▶︎ 0:01 In the last lecture, we talked about the question of personal identity over time as it's been investigated by metaphysicians in recent decades. And we also talked about what's arguably the most widely held answer to that question, which is the psychological approach or psychological continuity theory of personal identity. But for all its popularity, this theory hasn't been without some challenges, and it's had plenty of critics.
▶︎ 0:26 In this lecture, I'm going to talk about some puzzles and challenges for this account of personal identity, as well as some of the answers and responses that are given to those puzzles, and also show how it leads to a resurgence in some sense of the biological or bodily criterion, and I'll talk about what that's looked like in the last twenty, thirty years.
▶︎ 0:48 But I'm going to begin by talking about some objections that are raised to the psychological continuity theory by psychological continuity theorists themselves. They raise these objections because they're trying to think hard about their view and determine where its weak points are and whether they can be answered. And so they've come up with some pretty serious challenges.
▶︎ 1:10 We saw last time that psychological continuity theorists use hypothetical science fiction-y cases to defend their views, cases where people swap bodies, brains are transplanted, brain state transfer devices, and so on. But the use of these cases, as important as it's been for them, is something of a double-edged sword, because once you start allowing people to make up science fiction cases and see how people respond to them, it's pretty easy to generate more complicated cases, cases that ultimately raise a lot of problems for the psychological account.
▶︎ 1:44 I'm going to talk about versions of two of these kinds of hypothetical cases, and these were raised by Derek Parfit, who offered an extremely important and influential version of the psychological approach in a 1984 book called Reasons and Persons. And he's really responsible for the versions of the cases that we mostly talk about today. The cases were out there in the literature. People were writing about different problems and strengths of the psychological approach.
▶︎ 2:14 And what Derek Parfit did is collected all of these cases and all of these arguments and presented them in a very systematic way. He probed and dug a little deeper into them and what they implied and presupposed, and he drew some really astonishing conclusions from them that have been very important. So Parfit offers two cases that I'm gonna talk about.
▶︎ 2:37 The first is actually a pair of cases. It's called teletransportation in the branch line case, and the second is what's called the fission case. Teletransportation is a Star Trek-like form of transport to distant planets. He imagines it's a typical sci-fi example that's very much along the lines of the ones that I talked about in the previous lecture. It's in the future, if you need to go do business on Mars, for instance, you can either take the old-fashioned spaceship route, which is very, very long, or if you need to get there quickly, you use the teletransporter.
▶︎ 3:15 In the teletransporter, you walk into a booth on Earth. A machine takes a scan of the exact position of every molecule in your brain and body. In so doing, it incinerates that body, but it has the information. It beams it to Mars at the speed of light, and then very quickly, a molecule for molecule replica of the person who walked into the booth on Earth is created on Mars.
▶︎ 3:39 And it's presupposed that whatever mental states are and whatever consciousness and psychological life is here, it's generated in some way or caused in some way or closely related to what goes on in the brain. It's just presupposed in the case that if you make a molecule for molecule replica of the brain and the whole nervous system in the body, you'll have exact duplication of the psychological life as well. The way that it's presupposed in the case from the point of view of the person, they walk into the booth, they push a button, they seem to lose consciousness for a few seconds, sort of like if you had fallen asleep on a plane flight or something, then they wake up, they're on Mars, someone wakes up on Mars, thinks, "Yeah, that really was easy, I'm glad I didn't take the spaceship," walks out, does their business, concludes it, buys the souvenirs, gets in the teleporter on Mars, pushes the button. Someone comes out on Earth saying, "That was really quick and easy. I better go home and bring these souvenirs to the family."
