Death

PHIL 176 - Lecture 11 - Personal Identity, Part II: The Body Theory and the Personality Theory

Chapter 1. Review of Soul Theory [00:00:00]

Professor Shelly Kagan: Last time, we turned to the question of what the metaphysical key to personal identity might be. What makes it be the case that one person, some person that exists in the future, is the same person as me. The first approach to this that we considered was the soul theory of personal identity: the key to being the same person is having the same soul. Same soul, same person. Different soul, different person. And the difficulty with that approach, even if we bracket the question whether or not there are souls, the difficulty with that approach was that it seems as though the soul could constantly be changing while the personality, as we might call it, stays the same. I have the same beliefs, memories, desires, goals, preferences and so forth. But the soul underneath it all keeps being swapped every five minutes. If the soul theory of personal identity were right, that would not be me. I would be — Every five minutes that person would die and we'd have a new person, despite having the same personality.

Most of us find that a rather difficult thing to believe, that the person could be constantly changing in this way, without having any way at all to tell. And if we're not willing to accept that implication, it seems as though we need to reject "the soul theory of personal identity." Now, I use this cumbersome phrase because, of course, I'm not here talking about rejecting the existence of souls. What I'm considering right now is the question whether sameness of soul is the key to being the same person. And this is a — There's a logical distinction here that's worth drawing. Even if you believe in souls, you don't have to say that having the very same soul is the key to being the very same person. And trivially, of course, if you don't believe in souls, if you don't believe that souls exist, that you certainly can't appeal to the existence of souls, the continuity of soul, the sameness of soul, as the key to personal identity.

But we might then ask, "Well what's the alternative?" Now, the natural alternative is to say, "The key to being the same person is not the sameness of the soul, whether or not it exists, but rather having the very same body." And again, although I'm not going to go on and on about this point, it's worth noticing that even if you do believe that souls exist, nothing stops you from accepting the body theory of personal identity. Nothing rules out the possibility that having the very same body is the key to being the very same person over time. Even if you believe in souls, you can accept the body theory. And it certainly looks as though if you don't believe in souls, you have to accept the body theory of personal identity. Now, as it turns out, that appearance is deceptive. There are still other alternatives open to the physicalist, but let's come to that other alternative later.

Chapter 2. The Body Theory of Personal Identity [00:03:07]

Let's take a few minutes and consider the nature of the body theory, the body theory of personal identity. On this theory, of course, the secret to being the same person is having the same body. So when we ask, well you remember last lecture I was talking about how there'd be somebody here lecturing to you, philosophy, on Tuesday. Well, here somebody is. Is that the same person? Is the person who's lecturing to you now the same person as the person who was lecturing to you before? According to the body theory, the answer is — turns on the question, "Well, is this the same body as the lump of flesh and bone that was here last week?" If it is — and by the by it is — if it is, then it's the same person. So am I the person who was lecturing to you last week? Yes, I am, because it's the very same body. That's what the body theory says.

And unlike souls, where it's all rather mysterious how you could tell whether soul swapping was taking place or not, it's not all that mysterious how we check out to see whether the same body's been around. Even though you didn't do it, you could have snuck into my house, watched my body go to sleep, get up in the morning, followed the body around over the course of the day, see it go to sleep again. You could have tracked that body through space and time and said, "Hey look. It's the very same body." In the same way that we are able to track in principle cars, our earlier example, and talk about yeah, it's the same hunk of metal and wire and rubber and plastic. This is the same hunk, same body. All right, same body, same person. That's the body theory of personal identity.

Now, if we accept the body theory, then of course if we turn to the question, "Could I survive my death?" Could I survive the death of my body?" at first glance, it looks as though the answer's going to have to be, "Well, of course not." Because when my body dies, then, oh eventually the body begins to decay. It decomposes, turns into molecules which get absorbed into the soil or what have you. This may take years or decades or even centuries, but my body no longer exists after death of my body. And so how could I survive the death of my body, if for me to survive the death of my body, there's got to be somebody who's me, and if being me requires it being the same body, my body would have to still be around, but it's not. That's what it looks like at first glance.

