耶魯大學(xué)開放課程——哲學(xué)：死亡Death 13

Death: Lecture 13 Transcript

February 27, 2007 8

Professor Shelly Kagan: Let me start by reviewing the problem that we were considering last week. We were raising a difficulty for the personality theory of personal identity according to which the key to being the same person is having the very same ongoing, evolving personality. And the difficulty was basically the problem of duplication. That it seemed as though we could have more than one--call it an individual--more than one body, that had the very same set of memories, beliefs and so forth. And that we have to ask ourselves, "Well, what should the personality theory say about a case like that?"

So imagine that over the weekend, the mad scientist copied my memories, beliefs, desires, fears, ambitions, goals, intentions and imprinted that on somebody else's brain. They did it last night at midnight. This morning, we woke up. And we have to ask ourselves, "Who's Shelly Kagan? Who's the person that was lecturing to you last week?" Well, it doesn't seem plausible in terms of the personality theory to say that he's Shelly Kagan, and the one here today--Suppose the other one's in Michigan. If the one in Michigan's Shelly Kagan but this one's not--After all, although it's true that he's got Shelly Kagan's memories, he woke up thinking he was Shelly Kagan, just like I woke up thinking I was Shelly Kagan. He woke up thinking about what he was going to lecture on in class today, just like I woke up thinking about what I was going to lecture in class today. He remembered last week's lecture just like I remembered last week's lecture.

Well, no clear reason to say--for the personality theory to say--that he's Shelly Kagan and I'm not. After all, I've got the very same set of memories, beliefs, desires that he has. But equally true, and more surprisingly, from the personality theory point of view, there's no reason to say that I'm Shelly Kagan and he's not. After all, he's got all the same memories, beliefs and desires that I do. It doesn't seem plausible to say we're both Shelly Kagan, because now we'd have to then say Shelly Kagan's in two places at the same time. So the only alternative seems to be to say that neither of us is Shelly Kagan. But if neither of us is Shelly Kagan, then the simple original personality theory was false. Because according to that theory, having the personality is what it took to be Shelly Kagan. We both have it, yet neither of us is Shelly Kagan. The personality theory must be false.

So we revise the personality theory to say, the secret to personal identity is having the same personality--provided that there's no branching. Provided there's no splitting. Provided there's only one best competitor, not two equally good candidates. Given the no branching view, the no branching rule, we can say, in the ordinary case, look, there really wasn't anybody imprinted with my memories and desires in Michigan. I'm the only one around in the earth right now with Shelly Kagan's memories and desires. Since there's no competitor, and I've got the personality, I'm Shelly Kagan. I'm the very same person that was here lecturing to you last week. That's what the personality theory--It gives us the answer we're looking for in the ordinary case. But in the science fiction story where there's a duplicate, it says, uh, if there's branching, the no branching rule comes in. Neither of them is Shelly Kagan.

All right, so that's the best way for the personality theory to get revised to deal with this problem. The trouble was, it seems the no branching rule seems very counter-intuitive. So think about it. Here, right now I'm standing in front of you saying I'm Shelly Kagan, the guy who was lecturing to you last week. I believe I'm Shelly Kagan, the guy who was lecturing to you last week. Am I Shelly Kagan? Well, I've got Shelly Kagan's personality. So far so good. Now all we have to decide is, was the branching rule satisfied or violated? So all we have to know is, is there somebody else somewhere in the universe who's got all my memories and beliefs and desires? Well, how in the world could I know that?

Whether I, this person talking to you right now, is Shelly Kagan depends on whether there's some duplicate with all my memories in Michigan or not? It seems very counter-intuitive. So although the personality with no branching rule avoids the problem of what to say about duplicates, by saying when there's branching, neither of them is Shelly Kagan, the branching rule itself seems very counter-intuitive. We feel as though whether somebody is me or not should depend upon internal facts about me in the earlier stages or this stage and that stage, not about what's happening elsewhere, outside, extrinsic to these things. So, if you're not willing to accept the no branching rule, if it strikes you as a bizarre thing to throw in to personal identity, maybe you need to reject the personality theory.

