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 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).
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.
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.
The problem has to do with how we're going to explain the notion of genuinely remembering an event "from the inside."
Memory is a factive notion: you can't remembering doing X unless X is something that in fact happened, and you are the person who did X. If you never pulled the cat's tail, then you can't remember pulling the cat's tail. You can only seem to remember pulling it. It doesn't help if someone else pulled the cat's tail. You can only genuinely remember doing this if you are identical to the person who pulled the cat's tail.
That's the source of the trouble. It looks like the notion of genuinely remembering an event "from the inside" presupposes the notion of personal identity. We can't tell whether your apparent memories of pulling the cat's tail are genuine memories, unless we first know whether or not you are identical to the person who pulled the cat's tail. Hence, Proposal #4 is circular in an objectionable way. It purports to tell us what personal identity consists in, but it does so by using notions like memory that already presuppose the notion of personal identity (pp. 27-30).
Let's try to define a notion which is like memory, but which doesn't presuppose the notion of personal identity.
Suppose I try to remember what my grandfather looked like. A certain memory image comes to my mind. Now this memory image might be distorted: my grandfather may never have looked exactly like the face in my memory image. What if there's some guy, Joe Schmoe, whom I never met, who does look exactly like the face in my memory image? Would my memory image then be a memory of Joe Schmoe? Of course not. I never met Joe Schmoe, so I can't be remembering him. It doesn't matter that I have an apparent memory of someone looking a certain way, and Joe Schmoe in fact did look that way. This is not enough for me to be remembering Joe Schmoe.
Similarly, suppose I once stepped on the Queen's toe, but I didn't notice that I had done this; and no one ever told me that I did it. Some years later, a hypnotist implants an apparent memory in my mind of stepping on the Queen's toe. Here I seem to remember stepping on the Queen's toe, and I in fact did step on the Queen's toe. But would we say that I genuinely remember stepping on the Queen's toe? That doesn't sound right. This is a case where I have an apparent memory of stepping on the Queen's toe, and I in fact did step on the Queen's toe. But that's not enough for me to be remembering stepping on the Queen's toe.
What's missing in this cases? What more is required, for an apparent memory to be a genuine memory?
One suggestion is this: the apparent memory not only has to match something that actually happened, it furthermore has to be caused in the right way. If the experience of doing X leaves some physical traces in your brain, and as a result of those traces, you later seem to remember doing X, that would count as a genuine case of memory. If, however, your apparent memory matches the face of Joe Schmoe, whom you've had no causal contact with, then your apparent memory doesn't count as a genuine case of memory. If a hypnotist causes you to seem to remember doing X, that would not count as a genuine case of memory, either. In the first case, your apparent memory is causally connected in the right way to an original experience that it's a memory of. In the Joe Schmoe and the hypnotist cases, it is not.
Now, consider the case where you pull the cat's tail, and the experience of doing this leaves some physical traces in your brain. Suppose it's possible to remove those physical traces from your brain, and to implant them in Maria's brain. Maria would then seem to remember pulling the cat's tail. However, Maria never did pull the cat's tail. You are the one who pulled the cat's tail. So we wouldn't say that Maria remembers pulling the cat's tail. She can't remember pulling the cat's tail because she never did pull the cat's tail. But Maria is having an experience very much like memory. We can call it quasi-memory.
Maria quasi-remembers an event E iff: (i) she seems to remember E, (ii) E did in fact take place, and (iii) her apparent memory of E is caused in the right way by traces left by some person's witnessing or performing E (however, that person need not be Maria herself).
Notice that quasi-remembering does not just mean "seeming to remember." To quasi-remember an event, conditions (ii) and (iii) also have to be fulfilled. Notice also that every genuine memory is also a quasi-memory. One's memories are simply quasi-memories of one's own past life. Maria in addition has quasi-memories of (parts of) someone else's life.
What is important for our purposes is that it's possible to quasi-remember an event without being identical to the person who witnessed or engaged in that event. So the notion of quasi-memory does not presuppose the notion of personal identity.
Yet, perhaps enough links of quasi-memory among a chain of person stages would be enough to unite those stages into a single person. That is the idea behind Proposal #5. Proposal #5 modifies Proposal #4 by replacing the notion of memory with the notion of quasi-memory:
Proposal #5: 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 quasi-remember (or are able to quasi-remember) "from the inside" (enough details of enough) events experienced by the immediately preceding stages.
There is no circularity problem here. Quasi-remembering some event does not require you to be identical to the person who witnessed or engaged in that event.
To enable us to state Proposal #5 more succinctly, let's introduce the notion of psychological continuity. We say that a chain of person stages are psychologically continuous iff all of the later stages in the chain quasi-remember (or are able to quasi-remember) "from the inside" events experienced by the immediately preceding stages. Then Proposal #5 can be stated as follows:
Proposal #5: Stage A* and stage B* are parts of the same person iff they are parts of a chain of psychologically continuous person stages.
(Sometimes additional conditions are also placed on psychological continuity. For instance, we might require that the stages undergo only piecemeal and gradual changes in their personality, opinions, and interests.)
To properly assess Proposal #5, we need to introduce some new ideas. That's what we'll do next.