But at second glance we see that there's at least a logical possibility of surviving the death of my body. All it takes is for my body to be put back together. Bodily resurrection. Now I'm not going to here pursue the question of, "Do we believe bodily resurrection occurs or will occur?" I'll note that there have been religious traditions that have taught and believed in this possibility. In particular, it's probably worth mentioning that early Christians believed in something like the body theory of personal identity and believed in bodily resurrection that would happen on Judgment Day. We can certainly understand the possibility that God would perform a miracle, put the molecules back together, turn the body back on. Same body, same person, come Judgment Day. That's the possibility. So it's at least worth emphasizing the fact that even if we don't believe in souls, we could still believe in the possibility of surviving one's death, the death of one's body, if we're willing to believe in bodily resurrection. Well, that's how it looks.

Now let's take a harder look. Talking that way assumes that when you put the body back together, when God puts the body back together on Judgment Day, that that's still my body. Is that right? I'm inclined to think it is right. If God gathers up all the various molecules that had composed my body, reassembles them in the right order, putting this calcium molecule next to that hydrogen molecule and so forth and so on, reassembles them in the right way — obviously if what He makes out of my body's molecules is a Cadillac, then that's not my body — but if He puts them together in the right way, that seems like it should be my body.

So here's an analogy to give you a sense of what's going on. Suppose I take my watch to the jeweler because it stopped working. And in order to clean it and fix it, repair it, what the jeweler does is he takes it apart. He takes the rust off of the gears, if there are still gears in watches. Imagine it's an old stop watch. And he cleans all the pieces and buffs them and polishes them and then reassembles the whole thing. And a week later, I come back and ask, "Where's my watch?" And he hands it to me. Well, all well and good.

Now imagine some metaphysician saying, "Wait a minute, buster. Not so quick. That's not my watch. Admittedly, it's composed of all the very same pieces that made up my watch. Admittedly, all these pieces are in the very same order as my watch, but still that's not my watch." On the contrary, it seems to me the right thing to say about that example is, "No, that is my watch." My watch was disassembled for a period of time. Perhaps we should say my watch didn't exist during that period of time. But it got put back together. Now that's my watch. If that's the right thing to say about the watch — and it does seem to me to be the right thing to say about the watch — then God could presumably do the same thing on Judgment Day. He could take our molecules, which had been scattered, put them back together and say, "Ha! That's your body." And if the body theory of personal identity is right, well, that would be me. So it seems to me.

But there's a different example that we have to worry about as well, which argues against this proposal that the body could decompose and then be recomposed. This is an example that's due to Peter van Inwagen. He's a contemporary metaphysician, teaches at Notre Dame. Suppose that my son builds a tower out of wooden blocks. We have a set of wooden blocks at home. Suppose that he builds some elaborate tower. It's very impressive. And he says, "Please show it to mom when she comes home." And he goes to bed. And I'm very good. I'm cleaning up the house after he goes to bed and oops, I knock over the tower. I say, "Oh my god, he's going to be so angry. I promised him I'd be careful." So what I do is I take the blocks and I put them back together, building a tower in the very same shape and the very same structure, the very same order as the tower that my son had built. And in fact I'm so careful — perhaps the blocks are numbered — I'm so careful that every block is in exactly the same position as in the case where my son built it.

All right, I rebuild or I build this tower and my wife comes home and I say, "Look what our son built. This is the tower that our son built." Ah, that doesn't sound right. That's not the tower that our son built. That's a tower that I built. This is a duplicate tower. Sure, if my son were to wake up and I didn't tell him, he wouldn't know that it was a duplicate. But when you take a wooden block tower apart and then put the pieces back together, piece for piece, duplicate, you don't have the very same tower that you started out with. That's what van Inwagen says and, I've got to admit, sounds right to me. If I were to point to that tower and say, "Ari built that," I'd be saying something false. "That's the very same tower that Ari built." No, I'd be saying something false.

So van Inwagen concludes, if you have an object and you take it apart and then put it all back together again, you don't have the very same object that you started out with. So even if Judgment Day were to come, and God were to reassemble the molecules and resurrect the body, it's not the very same body that you started out with. And if having the very same body is the key to personal identity, it's not the same person. Come Judgment Day, we've got a duplicate of me, but we don't have me. That's what van Inwagen would say, if that's the way bodily resurrection would work.

