What Makes You You
4. Against the Same Body Account
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.
disorder, a.k.a. “multiple personality disorder.” Isn’t this a case of more than one person having numerically the same body?
Perhaps. But it’s not entirely clear to me that that’s right way to understand the disorder. Another way of thinking about such cases is that there is a single person with a highly disunified mind, a single person who feels and behaves dramatically differently at different times. In any event, I would want to know a lot more about what it is like “from the inside” for those suffering from this disorder before I am prepared to say that such cases literally involve multiple people inhabiting a single body. For that reason, I will set such cases aside and focus on cases that much more clearly pose a problem for the Same Body Account.
4.1 Conjoined Twins
The first objection I’ll raise against the Same Body Account involves conjoined twins. Abby and Brittany Hensel are dicephalic parapagus twins, which means there are two heads on a single torso. They are alive and well and are currently about 30 years old. It’s easy to see why conjoined twins pose a problem for the Same Body Account. We would naturally describe Abby and Brittany as two people sharing a single body. But the Same Body Account rules that out, since it says that sharing a body is sufficient for being the same person.
We can make the argument more explicit as follows:
The Conjoined Twins Argument
(CT1) If the Same Body Account is true, then either Abby and Brittany have different bodies or Abby and Brittany are the same person
(CT2) Abby and Brittany have the same body (CT3) Abby and Brittany are not the same person (CT4) So, the Same Body Account is false
CT1 is merely reporting an implication of the Same Body Account. If same body entails same person, then that either means that Abby and Brittany are two different people in two different bodies or the same person in the same body. Those are the only two ways it can be according to the Same Body Account. CT2 seems true: what we have here is a single, two-headed human
organism. (Indeed, there’s a documentary on Abby and Brittany titled, “The Twins Who Share a Body.”) And CT3 seems right as well: Abby and Brittany are different people. Among other things, they have different preferences in food and they excelled in different subjects in school. I bet you didn’t even flinch when I said ‘they’ as opposed to ‘she’.
I can imagine someone denying CT2 and insisting that, actually, there are two bodies there, split down the middle. First, there’s Abby’s body, consisting of the right arm, right leg, right lung, the right head (the one that says “my name is Abby”) and so on. Second, there’s Brittany’s body, consisting of the left arm, left leg, left lung, left head, and so on.
I find that completely implausible. For one thing, it would entail that Brittany has no liver (since the liver is on the right side).
But surely the correct thing to say is that they share a liver, which requires that the body parts on right side are also parts of Brittany’s body. Additionally, upon encountering a two-headed snake or a two-headed turtle, you would never say that there were two bodies there. There’s just a single animal with two heads; it’s a single, two-headed body. Since that’s what we’d say about nonhuman animals, we should say the same about human animals. To be clear, I am not saying there is only one person there;
indeed, I say just the opposite in premise CT3. Rather, the claim is that there’s a single, two-headed body, which is both Abby’s body and Brittany’s body.
What about denying CT3 and saying that Abby and Brittany are the same person? That’s certainly a strange thing to say. But maybe what I said above about multiple personalities can be applied to the case of conjoined twins as well: there is just one person there, but her mind is disunified and as a result she behaves in peculiar ways, for instance saying (out of one of her mouths) “I’m good at math” and then saying (out of her other mouth) “I’m terrible at math.”
But this seems entirely implausible when applied to Abby and Brittany. To see this, consider the following case:
CONJOINED DRAMA
Abby is dating Arie. Brittany is secretly in love with Arie and has always been jealous of their relationship. One night, while
Abby is sleeping, Brittany confesses her feelings to Arie, and Arie kisses her. Later, when Abby finds out, she strangles Brittany.
Here’s how we’d naturally describe what happened: Arie cheated on Abby and then Abby killed Brittany. Yet someone who denies CT3, and therefore says that Abby and Brittany are the same person, would have to say that this description is completely inaccurate. Arie didn’t cheat on anyone, since the person he was kissing that night was his own girlfriend Abby (a.k.a. Brittany).
Furthermore, the CT3-denier would have to say that Abby didn’t kill anyone, because no one was killed: she strangled herself and she survived (albeit with one fewer functioning head). But surely that’s not the right way to describe what happened.
