is the relation of cause and effect that holds between the disparate parts of the commonwealth.  The prior king may be regarded as the cause of his son, the next king, and so on.  Likewise, writes Hume, people’s perceptions may change dramatically over time, but if they are connected by a causal chain, then they are regarded as inhering in the same identical person.  Here, again, memory plays a key role in allowing us to recall the chain of causes and effects that combine to form the self.  
	As it is integral for considering the relations of both resemblance and causation, memory is the chief source of personal identity for Hume.  Moreover, once we have acquired the notion of causation from memory, we can extend it beyond those ideas that are grasped by the memory.  Thus, even though there are a great many periods of my life that I can no longer remember, I extrapolate from the memories that I do have in order to support the notion of a single self-identical person existing even at those forgotten times.  “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.”