Now during all of this, the fans of the body view typically are laughing. They say this just goes to show what a dumb theory the personality theory is. The whole problem with the personality theory is that personality is a bit like a software. It's like programs. It's the various programs you run on your computer along with the various data files that you have saved on your hard drive, and so forth. And those can be duplicated. You have copy after copy after copy. You can have two copies of my personality. You could have 100 or 1,000. The problem with--what drove the personality theory into the no branching rule, implausible as it may be, was the fact that your personality is like software, and it can be copied."

That's why, they say, we should believe in the body view. If we accept the body view, we avoid the duplication problem. Because, unlike software, which can be literally copied, as many as you want identical, the body can't split. Human bodies can't divide or branch. There's no way that there's another body, that the body on Thursday became two bodies. The body that was here on Thursday didn't, couldn't become two bodies. So we avoid all the problem. That's at least the kind of claim that fans of the body view often make in the face of this difficulty for the personality theory.

Well, now we need to ask, is it really true? Is it really true that bodies don't face a duplication problem? Is it really true that human bodies don't and couldn't split? Look, the crucial word here is, of course, "couldn't." Personalities don't actually split either, right? Although I've been giving science fiction examples in which the mad scientist duplicates my memories and beliefs and desires, they've all been science fiction examples. If I can use science fiction to talk about the possibility of splitting, and use that against the personality theory, I'm entitled to use science fiction examples to talk about the possibility of bodies splitting, and ask, what kind of problem that would raise for the body theory?

Now, we are familiar with some low-level examples of bodies splitting. Amoebas split, right? You've got a single amoeba. It's going along. At a certain point--Let's draw our amoeba splitting, right? [See Figure 13.1] You've got an amoeba split, going along. At a certain point, it starts to look like that. Then it looks like that. And then boom! You've got, well, it splits. There's nothing in biology per se that rules out cell division. Indeed, on the contrary, right? We know cells can split. Now, human bodies, unlike amoebas, don't do that. But maybe there's nothing in biology that rules out the possibility. Suppose we open up the Yale Daily tomorrow and we see that the Yale Center for Amoebic Studies has made this tremendous breakthrough and has discovered how to, through the right kind of injection or whatever, cause a human body to replicate and split in an amoeba-like fashion. Well, then we have to face the problem of what to say in this case of bodily branching.

Well, instead of pursuing that example, let me give you a slightly different example that's been discussed a fair bit in the philosophical literature. This is actually a case that one of the students in the class asked about, I think it was last week, if it wasn't even earlier. And I said, "Great question. Let's come back to it." So here, at long last, I'm making good on my promissory note. I'm going to come back to the example that was raised before

You'll recall that when we talked about the body view, I said the best version of the body view doesn't require the entire body, to be the same body, but the brain. Follow the brain. And indeed, it doesn't seem as though we have to require the entire brain, just enough of the brain, however much that turns out, to house personality, memories and so forth. And then, I said, suppose it was possible that one hemisphere of your brain is enough. If there's enough redundancy in the brain so that even if your right hemisphere got destroyed, your left hemisphere, you still have all the same memories, desires, beliefs. Good enough.

So now we worry about the following case. So I gave you a bunch of examples, right, where there are brains being transplanted into torsos of others. So suppose, gruesome as it was, this weekend I'm in some horrible accident and my torso gets destroyed and they keep my brain on life support, oxygenating it just long enough to do some radical surgery into some spare torsos. Where'd the torsos come from? Well, you had some living people, but they had very rare brain diseases and their brain suddenly liquefied. So now we've got some spare torsos.

All right, so here we've got Shelly Kagan. His body gets destroyed. And here's my brain. Over here we've got Jones' torso. And over here we've got Smith's torso. Suppose we take, call this one the left hemisphere, and we stick it in here, into Jones' torso. We take this other hemisphere, the right half of my brain and we stick it into Smith's torso. We connect all the wires, all the neurons. The operation's a smashing success. Both things wake up. So here's Jones' torso with the left half of SK's brain. Smith's torso with the right half of SK's brain. They wake up. We need some way to refer to these people, so we can start talking about who they are. Let me just call this top one--Jones' torso with the left half of Shelly Kagan's brain--let's call him Lefty. Smith's torso with the right half of Shelly Kagan's brain, let's call him Righty. [See Figure 13.2]

Okay, operation's a success. Lefty and Righty both wake up. They both think they're Shelly Kagan, and so forth and so on. And we ask ourselves, according to the body view, which one is Shelly Kagan?