I don't know, theology aside, I don't know what to say about the metaphysical questions. When I think about the tower case, I do find myself inclined to say, with van Inwagen, that's not the tower my son built. But when I think about the watch case, I find myself saying that is the very same watch. Now, all I can do is invite you to think about these two cases and ask yourself, what should we say here? Of course, for those people who think it really is the same tower, no problem. Then we say, the watch and the tower, in both cases, it's the very same object when it's reassembled. Reassemble the body, that'll be the very same body as well. For those people who say, "Yeah, van Inwagen was right about the tower, and the same thing would be true about the watch. The reassembled watch isn't the very same watch," then we have to say bodily resurrection would not be the very same body. So that wouldn't be me waking up on Judgment Day.

The alternative is to try to find some relevant difference between the watch case and the tower case. Something that allows us to say that "well, when you reassemble the watch it is the same watch. When you reassemble the tower, it's not the same tower. Here's the explanation of why those two things work differently in the reassembly cases." And then of course, we'd have to further investigate whether when you reassemble a body, is it more like the watch case or is it more like the tower case?

I just have to confess, I don't know what the best thing to say about these cases is. I find myself inclined to think reassembled watch, same watch. Reassembled tower, not same tower. Maybe there's a difference there. I don't have a good theory as to what the difference is. Since I don't have a good theory as to what the difference is, I'm not in a good position to decide whether a reassembled body would be the same body or a different body. I don't know. So there's metaphysical work to be done here by anybody who's at least interested in getting this theory of identity worked out properly.

Still, at least the possibility that we could work this out is still there. So I suppose there's still at least the possibility that bodily resurrection would be coherent in such a way that it would still be the same body. So if we accept the body theory, could there be life after death? Could there be survival of the death of my body? Seems like, as far as I can tell, it's still a possibility, although there's some puzzles here that I don't know how to see my way through. Mind you, that's not to say that I myself do believe that there will be a Judgment Day, and on that day God will reassemble the bodies. But it at least seems like a coherent possibility.

Let's refine the body view. I've been suggesting that the key here, the idea of whether it's the same person or not, is whether it's the same body. But of course as we know in thinking about familiar objects, we don't need to have every single piece of an object, of an entity, stay the same to have the same thing. So I think I previously talked about the steering wheel in my car. Every time I drive the steering wheel in my car, I rub off some atoms. But that's okay. It's still the very same physical object. The steering wheel is — Having the same steering wheel is compatible with changing of a few pieces. The same thing is true for bodies, right? You get sunburned, your skin peels, you've lost some atoms in your body. It doesn't really matter. It's still the very same body. So if body is the key to personal identity, we don't have to worry about the fact that we're constantly gaining and losing atoms. Yes, question?

Student: What about someone who loses a huge amount of weight?

Professor Shelly Kagan: Good. The question was, "What about somebody who loses a huge amount of weight?" They feel different. People treat them different. What about that case? Well, I think if we're doing metaphysics, as opposed to psychology — Psychologically, we understand why losing weight might make a real difference as to how you feel about yourself. And we might even say, loosely, it's as though she's a whole new person. But strictly speaking, we don't think it is literally a whole new person. It's not as though we say, "Poor Linda died when she entered the spa. Or a week into the spa when she dropped those 50 pounds. Somebody else who remembers all of Linda's childhood, some imitator came along." We don't say "different person." We say "same person, lost a lot of weight."

Now that's not a problem for the body view, because on the body view, the question is, is it the same body? And what we want to say is, of course, look, just like it's still your body even if you break your arm. Even though — It's still your body after you've eaten dinner, and so now some molecules have been absorbed into your body that weren't there before. It's still your body after you lose some molecules, even a lot of molecules. There can be changes in your body that are compatible with it still being the same body. Now, we might worry about the — Which changes? Are all the changes, it's certainly not as though any change will do. I mean, suppose what happens is Linda goes to bed and what we do in the middle of the night is we take away that body and put some new body there. Well that 100% change, that's clearly too much. Change of some small percentage, from eating, not a problem. Change from a somewhat larger percentage of losing a fair bit of weight doesn't seem to be a problem.

So which changes in bodies make for a different body and which changes in body make for the same body? And in particular, how should we run that if we're thinking about the body as the key to personal identity? I think if we have that question in front of our minds, we're going to want to say not all parts of the body are equally important. You lose a fair bit of weight, some fat from your gut, not a problem.