4.2 Body Swaps
Here’s a second argument against the Same Body Account. This one involves an imaginary case, one which may seem familiar if you’ve read John Locke’s chapter on Identity and Diversity in his Essay Concerning Human Understanding. Or if you’ve seen Freaky Friday on the Disney Channel. The case is far-flung, but the fact that nothing like it has ever actually happened and perhaps never will (though I wouldn’t be so sure) is neither here nor there. For, as I explained in section 2, an account of personal identity cannot admit of any exceptions, even in principle.
Now for the case:
BODY SWAP
Rachel is a neurotechnologist. Using an fMRI, a supercomputer, and advanced laser technology, she has devised a way to get a complete neuron-for-neuron scan of one person’s brain, and then rewire a second person’s brain to be an exact duplicate of it. She recruits a pair of volunteers to have their wiring “swapped” for a day: a man named Raúl and a woman named June. Rachel’s team performs the procedure on Tuesday night, and the volunteers are awakened on Wednesday. Both stare down at their bodies in disbelief. The person with the male body says ‘my name is June’ and can recount all of June’s memories but knows
nothing at all about Raúl’s past. The person with the female body says ‘my name is Raúl’ and can tell you all about Raúl’s past but nothing about June’s.
I think we can all agree on how we ought to describe what is happening on Wednesday. June is now walking around with a male body, and Raúl is walking around with a female body. The alternative would be to say that June is still the person with the female body but that she is completely delusional: she mistakenly thinks her name is ‘Raúl’, and recalls doing all sorts of things that she has never actually done (but all of which Raúl has done). But that’s not what happened. No one is delusional. Rather, two sane people have switched bodies.
If that’s right, then the Same Body Account is incorrect. Before stating the argument against the Same Body Account, it will be helpful to introduce some terminology to help us talk and think clearly about the case. I’ll use “MaleT” to refer to the person with the male body on Tuesday; “FemaleT” for the person with the female body on Tuesday; “MaleW” for the person with the male body on Wednesday, and “FemaleW” for the person with the female body on Wednesday. Here, then, is the argument:
The Body Swap Argument
(BS1) MaleT and MaleW have the same body
(BS2) If MaleT and MaleW have the same body, then: if the Same Body Account is true, then MaleT and MaleW are the same person
(BS3) MaleT and MaleW are not the same person (BS4) So, the Same Body Account is false
BS1 is true: it’s the same male body that enters the lab on Tuesday and leaves the lab on Wednesday. No doubt, rewiring its brain to resemble a woman’s brain is going to affect the chemistry of that body in all sorts of ways. But that doesn’t make it a numerically different body, any more than medically modifying all your DNA gives you a numerically different body (see section 3.1). BS2 is just reporting an implication of the Same Body Account: that account entails that having the same body suffices for being the same person. And BS3 is reporting what we all find
perfectly obvious when we think about this case or when we watch a movie like Freaky Friday.
The Same Body Account yields the wrong verdict about who’s who in BODY SWAP. It wrongly entails that MaleT is the same person as MaleW. It also wrongly entails that MaleT (i.e., the one who was calling himself ‘Raúl’ on Tuesday) and FemaleW (i.e., the one insisting “I’m Raúl!” on Wednesday) are different people.
So, the Same Body Account must be rejected.
The Psychological Descendant Account, by contrast, gets the right answers in this case. FemaleW is a psychological descendant of MaleT: there is massive overlap between the psychological features of the person who woke up with a female body on Wednesday and the person who walked in with a male body on Tuesday. Additionally, MaleW is not a psychological descendant of MaleT: MaleT has virtually nothing in common psychologically with MaleW, nor is there any gradually changing chain of overlap (of the sort described in section 3.2) linking MaleT to MaleW. So, the Psychological Descendant Account again gives us the right result, that MaleT is not MaleW.
Getting one wrong result is enough to show that the Same Body Account is false. But getting a couple correct results is not enough to show that the Psychological Descendant Account is true. So, let us turn now to see whether the Psychological Descendant Account has some problematic consequences of its own. (Spoiler: it does.)
5. Against the Psychological Descendant Account