What Makes You You
5. Against the Psychological Descendant Account 1 Arguments from Discontinuity
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
TOTAL AMNESIA
Jiwoo is stranded on a deserted island. Adding injury to insult, a coconut fell on Jiwoo’s head at noon today, instantly resulting in total amnesia. She can’t remember how she got on the island or anything else about her past. She can’t even remember her own name.
To see why this case is supposed to pose a problem for the Psychological Descendant Account, notice that the non-amnesiac immediately before the coconut strike has very different psychological features from the amnesiac immediately after the coconut strike. This would seem to imply that the amnesiac is not a psychological descendant of the non-amnesiac, in which case the Psychological Descendant Account implies that the amnesiac isn’t the same person as the non-amnesiac. But the amnesiac clearly is the same person as the non-amnesiac. After all, the coconut doesn’t kill Jiwoo. But if she’s still around after noon, that means someone on the island after noon must be the same person as her.
And the only person on the island after noon is the amnesiac.
Jiwoo is the amnesiac.
I’ve just argued that TOTAL AMNESIA is a counterexample to the Psychological Descendant Account. But I can imagine a plausible reply from a defender of the Psychological Descendant Account. Such a defender might say that the amnesiac is a psychological descendant of the non-amnesiac. To be a descendant, the idea goes, it’s enough for their psychological features to be “mostly the same” before and after the coconut strike. But, differences in memory notwithstanding, there is still a great deal of overlap. The amnesiac and the non-amnesiac both love crossword puzzles, both are afraid of sharks, both have slightly blurry vision (since both are near-sighted), both have an easygoing temperament, and so on. All this similarity in their other psychological features, the idea goes, is enough for their psychological features to count as “mostly the same.”
Rather than trying to challenge the claim that there is sufficient overlap in TOTAL AMNESIA to count as a case of descendance, I’ll instead shift to a new case, one in which there is no overlap in the mental states, thus rendering this response unavailable. Here is the new case:
TOTAL BLACKOUT
Minjun is stranded on a deserted island. Adding injury to insult, a coconut fell on Minjun’s head at noon today, temporarily knocking him unconscious. While unconscious, he is not dreaming, nor does he have any thoughts or experiences or any physical sensations whatsoever. He is completely blacked out. When he finally awakens hours later, it will feel as if no time has passed.
Here is how to turn the case into an argument against the Psychological Descendant Account:
The Blackout Argument
(BL1) The unconscious man is not a psychological descendant of the conscious man
(BL2) If the unconscious man is not a psychological descendant of the conscious man, then: if the Psychological Descendant Account is true, then the conscious man is not the same person as the unconscious man
(BL3) The conscious man is the same person as the unconscious man
(BL4) So, the Psychological Descendant Account is false
The idea behind BL1 is that the conscious man has a wealth of sensations and emotions and thoughts and desires, whereas the unconscious man has no mental states at all. So, there is no overlap whatsoever in their psychological features. BL2 is reporting an implication of the Psychological Descendant Account:in order to be the same person, on this account, one must be a psychological descendant of the other. And BL3 seems obviously true. One would be right to point to the unconscious man lying on the island and say: that’s Minjun, the very person who was wandering the island earlier today.
5.2 The Argument from Fission
I turn now to a second argument against the Psychological Descendant Account, for which I will once again recruit the help of our neurotechnologist from section 4.2:
DOUBLE TROUBLE
Rachel’s rewiring program has been tremendously successful, and she is now performing dozens of body swaps a day. But she’s starting to get a little sloppy. Today, after rewiring Chad’s brain to duplicate JoJo’s, Rachel then accidentally rewires Alex’s brain to duplicate JoJo’s as well. As a result, both the person with Chad’s original body and the person with Alex’s original body wake up and say ‘my name is JoJo’.
Both can tell you all about JoJo’s past; neither can tell you anything about Chad or Alex’s past. Rachel’s team also accidently obliterates JoJo’s original body.
Figuratively speaking, JoJo’s mind has “fissioned” like an amoeba, into two separate bodies. But strictly speaking, how are we supposed to describe what’s happened? In particular, who’s who after the procedure, and which person (if any) is JoJo?
I’m honestly not sure what to think about the case. But one thing I am sure of is that the Psychological Descendant Account provides us with an incoherent account of what’s happened, and therefore must be incorrect. The problem, in short, is that both of the people who wake up after the procedure are psychological descendants of JoJo. If the Psychological Descendant Account is right, then that means that both of them are JoJo. But that, I contend, is impossible.
Before we state the argument more explicitly, it will again be helpful to introduce some abbreviations. Let’s use “ChadRW” to refer to the person with the rewired brain in Chad’s original body and “AlexRW” for the person with the rewired brain in Alex’s original body. Now we can state the argument against the Psychological Descendant Account as follows:
The Fission Argument
(FS1) If the Psychological Descendant Account is true, then JoJo is the same person as ChadRW and is the same person as AlexRW
(FS2) If JoJo is the same person as ChadRW and the same person as AlexRW, then ChadRW is the same person as AlexRW
(FS3) So, if the Psychological Descendant Account is true, then ChadRW is the same person as AlexRW
(FS4) ChadRW is not the same person as AlexRW
(FS5) So the Psychological Descendant Account is false Let’s take the premises one at a time.