Here's one of my favorite examples. In the Star Wars movies, Darth Vader whips out his light saber and slashes off the hand of Luke Skywalker. "Luke, I am your father." "No!" Then the hand goes, right? The very next scene — this has always amazed me — the very next scene, Luke's got an artificial hand that's been attached to his body and they never even mention it again. No one says, "Oh, poor Luke. He died when Darth Vader cut off the hand."

It seems pretty clear that not all parts of the body matter. You can lose a hand and still survive. Same body, except now without a hand. Suppose Darth Vader had aimed a little higher and cut off Luke's entire arm. It would still be Luke. It would still be Luke's body. Suppose, even worse, Darth Vader slices off both arms and both legs. It would still be Luke. It would still be Luke's body, though now without arms and legs.

What part of the body, if any, is essential? Well here's a proposal. It seems to me we'd say something rather different if what happened was that what got destroyed was Luke's brain. Suppose that Darth Vader uses the force — the dark side of the force of course — Darth Vader uses the dark side of the force to destroy, to turn into pea soup, Luke Skywalker's brain. Now I think we might want to say, "Well look, no more Luke." And if what happens is they drag out some replacement brain, it's still not Luke.

At least, that's a possible version of the body view. According to this version, which I take to be the most promising, the best version of the body view, the crucial question in thinking about personal identity is whether it's the same body — but not all parts of the body matter equally. The most important part of the body is the brain. Well, why the brain? No surprise there, because of course the brain is the part, we now know, the brain is the part of the body that is the house of your personality, your beliefs, your desires, your fears, your ambitions, your goals, your memories. That's all housed in the brain. And so that's the part of the brain that's the key part of the body for the purpose of personal identity.

That's what I'm inclined to think is the best version of the body view. We find examples of this thought, that the brain is the key, in odd places. So let me actually share one with you. This was something from the Internet that my brother sent to me some years ago. It purports to be from a transcript from an actual trial in which a lawyer's cross examining the doctor. And you'll see. I don't actually know whether it's true or not, whether it's just somebody made it up. But it purports to be true.

Q: Doctor, before you performed the autopsy, did you check for a pulse?
A: No.
Q: Did you check for blood pressure?
A: No.
Q: Did you check for breathing?
A: No.
Q: So then it is possible that the patient was alive when you began the autopsy?
A: No.
Q: How can you be so sure, doctor?
A: Because his brain was sitting on my desk in a jar.
Q: But could the patient have still been alive nevertheless?
A: It is possible that he could have been alive and practicing law somewhere.

The point — The reason that this is funny, other than of course the obvious moral, which is that lawyers are morons, is that of course. Why is it so clear the lawyer's got to be a moron? Because of course we think, look, lose a hand, the guy could still be alive. Lose an arm, lose a leg. Lose the brain, he's not alive. So again this is, this is hardly philosophical proof, but it shows that we're drawn to the thought that the key part of the body is the brain.

Chapter 3. Equating the Brain with the Identity – Implications of the Body Theory [00:25:47]

Now, think about what the implication of holding that view. Suppose we adopt that version of the body view. If I get a liver transplant, so here I am and we take out my liver and we put Jones' liver inside. I've gotten a liver transplant. It's still me. Suppose we rip out my heart and put Jones' heart in here. I've gotten a heart transplant. It's still me. Suppose we rip out my lungs and put in Jones' lungs. I've gotten a lung transplant. It's still me. Suppose we rip out my brain, put in Jones' brain. Have I gotten a brain transplant? No. What's happened is that Jones has gotten a body transplant. Or, as we might put it, a torso transplant. If we accept this version of the body theory, we say the crucial part of the body for personal identity is not sameness of torso. The crucial part of the body is sameness of brain. Just like "follow the soul" was the answer if we believe in the soul theory of personal identity, if we believe in the brain version of the body theory of personal identity, same person or not? Follow the brain. Same brain, same person. Different brain, different person.