What are the possibilities? We could say Lefty is Shelly Kagan and Righty is not. Righty's an imposter. But there's nothing in the body view to give us a reason to make that choice. It's true that Lefty's got half of Shelly Kagan's brain and that's good enough. But it's also true that Righty's got half of Shelly Kagan's brain and that seems good enough. So there's no reason to say that Lefty is Shelly Kagan and Righty isn't. And similarly, of course, there's nothing in the body view to make us say that Righty is Shelly Kagan and Lefty isn't.

Well, if it's not one, and not the other, what are the remaining possibilities? We could, I suppose, try to say they're both Shelly Kagan. And so Shelly Kagan continues, that is to say his body continues, that is to say his brain continues, that is to say enough of his brain continues, merrily on its way, except now in two places. And so from now on, Shelly Kagan, that single person, is in two different places at the same time. Lefty goes to California. Righty moves to Vermont. From now on, Shelly Kagan's bicoastal. It doesn't seem right.

So what else can the body theory say? Well, the body theory could say neither of them are Shelly Kagan. Shelly Kagan died in that gruesome, horrible accident. Although it's true that we now have two people, Lefty and Righty, each of whom has half of Shelly Kagan's brain, and all of Shelly Kagan's memories, for whatever that's worth, neither of them is Shelly Kagan. We could say that as well. But if we--and that seems the least unpalatable of the alternatives. But if we say that, then we've given up on the body view. Because the body view, after all, said to be Shelly Kagan is to have enough of Shelly Kagan's brain. And in this case, both of Lefty and Righty seem to have enough of Shelly Kagan's brain. What's the body theorist to do?!

As far as I can see, the best option for the body theorist at this point is to add--no surprises here--a no branching rule. The body theorist should say, "The key to personal identity is having the same body, to wit, the same brain, to wit, enough of the brain to keep the personality going--provided that there's no branching, no splitting, no perfect competitors, only one." If the body view adds the no branching principle, then we can say, look, in the case of this sort of splitting--This example is known in theto philosophical literature as fission, like nuclear fission when a big atom splits into two. So, in the fission case, the body says, the body theorist says, in the fission case, there's splitting, there's branching. So neither of them is going to end up being Shelly Kagan.

But in the ordinary humdrum case, here I am, my body. Why am I Shelly Kagan? Because the brain in front of you--you can't see it, but it's in front of you--the brain in front of you is the very same brain as the brain that you had in front of you on Thursday. Follow the body, in particular follow the brain. So in the ordinary case, no splitting, follow the brain. In the special case where there's splitting, even if you follow the brain, not good enough. So the body theorist can avoid the problem of fission, avoid the problem of duplication by adding the no branching rule.

But of course, the no branching rule didn't seem very intuitive. Whether or not I'm Shelly Kagan, the guy that was lecturing to you on Thursday, depends on whether, unbeknownst to me, over the weekend, somebody removed half of my brain, stuck it in some other torso, sealed me all back up. How could that matter?

Well, if you don't find the no branching rule plausible, you're in trouble as a body theorist. In fact, so what we see is, the body theory is in exactly the same problem, exactly the same situation, as the personality theory. Indeed, the fission example is a very nice case of how you could have splitting for the personality theory. Here, before the accident, was Shelly Kagan, somebody who had my beliefs, desires, memories, goals, and so forth. After the accident, we've got two people, Lefty and Righty, or two entities, Lefty and Righty, both of whom have Shelly Kagan's memories, beliefs, desires, goals, and so forth. Splitting the brain shows how you could, in fact, have splitting of personality. So the very same case raises the very same problem for both the body view and the personality view. And the only solution that I can see, at least the best solution that I can see, is to accept the no branching rule. If you don't like the no branching rule, it's not clear what your alternatives are. Or at least, it is clear what your alternatives are; it's not clear which alternative would be any better.

Now during all of this--problems for the personality theory, problems for the body view--during all of this, the soul theorist is having a field day. The soul theorist is saying, "Look you guys, you got into all this trouble with splitting and so forth and so on, and needing to add the no branching rule, silly and implausible as that seems, you got into all that trouble because of the problem of splitting because personalities can be split, bodies can be split. If only you had seen the light and stuck to the soul theory of personal identity, all these problems could be avoided." Now, as you know, I don't believe in souls. But forget that issue for the moment. Let's just ask the question, "Is it true that the soul theory--if only there were souls--is it true that the soul theory would at least have the following advantage? It avoids these problems of duplication and fission."

