Body Switching?

Notes for November 14

Main points

We discussed two kinds of criticisms of Locke’s account of personal identity.

  1. Criticisms of his reliance on memory.
  2. Williams’s criticism of the body switching examples, like the prince and the cobbler.


Locke maintained that a person at one time is identical with one in the past if and only if the one person can remember the past person’s thoughts and experiences. That’s what he meant by saying “as far as this consciousness can be extended backwards to any past Action or Thought, so far reaches the Identity of that Person” (§9). It is also a clear implication of his discussion of cases such as that of the “very Rational man” who “wanted not Parts or Learning” and nonetheless thought he had Socrates’s soul (§14) and that of the prince and the cobbler (§15).

But as Daniel, Patrick, and Angela have all noted, there are problems.

If remembering a past person’s thoughts and experiences is a necessary condition of being that person, then there are many days in the past when I did not exist. This is so because I now cannot remember anyone’s thoughts and experiences on many days in the past. So, if Locke is right, I could not have been around on those days.

Locke was willing to accept that conclusion. He argued that it is something we are committed to. Locke thought we all agreed that it would be unjust to punish waking Socrates for what sleeping (sleep walking?) Socrates did. This, Locke reasoned, makes sense only if waking and sleeping Socrates are different people (see §§19–22).

I expressed my disagreement with Locke on this point. I think he has the phenomenon only partly right and that there is a different way of explaining our reluctance to punish people in cases like this.

There is another problem. It is that identity is a transitive relationship while remembering is not transitive. If A = B and B = C, then A = C. But if the General remembers the Officer’s experiences and the Officer remembers the Boy’s experiences, it does not follow that the General remembers the Boy’s experiences.

This strongly suggests that memory cannot do the work that Locke needed it to do.

Still, there are those imaginary cases of princes moving into cobbler’s bodies. Those still seem just as persuasive. To accommodate that, I proposed something that is different than Locke’s theory while retaining the essential spirit of the thing. It is that personal identity over time consists in the continuity of psychological elements like memory, character, habits, skills, and the like. A person, according to Locke, is a mind, a thinking thing. So the continued existence of person over time should be the continued existence of a mind even though the elements of the mind change over time. By analogy, a tree is made up of matter but the tree continues to exist even as the matter changes over time.

In other words, I tried to describe a way of thinking about persons that is broadly consistent with what Locke was saying without relying as heavily on memory as Locke himself did.

Williams’s experiment

The second kind of criticism we discussed came from the Williams article. Williams took aim at the cases suggesting body switching is possible. He thought those stories are persuasive only because they are told in a very particular way. You could tell the same story from a different perspective and reach a completely different result, according to him.

That is what he was trying to do with his description of the experiment with A, B, the reward, and the torture. As Williams sees it, if we tell A that he will have his brain manipulated in various ways and then he will be tortured, that does not diminish A’s anticipation of the pain of torture. It just means that he will be crazy and in pain. But if A is still going to be around to feel the torture, then A will survive the psychological changes in the experiment.

Of course, that leaves out the other guy, B. But, Williams asks, why does the fact that the experimenters are also going to mess with B have any bearing on whether A is going to survive?

Now, only nine of us agreed with Williams about this. Twelve of us (well, eleven or twelve, depending on how you count Cyrus) think that A would die once the changes to A’s character are too extensive. If so, A would not have any reason to anticipate and fear feeling the torture, though A would have plenty of reason to anticipate and fear dying, of course.

So that’s where we are going to pick it up on Tuesday.

Key concepts

  1. Problems with using memory as a necessary or sufficient condition of personal identity.
  2. Williams’s experiment.
This page was written by Michael Green for Problems of Philosophy, Philosophy 1, Fall 2013. It was posted November 15, 2013.
Problems of Philosophy