As I've now been saying several times, I think that's the best version of the body view, although not all body theorists believe that. As you know from reading your Perry, the assigned reading, his Dialogue on Personal Identity and Immortality, the heroine of that story, Gertrude — Gertrude actually thinks the key part of the body is the torso. Follow the torso, follow the person. That's what she thinks. I'm inclined to say, no. In those moods, when I accept the body theory, I'm inclined to think, no, follow the brain. Gertrude would presumably say you get a brain transplant, you got a brain transplant, because it's the same torso. I want to say, as a fan of the brain theory, you get a brain transplant, what's really happened is somebody else has gotten a torso transplant. Follow the brain.

How much of the brain? Do we need all of the brain? Well, just like we didn't have to follow the parts of the body that aren't essential for housing the personality, we might ask ourselves, "Do we need all of the brain to house the personality?"

Research suggests that there's a fair bit of redundancy in the brain. You can lose portions of the brain and still have a perfectly functioning, P-functioning person. Some of you may know that there have been experiments in which, for one reason or the other, the two halves of the brain have been separated. And you often end up there with, well, something closer to two persons being housed within one skull, because they can often still communicate in various ways. We don't quite get that. I gather that the best research suggests we don't really have complete redundancy with hemispheres.

But suppose that we did. Let's be science-fictiony. Suppose that, as a kind of backup security, what evolution has done is produced so much redundancy in the brain that either half of the brain would suffice. All right, so think about our brain transplant example. So there's an accident with Jones and Smith. Jones' torso gets destroyed. His brain is fine. Smith's brain has gotten destroyed. His torso is fine. We take Jones' brain; we put it in Smith's torso. We hook up all the wires, as it were. The thing wakes up. Who is that? Jones' brain, Smith's torso. Follow the brain. That's Jones that woke up.

Version two. Horrible accident. Jones' torso has been destroyed and the left half of his brain has been destroyed. But the right half of his brain is still there. Smith's torso is fine, but his entire brain has been destroyed. We take the right half of Jones' brain, put it into Smith's torso, hook up all the wires the right way, the thing wakes up. Who is it? It's Jones. Follow the brain, and more particularly, follow however much of the brain it takes to have enough of the brain there to still give you the memories, beliefs, desires, and so forth and so on. If it were true — it probably isn't true, but if it were true — that half of the brain was enough, then half the brain would be enough. That would be Jones that woke up. Question?

Student: [inaudible]

Professor Shelly Kagan: Great. The question was, "On this theory, what do we say about the case where we take the two halves of Jones' brain, split them, put them in two different torsos. They both wake up. Would they both be Jones?" That's a wonderful question. It's a wonderful case to think about and, indeed, I am going to come back to it. But I just want to bracket it for the time being. But it's a great question to keep in mind as you think about the plausibility of the body theory.

Chapter 4. Physicalists: Personality as the Key to Personal Identity [00:32:35]

All right, so I'm inclined to think that the best version of the body theory has to do with following the brain. So one thing that a physicalist, who does not believe in souls, one thing that a physicalist could say is, "What's the key to personal identity? The body. Sameness of body." And then I'm inclined to think the best version of the body view is the brain view. So that's something that a physicalist can say. And for that matter, it's something that a soul, somebody who believes in souls, could say as well: even though there are souls, that may not be the key to personal identity. Maybe sameness of body is the key to personal identity.

That's something a physicalist or dualist can say. But, and this is not — to make good on a promissory note I offered earlier, it's not the only view available to physicalists or, for that matter, dualists. Even if there are no souls, we don't have to say that the key to personal identity is the sameness of the body. We could instead say the key to personal identity is the sameness of the personality.

After all, go back to the Lockean worries about the soul theory of personal identity. It seemed very hard to believe that it isn't the same person when the memories and beliefs and desires and goals and ambitions and fears are all the same, even if a soul is constantly changing. It seems as though we wanted to say same person. Why? Roughly speaking, because it's the same personality. And with the body view, when I started arguing a few moments ago that the best version of the body view was the brain view, why did that seem plausible? Why didn't we say that Luke died when he lost his wrist? Because the brain, after all, was the part of the body that houses the personality. Enough of the brain was good enough, I said. What counts as good enough? Enough to keep the personality.

Well, if what we think is really important here is the personality, why don't we just say the key to personal identity is the personality? Let's just say it's me, provided that there's somebody who's got the same set of beliefs, desires, goals, memories, ambitions, fears. To coin a word, the same "personality." So the secret to personal identity on this new proposal isn't sameness of body, it's sameness of personality.