Well let's ask. What should a soul theorist say about the fission case? So here's the gruesome accident. My brain gets split apart. One part gets put into Jones' torso. One part gets put into Smith's torso. After the operation, Lefty wakes up thinking he's Shelly Kagan. Smith wakes up thinking he's Shelly Kagan. Lefty's got part of Shelly Kagan's brain. Smith's, or rather Righty's got part of Shelly Kagan's brain. What should the soul theorist say about the case of fission? Well, again, remember, the soul theory says the key to being the same person is having the soul. Why am I the person that was lecturing to you on Thursday? Because it's the very same soul animating my body, or what have you.

So, what does the soul theorist say about the fission case? I'm not quite sure, because we have to turn to a metaphysical question that we've touched upon before, namely, can souls split? After all, the problem that fission raises for the personality theory, in a nutshell, is that personalities can split, they can branch. The problem for the body view that fission raises, in a nutshell, is that bodies can split. They can branch. We need to ask about the metaphysics of the soul, can souls split? And I don't know the answer to that, of course. So let's consider both possibilities.

Possibility number one. Souls, just like bodies, just like personalities, can split. Suppose that's what happened. So, there was a single soul here, Shelly Kagan's soul, but in the middle of this gruesome operation, gruesome accident and followed by this amazing operation, Shelly Kagan's soul split. So there's one of the SK souls over here and there's one of the SK souls in the other case as well. Each one of Lefty and Righty has one of the pieces of the split Shelly Kagan soul

All right, so now we ask ourselves, "According to the soul theory, which one is Shelly Kagan?" Well, you--By this point, you can run through all the possibilities yourself, right? We could say, well, it's Lefty and not Righty. But there's nothing in the soul theory that supports that claim. They each have an equally good--however good it may be--they've got an equally good piece of the original Shelly Kagan soul. So there's no reason to say that Lefty is Shelly Kagan and Righty isn't. There's no good reason to say Righty is Shelly Kagan and Lefty isn't.!

Well, would it be better to say they're both Shelly Kagan, as long as you've got a piece of Shelly Kagan's soul, of the original soul, then you just are Shelly Kagan? In which case, Lefty and Righty are both Shelly Kagan, and Shelly Kagan is now bicoastal, one in California, one in Vermont, one part of him? That doesn't seem very satisfying.

What's the alternative? The alternative, it seems, for the soul theorist, is to say, neither of them is Shelly Kagan. Neither of them is Shelly Kagan, then Shelly Kagan died. But how can we say that if we accept the soul theory? They both have pieces of Shelly Kagan's soul. The soul split. Well, maybe what the soul theorist would have to do at this point is accept the--da-ta-da--the no branching rule. "Ah," says the soul theorist, "Follow the soul--unless the soul splits, in which case neither of them is Shelly Kagan." Well, the trouble is, we didn't find the no branching rule very plausible. It seemed counterintuitive.

But at this point, you begin to wonder, maybe we just need to learn to live with it. If the personality theory needs the no branching rule, and the body theory needs the no branching rule, and the soul theory needs the no branching rule, maybe we're just stuck with the no branching rule, whether or not we like it. And if we're stuck with it, then of course it's not an objection against any one of the theories that uses it. Well, this is all what we would say as soul theorists if we think souls can split.

But we need to consider the possibility that souls can't split. Maybe the soul theorist has an alternative available to it that--available to him that the other theories don't have. Suppose Shelly Kagan's soul cannot split. What does that mean? It means, when my brain gets split, my soul is going to end up in Lefty or in Righty, but not in both. If a soul can't split, you can't end up with pieces of the soul or the remnants of the soul in both. The soul is a unified simple thing.

Now, I don't actually know whether it's true that simple things can't split. Metaphysically, I'm not sure whether that's a possibility or not. But let's just suppose--look, Plato argued the soul was simple. He didn't actually convince me of that, but suppose we thought souls are simple, and we think simple things can't split. It would follow, then, that souls can't split.

