What Makes You You
3. Some Promising and Unpromising Answers 1 Physical Answers
TRACE is enough to show that the Fingerprints Account is no good. That’s because what we’re looking for is an account of personal identity which has no exceptions even in principle. The same is true for other accounts which we will consider below:
even merely hypothetical examples can serve as counterexamples to those accounts. (For more on how merely hypothetical cases can still be relevant when assessing philosophical claims, see section 7 of the Introduction to this textbook.)
3. Some Promising and Unpromising Answers
The DNA Account does get around some of the problems that arise for the Fingerprints Account. Bekah’s DNA doesn’t change at all before and after searing off her fingerprints, so the DNA Account delivers the correct verdict that pre-searing Bekah is the same person as post-searing Bekah.
But the DNA Account has problems of its own. Identical twins have indistinguishable DNA, but this doesn’t make them the same person. (Any identical twins reading this are now nodding along vigorously. In unison.) So, having indistinguishable DNA isn’t sufficient for being the same person.
Nor is it necessary. There could, at least in principle, be a medication or performance-enhancing drug you can take that would make some small change to the DNA in every cell of your body. But it would still be you after you took the medication, even though your DNA would be somewhat different.
Still, these answers may be on the right track by focusing on some physical aspect of you. Perhaps, instead of focusing on some small part of your body, like your fingerprints or DNA, we would do better to focus on the body as a whole:
The Same Body Account
Aat tis the same person as B at t* if and only if A has the same body as B
‘Body’ is sometimes used to mean just the torso, not including the head and limbs. That’s not how I’m using it. When I say ‘body’, I mean the whole body, including the head and all the other body parts. And when I say that A and B have the same body, I mean that they have numerically the same body. Bodies obviously can change over time—indeed, your body was composed of almost entirely different cells seven years ago—but that’s not to deny that the body you have now is numerically the same as the body you had seven years ago. It’s not as if you used to have some other arms and legs and now you have entirely new ones!
The Same Body Account is going to avoid all the other problems we mentioned, since you have the same body even if your fingerprints or DNA change, and separate people with indistinguishable DNA or fingerprints don’t have numerically the same body. It’s true that your body won’t be exactly the same
qualitatively after your DNA changes, but what’s required by the Same Body Account is numerical sameness, not qualitative sameness. The body is numerically the same after the DNA changes.
3.2 Psychological Answers
We’ll see in the next section that the Same Body Account has problems of its own. But before getting there, we should also consider a different sort of account, one framed in terms of people’s psychological features as opposed to their physical features. By ‘psychological features’, I mean to include any features of a person’s mental life: their memories, their personality, their likes and dislikes, their beliefs, their emotions, and even their current perceptual experiences (how things look, sound, smell, and feel to them).
So how should we formulate an answer to the question of personal identity in terms of psychological features? As a first stab, we might consider the following account:
The Psychological Matching Account
A at t is the same person as B at t* if and only if A’s psychological features are exactly the same as B’s psychological features
But this Psychological Matching Account is obviously far too demanding. Every second that passes, you are forming new memories. For instance, you now have a memory of reading the previous sentence, but you had no memory of it a minute ago (since you hadn’t yet read it a minute ago). You also have slightly different visual experiences now than you had a minute ago, since you’re now looking at different words on the page. Accordingly, the Psychological Matching Account is going to say that the person sitting in your chair a minute ago and the person sitting in your chair now are two different people. But that’s absurd! It was you that was sitting in the chair a minute ago.
To get around this problem, we might try to loosen things up, so that the account doesn’t require people at different times to have all the same psychological features, but only that they have mostly the same psychological features.
The Psychological Overlap Account
A at t is the same person as B at t* if and only if A’s psychological features are mostly the same as B’s psychological features
The Psychological Overlap Account avoids the previous problem.
You may not have all the same psychological features you had a moment ago, but you do have mostly the same psychological features (beliefs, memories, personality, etc.).
But the Psychological Overlap Account gets the wrong results when we reach back further into the past. You and that kid in the photo are the same person. That’s you in the photo. But your current psychological features and the kid’s psychological features when the photo was taken aren’t mostly the same. The kid’s personality and likes and dislikes are completely different from yours. You have very few of the same memories, since you’ve forgotten much of what the kid remembers at that time, and the kid at that time hasn’t yet formed most of the memories you now have. So, the Psychological Overlap Account is going to yield the wrong verdict: it says that the kid in that photo isn’t you.
What we need is something even more flexible, something that can accommodate the fact that, over a long period of time, a person can gradually undergo a massive change in their psychological features. But we don’t need to abandon the notion of psychological overlap entirely. Rather, we can use it to define the new, more flexible notion that we need.
To see the way forward, notice that, even though there isn’t much overlap between your current psychological features and your psychological features at the time the photo was taken, there is a great deal of psychological overlap between you now and you a year ago. And there’s a great deal of overlap between you a year ago and you two years ago. And between you two years ago and you three years ago. And so on, going all the way back, year-by- year, to you at age six and the five-year-old in the photo. We can picture this as a long chain—running from you now to that five- year-old—where each link represents a “snapshot” of your psychological features at some time, and each link in the chain has mostly the same psychological features as the links immediately
before and after it. And the chain needn’t be year-by-year; it can be day-by-day or even moment-by-moment.
When there is such a moment-by-moment chain of overlap linking a person at one time to a person at a later time, I’ll say that the person at the earlier time is a psychological ancestor of the person at the later time, and that the person at the later time is a psychological descendant of the ancestor. This gives us:
The Psychological Descendant Account
A at t is the same person as B at t* if and only if A is either a psychological ancestor or a psychological descendant of B This gives us the right results in all of the cases we have been considering. You are a psychological descendant of the kid in the photo, despite sharing very few psychological features with that kid; Bekah pre-searing is a psychological ancestor of Bekah post- searing; and so on.
We now have two different, initially promising answers to the question of personal identity: the Same Body Account and the Psychological Descendant Account. It may seem like an embarrassment of riches. They both look great, so how are we supposed to choose between them? As we are about to see, however, both answers are deeply flawed, and we should not accept either of them.