Now, it's important to bear in mind that this view is perfectly compatible with being a physicalist. After all, we're not saying that in order to have personalities you need to have something nonphysical. As physicalists, we can still say that the basis of personality is that there are bodies that are functioning in certain ways. But for all that, the key to the same person could have to do with the personality rather than the sameness of bodies. Of course, normally the way you get the same personality is by having the same body. Still, if we ask, "What's doing the metaphysical work here? What's the key to being the same person?" we can say sameness of body gave us the same personality, but it was sameness of personality that made it be the very same person.

Could there be some way to get sameness of personality while not having sameness of body? Maybe. Suppose that we had some disease. The doctor tells me the horrible news that I'm going to have some disease that's going to eventually turn my brain into pea soup. But luckily, just before it does it, they can take all of my personality and put it into an artificial replacement brain. So there'll be — just like you can have artificial hearts, artificial livers, you can have artificial brains, which will get imprinted with the same personality. Same memory, same beliefs, same desires, same fears, same goals. We obviously can't do that. This is a science fiction story. But at least it allows you to see how the body and the personality could come apart. And so we could have same personality without literally the same brain. If personality is the key to personal identity, that would still be me. Hold off again for a few minutes, at least, on the question, "So what should we believe here, the body, the personality view?" Let's try to refine the personality theory.

So again, the point I was just emphasizing was even if we accept the personality theory, this doesn't threaten our being physicalists. We can still say the reason that we've got the same personality in the normal case, is there's some physical explanation of what houses the personality. But for all that, the key to personal identity is same personality. Notice, by the way, that somebody who believes in souls could also accept the personality theory of personal identity. Locke believed in souls. He just didn't think they were the key to personal identity. So you might think, "Oh no. The physicalist is wrong when the physicalist says that personality — memory, belief, consciousness, what have you — is housed or based in the body. It's based in an immaterial soul." Dualists could say that. And yet, for all that, the dualist could consistently say, "Still, same soul is not the key to personal identity. Same personality is the key to personal identity. If God replaces my soul every 10 minutes, as long as He does it in such a way as to imprint the very same personality on the soul, it doesn't matter any more than it didn't matter whether or not some of my body parts were changing." So the personality theory of personal identity can be accepted by physicalists and it can be accepted by dualists.

So, just to keep score, right now we've got three basic theories of personal identity on the table. The soul theory, the key to personal identity is the same soul. The body theory, the key to personal identity is the same body. Where the best version, I think, is the brain version of the body theory. And the personality theory, the key to personal identity is having the very same personality.

Well again, we've got to be careful about refining this. Just like we all agreed, I suppose, that you can have the very same body, even though some of the parts come and go, atoms get added, other atoms get knocked off. We can say, we'd better say, that you can have the very same personality even if some of the elements in your personality change.

After all, we defined the personality in terms of it being a set of beliefs and memories and desires and goals and fears and so forth. But those things are constantly changing. I have all sorts of memories now that I didn't have when I was 10. I have memories of getting married, for example. I wasn't married when I was 10. So does the personality theorist have to say, "Uh-oh, different personality. That kid no longer exists. That person died, got married and the memories died." If we say that, we have very, very short lives. Because after all, right now I've got some memories that I didn't have two hours ago. I have some memories I didn't have 20 minutes ago. If every time you got a new memory you had a new personality and the personality theory said having the very same personality was the key to survival, then none of us survive more than a few seconds.

Well, the answer presumably is going to be that the best version of the personality theory doesn't require item for item having the very same beliefs, memories, desires, and so forth. But instead requires enough gradual overlap.

Your personality can change and evolve over time. So here I am as a 10 year old child. I've got certain desires, certain memories. As the year goes by, I get some new memories. I lose some of my goals. I no longer — When I was 10, when I grew up I wanted to be a trash collector. That was my first chosen profession. At some point I gave up that desire. I didn't want to be a trash collector anymore. I wanted to be, I kid you not, I wanted to be a logician when I was a teenager. I wanted to study symbolic logic. So at a certain point I gave that up. So my memories, my desires were changing, but they all changed gradually. I lost some old memories. I don't remember everything I knew or remembered when I was 10. When I was 10, I had pretty vivid memories of kindergarten. Now I have very sketchy memories of kindergarten. Still, it wasn't abrupt. It was gradual. There was this slow evolution of the personality. And so when the personality theorist says the key to personal identity is the same personality, they don't' mean literally the very same set of beliefs and desires. They mean, rather, the same slowly evolving personality.