Suppose we accept all that metaphysics. Then the question is just, which one is Shelly Kagan? Well, it depends which one ended up with Shelly Kagan's soul. We can't say, they both have a piece. One of them will have it, the other one won't. And you want to know which one's Shelly Kagan? The one that actually ends up with Shelly Kagan's soul. If Lefty ends up with Shelly Kagan's soul, then Lefty is Shelly Kagan and Righty is an imposter. He thinks he's Shelly Kagan, but he's not, because he doesn't have Shelly Kagan's soul. Lefty has it. If Righty's got Shelly Kagan's soul, then Righty is Shelly Kagan and Lefty is the imposter.

Now, looking at the situation from the outside, we might be unable to tell which one is really Shelly Kagan. Because we won't be able to tell, looking at it from the outside, which one really has Shelly Kagan's soul. Although it will be true, whichever one really does have Shelly Kagan's soul is Shelly Kagan. But we don't know which one that is.

Interestingly, and somewhat more surprisingly, looking at it from the inside, we won't be able to tell either. Lefty will say, "Give me a break. Of course I'm Shelly Kagan. Of course I've got Shelly Kagan's soul. Of course I'm the one." But Righty will also say, "Give me a break. Of course I'm Shelly Kagan. Of course I've got Shelly Kagan's soul. Of course I'm the one." If souls can't split, one of them is mistaken. But there's no way for them to know which one is the one that's deceived.

Now, that may not be a problem that you're unwilling to swallow. As we've seen, all the views here have their difficulties. Maybe that's the difficulty you're prepared to accept. What's the right answer in fission? It depends on who's got Shelly Kagan's soul. No way to tell. But still, that's the answer to the metaphysical question. Question?

Student: What happens if neither of these had Shelly Kagan's soul?

Professor Shelly Kagan: The question was, "What if neither of these have Shelly Kagan's soul?" Then they're both imposters. That's a little bit like the case we worried about when we started thinking about the soul view, right? What if last night God destroyed my soul and put in a new soul? Then Shelly Kagan died. If Shelly Kagan's soul does not migrate to Lefty or Righty, neither of them is Shelly Kagan, according to the soul theory. What happened to Shelly Kagan? Well, if the soul got destroyed, Shelly Kagan died. If the soul didn't get destroyed, maybe somebody else that we weren't even looking at is Shelly Kagan.

So as I say, the soul theory can at least give us an answer that avoids the no branching rule. If souls are simples and simples can't split, there's no possibility of having two things with a relevant soul. So we don't need to add, in this ad hoc fashion, the no branching rule. That's an advantage for the soul theory, if only we believed in souls. It is an advantage. But I need to point out that there's another disadvantage that the fission case raises for the soul theory.

So let's just suppose that metaphysically God tells us that it's Lefty that has Shelly Kagan's soul. Then of course it's Lefty that is Shelly Kagan. Righty is an imposter. Righty believes he's Shelly Kagan, he has all the memories of Shelly Kagan, all the desires of Shelly Kagan, but he's not Shelly Kagan because he doesn't have Shelly Kagan's soul. Lefty happens to have it. That's a nice answer to the problem of fission, but notice the problem it raises for the argument for believing in a soul in the first place.

Way back at the start of the semester when we asked, "Why believe in souls?" one important argument was, or really family of arguments was, you need to believe in souls in order to explain why bodies are animated, why people are rational, how they can have personalities, how they can be creative, and so forth. In order to explain consciousness and self-awareness. Whatever it was, fill in your favorite blank, fill in the blank in your favorite way. The claim was, you needed to believe in souls in order to explain all that.

But if that's right, what's going on in Righty's case? Righty is aware. Righty is conscious. Righty is creative. Righty has free will. Righty makes plans. Righty's got personality. Righty is rational. Righty's body is animated. According to the soul-theory argument for soul, rather, according to the argument for souls, you needed to believe in souls in order to explain how you could have a person. But now Righty's a person without a soul, because we just hypothesized, oh, Shelly Kagan's soul's up there. So at the very same moment that positing the nonsplitting of souls seems to solve the fission problem of duplication, it yanks the rug out from underneath the soul theorist by undermining one of the types of arguments for believing in the soul in the first place. After all, if Righty can be a person, admittedly not Shelly Kagan, but a person--conscious, creative, rational, so forth, aware--without a soul, then maybe the same thing is true for us, which is of course what the physicalist says.

