What makes someone the same person after a period of time in which they have changed, both bodily and psychologically? In answering this question, Locke involves himself in asking three questions. What constitutes sameness of substance? What makes someone at a later date the same man? And finally, what makes someone at a later date the same person?
It would be reasonable to argue that we were dealing with the same substance if none of the particles, of which an object is composed, have changed. Obviously, with a living organism this never occurs since parts are continually being lost or renewed. So sameness of physical substance won’t be a useful criterion for determining personal identity over time since no living human being ever maintains precisely the same physical constituents from moment to moment.
For Locke, a “man” is a particular biological organism: a member of the species Homo Sapiens. A man is like an oak tree in this respect. A huge spreading oak tree is still the same oak it was twenty years ago, despite having doubled in size and shed its leaves twenty times. It is not the same substance, but it is the same oak, in virtue of the continued function of its living parts. In the same way, I am the same person I was three years ago, despite both physical and psychological changes which anyone should be able to notice.
According to Locke, a person is “a thinking intelligent Being, that has reason and reflection, and can consider it self as it self, the same thinking thing in different times and places” (book2 ch27 §9). One might also want to include that persons are necessarily subjects of perception and authors of intentional action i.e. they’re both percipients and agents. In other words, a person isn’t simply a member of our species since some human beings lack the power of reason and self-consciousness.
According to Locke, the criterion of personal identity over time is not simply bodily continuity, since that does not guarantee us that we are dealing with the same person. Rather, personal identity stretches only so far as consciousness will stretch: as far as this consciousness can be extended backwards to any past action or thought, so far reaches the identity of that person? (book2 ch27 §9). No matter how much I’ve changed physically, if I can remember my past actions as my own, then I am the same person that I was.
Locke emphasizes this idea with a thought experiment. Imagine that one day a prince wakes up to find that he has all the memories of a cobbler, and none of his own. His body remains unchanged. On the same morning a cobbler wakes up to find that he has all the prince’s memories. Locke maintains that, although the prince-bodied individual remains the same man, he is not the same person that he was when he went to sleep. It would not be fair to hold the prince-bodied person responsible for the prince’s former actions, since he would not have any recollection of having performed them. This example is proposed to bring out the important difference between the terms “man” and “person”.
It would seem that on Locke’s account we should never punish people for what they can’t remember doing since they would not be the same persons who committed the acts. “Person” for Locke is a term which is particularly relevant to legal questions which relate to the responsibility of one’s actions. It would seem then that we should never punish a murderer who can’t remember killing. Locke’s view on this is that in cases of memory loss or alleged memory loss, we tend to assume that if we have identified the man who performed the actions, then this must be the same person who committed them. We punish drunks for their actions even if they claim not to be able to remember what they did. However, this is simply a result of the difficulty of anyone proving their ignorance of what they did. The law has to be practical and so rarely accepts memory loss as an excuse.
The philosopher Thomas Reid countered Locke’s claim that memory provides an adequate criterion of personal identity with the following example. Imagine a brave officer who was once flogged at school for stealing from an orchard. In his first campaign as a young soldier he succeeded in capturing a fort from the enemy. When he captured the fort he could remember that he has been flogged as a boy. Later, he was made a general. By that time, he could remember capturing the fort, but he could no longer remember being flogged at school. The person who captured the fort is, on Locke’s account, the same person who was flogged, because of the memory link. Similarly, the memory link makes the general the same person as the young officer who captured the fort, but the general is not the same person as the boy. However, the principle of transitivity tells us that if the boy is the same person as the young officer, and the officer the same person as the general, then the boy must be the same person as the general. If X is the same as Y, and Y is the same as Z, then X is the same as Z. Reid’s point is that Locke’s account gives us two contradictory conclusions: both that the boy and the general are the same person, and that they are not. Any theory which leads to such an obvious contradiction must be false.
Locke’s response to this sort of criticism would have to be that the boy and the general are the same man but not the same person, and that it would be wrong to hold the general responsible for what the boy did. Locke could try to deny the principle of transitivity, but this seems exceptionally difficult.
Another criticism comes from the philosopher Joseph Butler. His argument was that consciousness of personal identity presupposes, and therefore cannot compose, personal identity. On Locke’s account, we can infer from the fact that I remember doing X that I was the person that did X. According to Butler, this must be false because the formulation of my memory claim already has built in to it the fact that I was the person concerned. We tend to say “I remember doing X”, but this is just an abbreviated version of “I remember that I was the person that was doing X”? His proposition is that the memory claim contains within it an assertion of identity, and therefore it cannot be regarded as an independent premise from which identity can be inferred. Consequently memory cannot be the only criterion for personal identity.
What these criticisms of Locke’s theory of personal identity show; is that we would have to refine his thoughts to get a better idea of exactly what constitutes “sameness”. However, this process might leads us so far away from Locke’s account as to leave them incomparable.
Written back in the good ole days of 2004.