Dave Cohen responds to Gretchen’s fission objection as follows. Take a person stage A*. If at a later time there is only one person stage B* psychologically continuous with A*, then B* and A* are parts of the same person. But this is only true when there is one candidate B*. If there are several candidates B*, C*,… — all of which are psychologically continuous with A* — then some or all of them may fail to be identical to A*. Personal identity only consists in psychological continuity when there are no competitors.
Proposal #6: If A* and B* are parts of a chain of psychologically continuous person stages, and if the later stages in this chain do not co-exist with any other “competitor” stages, not part of the chain, which are also psychologically continuous with A*, then A* and B* are parts of the same person (p. 33).
One of my former students, Tom Kelly, offered the following analogy.
Take a piece of chalk, Chalky. Now suppose that as I write on the board with Chalky, it gradually gets worn down to a stub Stubby, half the size of the original piece of chalk. If I started the class holding Chalky in my hand, and end the class holding Stubby in my hand, it seems right to say that I’ve had the same piece of chalk in my hand for the course of the class. That is, it seems right to say that Chalky and Stubby are the same piece of chalk. (It’s just that this piece of chalk has gotten worn down as the class progressed.) Contrast a second case, where I hold Chalky up at the start of class, and break it perfectly in half. In my right hand I have a stub S1, and in my left hand I have a stub S2. We can imagine that S1 is exactly the same size and shape as Stubby was, in the first case. We can even imagine that S1 and Stubby are made of the same molecules. However, although in the first case it seemed right to say that Stubby is the same piece of chalk as Chalky, here it does not seem right to say that S1 is the same piece of chalk as Chalky. S1 has a competitor, S2. S1 and S2 seem to have equally good claims to be identical to Chalky; hence, we’re forced to say that neither is identical to Chalky. In the first case, though, where the stub in my right hand had no competitors, it did seem right to count that stub as the same piece of chalk as Chalky. So the presence or absence of competitors makes a difference to whether we count the stub as being the same piece of chalk as Chalky.
There are some other refinements of Proposal #5 we could consider instead. I’ll label them as follows:
Proposal #7: If A* and B* are parts of a chain of psychologically continuous person stages, and if the later stages in this chain do not co-exist with any other “competitor” stages, not part of the chain, which are also psychologically continuous with A*, and where the competitor stage is “as close or closer” to A* than B* is, then A* and B* are parts of the same person.
That view is known as the “closest competitor theory,” because it says that B* gets to be a later of stage of the person when it’s the closest of any competitor stages.
Other possible views are:
Proposal #8: If A* and B* are parts of a chain of psychologically continuous person stages, and where that chain also includes most or all of the same persisting physical body, then A* and B* are parts of the same person.
Proposal #9: If A* and B* are parts of a chain of psychologically continuous person stages, and where that chain also includes most or all of the same persisting physical brain, then A* and B* are parts of the same person.
Proposal #9 is discussed later in the Perry dialogue (see below). Proposals #7 and #8 aren’t discussed, though they are natural variations on the views that are discussed. We’ll return to these alternatives below.
Proposals like these are the most sophisticated of the accounts we’ve seen so far. But that does not make them immune to criticism. On pp. 34-36, Gretchen advances several objections to what we’re calling Proposal #6.
We will note only the first of these objections here. This is that Proposal #6 makes the answer to the question “Does the chain connecting A* and B* compose a single person?” depend on matters extrinsic to that chain. Whether A* and B* count as parts of a single person will depend on whether B* has any competitors — that is, on whether there are any other person stages elsewhere in the universe which are also psychologically continuous with A*. But this seems wrong-headed. The facts about whether A* and B* are parts of the same person shouldn’t turn on what other chains of person stages exist elsewhere in the universe. Personal identity should be an intrinsic matter. It should only depend on what the chain connecting A* and B* is like, intrinsically. Facts about other stages and other chains should not be relevant. (Think about whether this objection also applies to Proposals #7, #8, or #9.)
One response to these puzzles is to say that we just need to make a decision, about which person we’re going to call “the same person” as you. This move is discussed during Perry’s Third Night (on pp. 40-42). We’ve already discussed this move, and why it’s unsatisfactory. We’ll be talking about it again when we read Williams and Parfit.
A second way of responding to these puzzles is to argue that one kind of basis for judgments about personal identity is more important than the other kind of basis. This is what Sam Miller and Dave Cohen attempt to do next, on pp. 42-44. They argue that “Lockean”/psychological continuity theories of personal identity have several advantages over theories that count having the same body as more important.