Let me mention one other possibility, because it's quite intriguing. Suppose the soul theorist answers that last objection by saying, "Ain't ever going to happen." Yeah, it would be a problem for believing in souls if Righty could wake up without one. But since we stipulated that Shelly Kagan's soul is going to end up in Lefty, Righty is not going to wake up. Alternatively, it might have been that Righty woke up, but Lefty doesn't wake up, doesn't survive the operation. Suppose we did these sort of brain transfers all the time and the following thing always happened. Transfer the entire brain, the patient wakes up. Transfer one hemisphere, the patient wakes up. Transfer both hemispheres, one patient or the other wakes up, but never both. If that happened, we'd have a great new argument for the existence of a soul. What could possibly explain why either hemisphere of the brain would normally be enough, as long as we don't transfer both? When we transfer both, one hemisphere might work sometimes, sometimes the other hemisphere, but never both. What could possibly explain that? Souls could explain that. If souls can't split, it can only follow one half of the brain, and that's why we'll get somebody that's got one half, sometimes the other half, but never both halves.

So there's a kind of empirical argument for the existence of the soul if we found those kinds of results. Of course, that's a big "if." Please don't go away thinking that what I just said is, here's a new argument for the soul. We don't do brain transfers, let alone have a half-a-brain transfers. We don't have any experiments that suggest one half wakes up, but not the other half. All I'm saying is that if someday we found that, at that point, we'd have an argument for the soul.

Well again, let me put away the soul theory again. I was exploring it because it's interesting to think about its implication. But since I don't believe in souls, I want to choose between the body view and the personality view. Both of them, as we saw in the face of fission, needs to accept a no branching rule. If they're going to survive thinking about this case at all, we need to throw in a no branching rule. Whether or not you find the no branching rule hard to believe, if both views are stuck with it, well, then we're stuck with it. So let's try to choose between the personality theory with the no branching rule and the body theory with the no branching rule. Which of these should we accept? Which of these is the better theory of personal identity? Answer, "I'm not sure."

Over the course of my philosophical career, I have moved back and forth between them. There was certainly a long period of time in which I found the personality theory, that is, the personality theory with a no branching rule, to be the better and more plausible theory. And it certainly has any number of advocates on the contemporary philosophical scene. But at other times in my philosophical career, I have found the body theory, that is to say, the body theory with the no branching rule, to be the more plausible theory. And it is certainly the case that the body theory has its advocates among contemporary philosophers.

For what it's worth--and I don't actually think that what I'm about to say is worth all that much--I'm going to share with you my own pet belief. These days I'm inclined to go with the body theory. I'm inclined to think that the key to personal identity is having the same body, as long as there's no branching, as long as there's no splitting. But it's certainly open to you to decide that you think no, no, the personality theory is the stronger view. I can't settle the question. I don't have any more philosophical arguments up my sleeve on this issue. But I do have another point that's worth considering. Although I'm inclined to think that the body theory may be the best view about what's the key to personal identity, I'm also inclined to think it doesn't really matter.

 

We've been posing the following question. We've been asking, "What does it take for it to be true that I survive?" And it may be that what we should conclude is, whatever the best answer to that question is, it's not the question we should really have been thinking about. We weren't going to be in a position to see that until we went through all the stuff we've been going over for the last couple of weeks. But now that we're here, we're in a position perhaps to raise the question, should we be asking what it takes to survive? Or should we be asking about what matters in survival?

Now, in posing this question, I'm obviously presupposing that we can draw a distinction between the question, "Do I survive? Is somebody that exists in the future, whatever, me?" and the question, "What was it that I wanted, when I wanted to survive? What was it that mattered in ordinary survival?" And it might be that these things can actually come apart. To see this, suppose we start by thinking again about the soul view. Suppose there are souls. I don't believe in them, but let's imagine. Suppose there are souls. And suppose that souls are the key to personal identity. So somebody is me if they've got my soul. Or, to put it more straightforwardly, next week the person that's me is the person with my soul. I survive as long as there's somebody around with my soul. A hundred years from now, am I still around? Well, if my soul's still around, that's me. That's what the soul theory says. And suppose it's the truth.

