The second proposal about personal identity says that personal identity is just a matter of having the same body:
Proposal #2: A is the same person as B iff A and B have the same body.
A variant of proposal #2 would say instead:
Proposal #3: A is the same person as B iff A and B have the same brain.
But we won’t discuss this view until a few classes later.
Sam Miller objects to Proposal #2 with an argument much like the arguments Gretchen used against Proposal #1. He argues that, if Proposal #2 were correct, then it would be much more difficult to have knowledge or reasonable beliefs about personal identity than we ordinarily take it to be. One assumption that we ordinarily make is that one can have reasonable beliefs about one’s own identity over time, without having to check and see if one has the same body as one did formerly. But if Proposal #2 were correct, then it’s hard to see how we’d be entitled to that assumption (see pp. 19-21).
Sam also objects to Proposal #2 on the grounds that it seems possible for a person to wake up in a new body than he or she formerly occupied. Certainly we can imagine this happening. We can even imagine it happening to ourselves! But according to Proposal #2, this would not in fact be possible (pp. 21-22).
We have to be careful with criticisms like this second one. As you’ll see if you read more about philosophy of mind or philosophy of language, the mere fact that we can imagine some event is nowadays not widely agreed to show that the event is genuinely possible. For example, a materialist will grant to Descartes and other dualists that we can imagine existing without any body, but the materialist denies that this is genuinely possible. Similarly, the proponent of Proposal #2 might accept that we can imagine coming to occupy a new body. He just denies that this is genuinely possible.
But if you think that it is genuinely possible (even in principle) to come to occupy a new body, then you should reject Proposal #2.
The next proposal about personal identity takes a bit more time to introduce.
Suppose you’re at a baseball game. It’s a double-header. Near the end of the first game, you step out for some food. When you come back, you see that it’s a different inning than when you left. But you’re not sure whether this is still the first game, or whether the second game has started already. That is, you’re not sure whether the inning you saw when you stepped out is part of the same game as the inning you see now.
This raises a question: what is it about the innings, and their relations to each other, that would make them parts of a single game, rather than parts of two different games?
Think about how we should answer that question. That is, try to come up with a theory that tells us when two innings count as parts of a single baseball game. (Some ideas to get you started: The innings have to involve the same teams. They have to take place on the same field. The score in the later inning cannot be lower than the score in the earlier inning.)
We can think of a train as consisting of a lot of boxcars connected to each other in certain ways. Similarly, we can think of a baseball game as consisting of a lot of innings connected to each other in certain ways. The boxcars are spatial segments of the train; whereas the innings are temporal segments of the baseball game. (Sometimes they’re called time-slices of the baseball game.) Despite these differences, though, there are certain analogies between the two cases. In both cases, we can tell a story about how the segments have to be connected to each other, in order to make up a single train or game.
Let’s try thinking of persons in this way. Imagine a person divided up into a number of different time-slices, or person stages. Can we tell a story about how those time-slices have to be connected to each other, in order to make up a single person? If we could do that, then we’d be able to answer puzzling questions about personal identity. Instead of asking whether A and B are one and the same person, we could instead ask whether a certain person stage A* and another person stage B* are parts of a single person.
Now, our next proposal about personal identity tells us that the way person stages have to be connected, in order to make up a single person, is by memory. The later stages in a person’s life have to remember events experienced by the earlier stages. As a first stab, we can formulate this as follows:
Proposal #4 (first stab): Stage A* and stage B* are parts of the same person iff the later stage remembers events experienced by the earlier stage (p. 26).
However, for a number of reasons, this formulation is too crude. Let’s try fixing it up.
First, we shouldn’t require that the memories have to actually be played back right at that moment. It should be enough that the later stage is able to remember the events.
For another thing, we want to make sure we’re talking about genuine memories, not mere apparent memories. The mere fact that I seem to remember events in Napoleon’s life does not make me the same person as Napoleon.
Third, we want to make sure that we’re talking about events remembered “from the inside.” I remember my sister getting ready for her high school prom, and that’s an event which my sister experienced. But that doesn’t make me the same person as my sister. I remember that event “from the outside,” whereas she remembers it “from the inside.” It’s only the latter sorts of memories that should count when we’re making judgments about personal identity.
Fourth, it’s too strict to require that later stages in a person’s life remember some event experienced by each earlier stage in that person’s life. People can forget things, while still remaining the same person. So A* might be an early part of the same person as B*, even though B* cannot remember any of the events experienced by A*.
What we should require, instead, is that there be a list of person-stages, where the later stage at each link remembers events experienced by the immediately preceding stage. So long as A* and B* are connected by such a chain, it is not necessary that B* remembers any of the events that A* himself experienced.
Putting all of these together, we get a fixed-up version of Proposal #4:
Proposal #4 (fixed-up version): Stage A* and stage B* are parts of the same person iff they are parts of a list or chain, all of whose later stages genuinely remember (or are able to remember) “from the inside” (enough details of some) events experienced by the immediately preceding stages.
Next time we’ll discuss a serious objection to this proposal, and how we might respond to it…