FS1 is indisputable. The psychological features of ChadRW and AlexRW when they first wake up are virtually indistinguishable from those of JoJo, that is, the woman calling herself ‘JoJo’ just prior to the rewiring. In the minutes and hours that follow, ChadRW and AlexRW will of course begin to diverge psychologically from one another. Indeed, they’ll likely begin diverging from one another the moment they wake up! But they will remain psychological descendants of JoJo, linked by an ever- growing, moment-by-moment chain, with each “link” in the chain exhibiting massive psychological overlap with the preceding link.
And that’s all we need in order to get FS1. For, so long as each is a psychological descendant of JoJo, the Psychological Descendant Account will entail that each of them is the same person as her.
FS2 follows from a highly plausible logical principle: the transitivity of identity. According to this principle, if A = B and B
= C, then it follows that A = C. (Here, the ‘=’ symbol signifies numerical sameness.) That’s true no matter what you plug in for
‘A’, ‘B’, and ‘C’. Suppose you find out that Chadwick Boseman is the actor who played the Black Panther, and you also find out that the actor who played the Black Panther was also the star of Ma Rainey’s Black Bottom. You wouldn’t then wonder whether Chadwick Boseman is the same person as the star of Ma Rainey’s Black Bottom. That’s because you already have all the information you need in order to deduce that it’s the same guy: if Chadwick Boseman = the actor who played the Black Panther, and the actor who played the Black Panther = the star of Ma Rainey’s Black
Bottom, then (by the transitivity of identity) Chadwick Boseman = the star of Ma Rainey’s Black Bottom. By that same indisputable logic, if ChadRW = JoJo and JoJo = AlexRW, then ChadRW = AlexRW. That’s what gives us FS2.
Premise FS4 is motivated by a different logical principle, which I’ll call ‘The No Difference Principle’, or ‘NDP’ for short:
(NDP) If A is numerically the same as B, then at any given time, anything that’s true of A at that time is also true of B at that time
To illustrate the principle, consider Cassius Clay and Muhammad Ali. Cassius Clay is Muhammad Ali, they’re numerically the same. Here’s something that was true of Ali: he was in a boxing ring on October 30, 1974 at 10pm. So, by NDP, the same must be true of Clay: he too was in a boxing ring at that time. And that’s just as it should be. ‘Cassius Clay’ and ‘Muhammad Ali’ are just two names for one and the same guy, so it can’t very well be that
“one of them” is in the boxing ring and “the other one” isn’t.
There’s just the one guy, and he either was or wasn’t in the boxing ring at that time.
This principle, NDP, is also a useful tool for demonstrating that two people aren’t numerically the same. NDP tells us that if, at a given time, you can find even a single difference between A and B, then A and B cannot be numerically the same. If you’re wondering whether Emily and Haley are the same person, just notice that Emily is skydiving right now and Haley isn’t, and that settles it: they must be two different people. If they were numerically the same, then anything true of the one would have to be true of the other. But it’s true of Emily that she’s skydiving and that isn’t true of Haley. So, by NDP, they must be two different people.
Exactly the same logic applies in the case at hand. If you’re wondering whether ChadRW and AlexRW are the same person, just notice that ChadRW is currently walking down the street and AlexRW isn’t currently walking down the street. (AlexRW is still in Rachel’s lab, staring at the ceiling.) That settles it: no one person can both be and not be walking down the street. So ChadRW and AlexRW must be two different people, just as FS4 says.
I can imagine someone objecting to FS4 by saying that after the rewiring, JoJo is a single person with two bodies. If that were true, that would mean that she has four eyes, two of which are looking down at the sidewalk and two of which are looking up at the ceiling. If you ask her “are you walking down the street right now?” she might say yes or she might say no, depending on which of her two bodies you ask. But when Alex’s original body (which is in the lab) answers ‘no’, that’s a mistake according to the view in question. For on this view, AlexRW is walking down the street, since AlexRW—the person with Alex’s original body—is a person who has two bodies, one of whose bodies—the one that used to belong to Chad—is walking down the street. So, the idea goes, we don’t have a case of a single thing with conflicting properties after all, thus clearing the way to denying FS4 and insisting that ChadRW and AlexRW are the same person, namely JoJo.
This is an incredibly weird way of thinking about the DOUBLE TROUBLE case. And it can’t be right, for the very same reasons that it can’t be right to say that conjoined twins Abby and Brittany are the same person (see section 4.1). Suppose that ChadRW goes on to marry a man named ‘Emir’. Emir later kisses AlexRW, and then kills ChadRW so he can be with AlexRW. If ChadRW and AlexRW were the same person, then Emir isn’t cheating on ChadRW, since Emir was kissing ChadRW (a.k.a. AlexRW); and Emir didn’t kill anyone, since ChadRW is AlexRW, and ChadRW is still alive (all Emir did, on this view, is destroy one of ChadRW’s two bodies). But surely that’s wrong. Emir did cheat on ChadRW, and the district attorney would be right to charge him with homicide—all of which presupposes that FS4 is right, and that ChadRW and AlexRW are two different people.