Locke’s position is that the identity of a person over time is independent of the identity of substances, whether material or immaterial. He argued for this position by challenging the alternatives. Specifically, he denied that the necessary and sufficient conditions for personal identity that the alternatives propose are correct.
One of his most compelling points rests on an analogy with plant and animal life. No one thinks that an animal’s identity over time depends on its being made up of the same material or immaterial substance. On the contrary, trees and cats are made up of different matter as their lives go on. So why think that a person’s identity must depend on the identity of an underlying substance, whether material or immaterial?
This, naturally enough, gives rise to a second question: why isn’t personal identity just one case of animal identity? That is, why doesn’t the identity of a person consist in the continued life of a human animal, much like the identity of a cat consists in the continued life of a feline animal? Locke disputed this too. He called a human animal a “man” and insisted that a person is distinct from a man. The identity of a person consists in consciousness, but a human animal is frequently unconscious. And, notoriously, Locke thought that a person could, conceivably, switch from one human body to another.
Locke was willing to grant that psychological activity, that is, our thoughts and experiences, depends on either a material or immaterial substance. You can’t think without a material brain or an immaterial soul. (He didn’t know which; neither do I.)
But he denied that you have to have the same material brain or immaterial soul in order to remain the same person.
The examples we discussed were meant to show this. That is, they were meant to show that it is possible for A to be the same person as B even if A and B have different brains, bodies, or immaterial souls.
Another way to put it is that Locke was willing to concede that a person needs to have some material brain or immaterial soul. He just denied that having the numerically identical material brain or immaterial soul was important. A person could survive with a suitable replacement.
Locke thought that what makes a person who he or she is at any moment in time is consciousness of thoughts and experiences. My thoughts are mine, and not yours, if I am conscious of having them and you are not.
So a person’s identity over time consists in the extension of consciousness over time. Of course, you can’t be directly conscious of a past person’s thoughts and experiences. I can’t have the same feeling now that I did when the soccer ball hit my head when I was eight.** I took the fact that I wasn’t bothering to keep track of the ball as a sign that I wasn’t interested in soccer. But I can remember what it was like to get hit and you cannot. (See §9)
It’s an interesting question what Locke would say about Tatiana and Krista Hogan. They seem to share some thoughts and experiences by virtue of the fact that their brains are connected. Heck, it’s an interesting question what anyone would say about them!
One thing worth noting about their story is that the twins themselves pretty clearly can distinguish between one twin’s thoughts and another’s, even though they have this unusual direct access to one another’s brains.
We went through three alternatives:
Locke thought that the first case was uncontroversial. Why should people be any different than plants and animals (§§3–6, §12)? But once you’ve granted that, it’s hard to say why you shouldn’t say something similar about the other two.
He tried to make the point with examples. These examples were supposed to both refute the alternative and show that Locke’s view was correct. So he asked us to take seriously the story of the “very rational Man” who thought he had Socrates’s soul, that is, he asked us to imagine that the man really did have Socrates’s soul (§14, p. 339). Then he claimed that it’s obvious that the very rational Man could not be the same person as Socrates if he could not remember any of Socrates’s thoughts or experiences. If you accept that claim, it follows that having the same soul as Socrates is not a sufficient condition of being the same person as Socrates.
What about being the same living animal or “man,” to use Locke’s terminology? Is being the same man a necessary and sufficient condition of A’s being the same person as B? The example of the Prince and the Cobbler is supposed to refute those conditions. We are supposed to be persuaded that it is possible for the person of the Prince to start in the Prince’s body and move to the Cobbler’s body while remaining the same Prince person. That shows that having the same body is not a necessary condition of the Prince’s continuing to exist as the same person. It also implies that it is not a sufficient condition. If having the same body were a sufficient condition of being the same person, the person in the Cobbler’s body would always be the Cobbler. But many people are persuaded that the person in the Cobbler’s body changed from the Cobbler person to the Prince person.
Dhruv was not persuaded. We’ll subject these sorts of stories to much greater scrutiny when we discuss our next reading, Bernard Williams’s “The Self and the Future.”