Locke famously maintained that personal identity is not the same thing as the identity of a human animal (a “man” in Locke’s terminology). He argued for this conclusion with the example of the Prince and the Cobbler. Imagine that the person who wakes up in the Cobbler’s bed, in what was the Cobbler’s body, has all the knowledge, memories, character traits, and thoughts that only the Prince can have. Wouldn’t we say that this person is the Prince? And if we say that, then having the same living body as the Cobbler is not a sufficient condition of being the Cobbler.
And if we imagine the Cobbler switching into what was the Prince’s body, we will see that having the same living body is not a necessary condition of being the same person either. If that could happen, then the Cobbler person can continue to exist from last night through this morning despite not having the same living body. He went to bed last night in his own house and his own body but woke up in the Prince’s bed and body while remaining the same person throughout.
Williams questions this so-called “body-switching” example. Specifically, he describes it twice. One description is the one that is familiar enough from Locke and the movies: two people seem to switch bodies. The other description is exactly the same, only it leaves out the second person. When described in this way, we are strongly inclined to say that the person stays with the body. All that happens is that the person starts believing that he or she is someone else.
But, Williams asks, why should it matter whether there is a second person involved? He thinks that whether someone else is run through the experiment along with me can’t determine whether I survive the experiment or not.
One person can change in many ways while still remaining the same person. I don’t die when I get a haircut, despite the fact that this makes me physically different. By the same token, I can survive lots of psychological changes. I can learn new things, forget old ones, change character, and so on. I may become qualitatively different over time while remaining numerically the same person.
The core of Williams’s argument is a spectrum of cases. At one end are changes that most of us think a person can undergo while remaining the same. I can suffer amnesia while remaining the same person, for instance. At the other end is the apparent body switch: my body gets an entirely new set of memories and character traits derived from someone else’s mind while their body gets memories and character traits derived from my mind.
Williams tries to show that these reactions are inconsistent. If I think I can survive amnesia in my old body, then I should also think that I would stay in my old body even after my memories and character traits are copied into a different body.
The challenge for those who disagree with him is to draw a line between one kind of case and the others, such that on one side of the line, you stay with your body while on the other you leave your body, either by dying or by switching to a different body.
Alex pointed out that Williams’s argument relies on an answer to a question: would you fear torture after undergoing the changes in any particular step on the spectrum. So, for instance, he asks whether you would fear torture after having induced amnesia. If the answer is “yes,” that shows you anticipate feeling the torture and that, in turn, shows that you don’t think that having memories of your thoughts and experiences is essential to being the same person as you.
Alex, though, found this suspect. Fear isn’t a reliable indicator of the truth: we fear lots of stuff that isn’t real and we tend to fear the unknown, especially if torture is involved. So the reactions Williams gets to his imagined experiments may be much less revealing than he thinks.
I think that’s a good point. Fear isn’t wholly irrational, though. If you fear ghosts, and then become convinced that there are no such things as ghosts, you will, typically, lose your fear of ghosts. The question is whether it makes sense to anticipate torture in these cases or whether they are more akin to having a residual fear of ghosts despite firmly believing there are no such things.