One advantage they claim for psychological continuity theories is that these theories can explain how it is possible to have reasonable beliefs about one’s own identity, without examining anything but one’s own mind. (Normally, one does not bother to check and see if one has the same body, before one judges oneself to be the same person as an earlier person.)
A second advantage they claim for psychological continuity theories is that these theories explain why we care about personal identity, why it is important to us. For on psychological continuity theories, personal identity consists in the preservation of one’s personality and memories — and these are the sorts of properties that we value very highly. We regard personal identity as important because it consists in the preservation of properties that we value highly.
Gretchen allows that Proposal #5 can fairly claim to have these advantages. However, Proposal #5 gives the wrong answer about fission cases. In a fission case, the most sensible thing to say is that the original person is not identical to either of the resulting persons. But Proposal #5 does not permit us to say that.
In order to accommodate fission cases, the psychological continuity theorist has to adopt some more complicated proposal, like Proposal #6, which says that personal identity consists in psychological continuity plus the absence of any competitors. Or perhaps the psychological continuity theorist could instead go with what we called Proposal #9:
Proposal #9 (Brain-Based Psychological Continuity Theory): Stage A* and stage B* are parts of the same person iff they are parts of a chain of psychological continuous person stages, where that psychological continuity is secured by the presence of one and the same brain in every stage. (Dave Cohen may be suggesting Proposal #9 very quickly on p. 47 of the dialogue.)
In Proposal #9, the requirement that all the stages have the same brain guarantees that the later stages have no competitors. Why? Because if B* has the same brain as A*, then any other stage existing at the same time as B* would have to have a different brain. So Proposal #9 is like Proposal #6 in that it makes personal identity a matter of psychological continuity, plus an absence of any competitors. It is just more specific about how the absence of any competitors is to be secured.
At the end of the Third Night (pp. 47-8), Gretchen argues that if the psychological continuity theorist adopts Proposal #6 or Proposal #9, then the supposed advantages that Sam and Dave claimed for psychological continuity theory disappear.
On Proposal #6 and Proposal #9, it is no longer true that one can have reasonable beliefs about one’s own identity, without examining anything but one’s own mind. One also has to check the world, to see whether one has any competitors, or to see whether one still has the same brain one used to have.
Likewise, on Proposal #6 and Proposal #9, it is no longer true that personal identity consists just in the preservation of one’s important psychological features. If you step into a teletransporter which “scans” your body and your brain without destroying them, and creates a perfect copy of you on Mars, the copy on Mars will not be identical to you, according to either of these two proposals. He has a competitor (the person who remains on Earth), and he does not have the same brain as you (he has a copy of your brain). Nonetheless, the copy on Mars will have all the important psychological features you have. So on these two proposals, having the same important psychological features does not suffice for identity. It is not clear, then, that these proposals are in any special position to explain why we regard personal identity as so important.
Hence, Gretchen prefers to remain with an account like Proposal #2, which said that personal identity is a matter of having the same body. Or perhaps we should go with an account like the following:
Proposal #3: Stage A* and stage B* are parts of the same person iff they have the same brain. It is not necessary that they also be psychologically continuous. (This proposal is very similar to Proposal #2, but is not discussed in the Perry dialogue — unless it’s what Dave meant on p. 47.)
On both Proposal #2 and Proposal #3, one can survive total and irreversible amnesia. On psychological continuity theories, on the other hand (proposals starting with #4), one cannot survive amnesia of that sort, because it destroys psychological continuity. Which views do you think are more plausible?
On Proposals #2, #8 and #9, and #3, one cannot survive teletransportation, even in “optimal” or straightforward cases of teletransportation, where no competitors ever exist at the same time. Why not? Because teletransportation destroys one’s brain and body, and creates a replica of them on Mars. These proposals deny that a person can survive changes which involve coming to have a wholly new brain and body, all at once.
According to defenders of Proposals #2, #8, #9, and #3, a teletransporter is not a device for transporting a single person great distances. Rather, it’s a device for killing one person and creating a duplicate of that person in his or her place.
Defenders of Proposal #6 disagree. (So too do defenders of the “closest continuer” theory, which we called earlier called Proposal #7.) These theorists admit that, when the teletransporter produces two copies, the person who went into the teletransporter is not identical to either of the resulting persons (because the two copies compete with each other). But they would say that, so long as the teletransporter only produces one copy on Mars — and the original is destroyed before the copy is created — then the person who went into the teletransporter is identical to the person who comes out on Mars.
But the defenders of Proposals #2, #8, #9, and #3 say that the person who goes into the teletransporter is never identical to the person who comes out on Mars.