# Phil 101: Responding to the Fission Objection

## Proposal #6

Dave Cohen responds to Gretchen’s criticism 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.

The defenders of proposals like Proposal #5 and Proposal #6 are often referred to as “psychological continuity theorists.” 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 “at least as close competitor” stages, not part of the chain, which are also psychologically continuous with A*, then A* and B* are parts of the same person.

That view is known as the “closest competitor theory”.

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. Proposals #7 and #8 aren’t discussed, though they are natural variations on the views that are discussed. I will postpone discussion of these alternatives to Proposal #6 until the lecture notes for Perry’s Third Night.

### Objections to Proposal #6

Proposal #6 is the most sophisticated of the accounts we’ve seen so far. But that does not make it immune to criticism. On pp. 34-36, Gretchen advances several objections to this proposal.

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 or “supervene on” what the chain connecting A* and B* is like, intrinsically. Facts about other chains should not be relevant. (Think about whether this objection also applies to Proposals #7, #8, or #9.)