Here's an analogy. Suppose I had a rope that stretched from that end of the room all the way across to this end of the room. Very same rope at that end as this end. What makes up a rope? Well as you know, ropes are basically bundles of fibers, very thin fibers that have been woven together in a certain way. But the interesting thing is the fibers themselves aren't actually all that long. They might be a couple of inches or at most a foot or so. And so no single fiber stretches all the way across the room. Or even if some fibers did, most of the fibers don't. Does that force us to say, "Ah, so it's not the very same rope at the end as at the beginning"? No. We don't have to say that at all. What we want to say is, "It's the same rope as long as there's this pattern of overlapping fibers." Certain fibers end, but most of the fibers are continuing. Some new fibers get introduced. They continue for a while. Eventually maybe those fibers end, but some new fibers have been introduced in the meantime. As long as it's not abrupt. Imagine I take my scissors and cut out a foot in the middle. Then we'd say there isn't the right kind of pattern of overlap and continuity. Now we really do have two ropes — one rope here, one rope there. But if, in contrast, there is the right kind of pattern of overlap and continuity, same rope, even though, even if no single fiber makes it all the way across.

Something analogous needs to be said by the personality theorist. Even if I have few or no memories identical to the ones that I had when I was 10, that's okay. We can still say it's the same personality, the same evolving personality, so long as there's a pattern of overlap and continuity. New memories get added, some memories get lost. New goals get added, some goals get lost. New beliefs get added, some beliefs get lost. There might be few beliefs, desires, goals that made it all the way through. But as long as there's the right kind of overlap and continuity, same personality.

Chapter 5. Soul, Body, and Personality – Is There a Correct View? Assessment by Torture [00:46:39]

All right, so what have we got? Three views — soul view, body view, personality view. Three rival theories about the key to personal identity. Now, which of these is right? Well, I don't myself believe in souls, it's hardly going to surprise you to learn that I don't think the soul theory of personal identity is right. For me, the choice boils down to the choice between the body theory of personal identity and the personality theory of personal identity. Of course, in real life, they go hand in hand. In ordinary cases at least, same body, same personality. Both theories are going to say it's the very same person. And if you believe in souls, you are likely to think, same soul as well. In ordinary cases, you have the same soul, same body, same personality, same person.

To think about which one of these is the key to personal identity, we need to think about cases, maybe somewhat fantastical, science-fictiony, in which they come apart. Cases in which bodies and personalities go their own ways, as it were.

So that's what I'm going to do. I'm going to tell you a story in which your body ends up one place and your personality ends up someplace else. And I'm going to invite you to think about which of these two resulting end products is me. If you could figure out which one's you, that would tell you whether you think the body theory is the right theory or the personality theory is the right theory.

Now, what's going to be our guide? I'm going to, rather gruesomely — not in real life, a science fiction story — I'm going to torture one of the two end products. I'm going to ask you, "Which one do you want to be tortured?" Or to put the point more properly, which one do you want to not be tortured? Because I'm going to assume, I'm going to take it, that it's important to you that you not be tortured. So by seeing who you want to keep safe, this will help you see which one you think is you.

Of course, I've got to be sure that you're thinking about this in the right way. Like some of you are probably good, moral individuals and you don't want anybody to be tortured. I say, "Ah, I'm about to torture Linda over there." You say, "No, no. Don't torture Linda." Still, if I were to say to you, "I'm about to torture you." You'd say, "No, no! Don't torture me!" and there'd be some extra little something when you said that, right? So I want to invite you to keep that extra little something in mind when we tell the stories, which we won't get to until next time, when we tell the stories next time, and I say, "Okay, who do you want to be tortured, this person or that person?" The question is, from that special egoistic perspective that we're all familiar with, which is the one you really care about? That's going to be our guide to deciding what's the key to personal identity. But to hear the stories, you've got to come back next lecture.

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