Now, consider the following possibility. Suppose that people can be reincarnated. That is to say, at the death of their body, their soul takes over, animates, inhabits, gets connected to a new body that's being born. But, unlike the kind of reincarnation cases that get talked about in popular culture and various religions where, at least under the right circumstances, you can remember your prior lives, let's imagine that when the soul is reincarnated, it's scrubbed completely clean, no traces whatsoever of the earlier life. No way to retrieve it. No karmic similarities of personality or anything, just starts over like a blank slate. Like a blackboard that's been completely erased, we now have the very same blackboard, and now we start writing new things on it. Imagine that that's the way reincarnation worked.

So somebody asks you, "Will you still be around in 1,000 years?" The answer's going to be, yes, because my soul will be reincarnated. In 1,000 years there'll be somebody that has the very same soul that's animating my body right now. Of course, that soul won't remember being Shelly Kagan. It won't have any memories of its prior life. It won't be like Shelly Kagan in any way in terms of Shelly Kagan's desires or ambitions or goals or fears. It won't be that--We can see why that personality emerges through karmic cause and effect in any way that are a function of what I was like in my life. It'll be Shelly Kagan, because it's Shelly Kagan's soul, but with no overlap of personality, memories, anything.

Then I want to say, who cares? The fact that I will survive under those circumstances doesn't give me anything that matters to me. It's no comfort to me to be told I will survive, because after all, the soul is the key to personal identity, if there's no similar personality, no memories, no beliefs, no retrievable memories of past lives. Then who cares that it's me?

If you can feel the force of that thought, then you're seeing how the question "Will I survive?" can be separated out from the question "What matters?" What do we care about? Bare survival of my soul, even though that is the key to personal identity--if it is--bare survival of my soul doesn't give me what I want.

It's no more comforting or satisfying than if you said, "You know this knucklebone? After you die, we're going to do knucklebone surgery and implant that knucklebone in somebody else's body. And that knucklebone is going to survive." And I say, "Oh, that's very interesting that that knucklebone will be around 100 or 1,000 years from now. But who cares?" And if the knucklebone theory of personal identity gets proposed and somebody said, "Oh, yes, but you see, that person now with that knucklebone will be you, because the key to personal identity is having the very same knucklebone." I say, "All right, so it's me. Who cares?" Bare knucklebone survival does not give me what matters.

Now, the knucklebone theory of personal identity is a very stupid theory. In contrast, the soul theory of personal survival is not a stupid theory. But for all that, it doesn't give me what I want. When you think about the possibility of bare survival of the scrubbed, clean, erased soul, you see that survival wasn't really everything you wanted. What you wanted--at least what I want, I invite you to ask yourself whether you want the same thing--what I want is not just survival, but survival with the same personality. So even if the soul theory is the correct theory of personality, it's not enough to give me what matters. What matters isn't just survival. It's survival with the same personality.

Let's consider the body view. Suppose that the body theory of personal identity is correct. And to be me, there's got to be somebody there that's got my body. Let's suppose the brain version of the theory is the best version. And so next year, there's going to be somebody that's got my brain. But let's imagine that the brain has been scrubbed clean. All memory traces have been completely erased. We're talking complete irreversible amnesia, complete erasure of the brain's hard drive. No traces of desires and memories and intentions and beliefs to eventually be recovered if only we have the right surgery, or procedure, or psychotherapy, or what have you. It's gone.

Now, that thing that wakes up after this complete irreversible amnesia will no doubt eventually develop a personality, a set of beliefs, memories. Nobody knows who it is, so they call it, they find it wandering on the streets. They call it John Doe. John Doe will eventually have a bunch of beliefs about how the world works, make some plans, get some memories. According to the body theory, that's me. And if the body theory is correct, well by golly, it is me. And all I can say in response to that is, it's me, but who cares? So what? I'm not comforted by the thought that I will still be around 50 years from now, if the thing that's me doesn't have my personality.

Mere bodily survival isn't enough to give me what I want. I want more than mere bodily survival. I want to survive with the same personality. So even if the body theory of personal identity is the right theory, what I want to say in response to that is, "So what?" If the really crucial question is not "Do I survive," but "Do I have what I wanted when I wanted to survive?" the answer is the body theory doesn't give it. I don't just want to survive. I want to survive with the same personality.

Should we conclude, therefore, that the key to the important question--namely, "What matters?"--the answer to that question, should we conclude, is, same personality? That's a question we'll have to take up next time.