▶︎ 4:38 So from the point of view of the person traveling, according to Parfit, it's just like taking a trip where you maybe fall asleep on the trip. You walk into the booth, you go to Mars, you come back, you go home. From the point of view of the people at home, it seems like what happened is that their loved one walked into the booth, went on a business trip, and came home. This is just the kind of case we've already talked about, and Parfit expects that most people will think that this is just a way to travel to Mars and back. But he also recognizes that some people won't think that,
▶︎ 5:14 That this is not going to be a universal intuition about this case. He thinks that some people will say this is not a way to travel to Mars. This is a way to get incinerated in a booth and have a replica created, and then somebody on Mars lives on Mars for a few days or weeks or whatever, gets incinerated, and a replica is built again. This is a form of death. It's not a form of travel. And he says that explanation, if you think that personal identity consists in psychological continuity, requires some explanation, but he wants to probe it further and see what's going on for those people who are worried. He wants to bring out the worry a little more.
▶︎ 5:55 So he imagines a second case, which he calls the branch line case. And in the branch line case, person walks into the booth after many years of traveling this way, pushes the button, and nothing happens. And so he comes out and says it's not working, and the technician says, "No, lucky you, you're the first person to try our new technology that can send all the information, get all the information, and send it to Mars without having to incinerate the original body. So the information's going to Mars. You're being built on Mars as we speak. You can go do your business there and come back, but you don't have to leave."
▶︎ 6:31 And so while the traveler is trying to wrap their head around what this means and what it implies, a technician comes in and looks all apologetic and says, "I'm so sorry. There was a glitch that we didn't realize, and so this body here on Earth was damaged in the process of the scan. The heart is irreparably damaged. In about a half hour, this body is going to die. But hey, don't worry, because you're on Mars. You're still there, so it doesn't matter at all."
▶︎ 7:00 And what Parfit thinks is once we have these two distinct points of view, it sure seems like we have two distinct points of view, two distinct consciousnesses, suddenly it doesn't seem so clear that the person on Mars is really continuing the psychological life of the original person. Certainly, the person on what he calls the branch line, the person on Earth who's going to die very shortly or whose body is going to die very shortly, that person could rightly say, "I don't care if the guy on Mars is going to continue. I'm going to die. I don't want to die. I want to continue." We could understand what they were saying.
▶︎ 7:40 So Parfit says, "Yeah, this is a really powerful intuition, and I recognize it, but what's going on with it? How do we justify it?" And so what he says is, what we have to see as psychological theorists is really the worry here isn't just that I'm not made out of the same stuff. That the person on Mars for the branch line person, the worry isn't that person isn't made out of the same stuff as me. That person's thinking, "I'm not really psychologically connected to that person. I'm a distinct line of consciousness, even though we have all of the same beliefs, values, desires, traits, intentions, and so on, all the things that according to the psychological approach make me psychologically continuous and should make me the same person." So what's going on here?
▶︎ 8:30 And Parfit says the lesson we might be tempted to draw from the case is that psychological continuity alone isn't enough for personal identity. We need psychological continuity plus sameness of body. And the difference between what's going on in the branch line case and what's going on on Mars, the reason that we might think that the person who stayed on Earth is really the same person who stepped into the booth originally and the person on Mars is not that person after all, is because the person on Earth has both the same psychological life and the same body.
▶︎ 9:10 This is a questionable strategy for solving this problem or for describing what the difference is according to Parfit for the reasons that Locke gave, and we talked about this in the last lecture. Locke's argument, you might remember, and those who follow Locke continue to give this argument, is that really the molecules you're made of can't make any difference to whether you're the same person in the way that matters to moral responsibility, survival, and so on. It can't be just the mere fact that it's the same molecules. We're not made of the same molecules over the course of our life. We're constantly exchanging them with the environment.
▶︎ 9:53 And even if we say, but still we're the same human animal, just being the same human animal doesn't seem to make any difference. It doesn't seem to matter what kind of stuff you're made up of. It seems to matter what the quality of your consciousness is. And so a kind of example that might help to show this is, look, if we're worried about prudential concern and moral responsibility, it might just so happen that due to flukes of nature, the body you're made up of right this very moment, it contains all the same molecules in a different arrangement, but all the same molecules that once made up the body of Jack the Ripper or choose your favorite monster of history. That doesn't make you that monster. That's just the stuff. That doesn't matter to whether you're responsible for what that person did or anything like that.
▶︎ 10:45 So we can't really just say that adding the body will solve the problem. If we think that the psychological continuity that I have with my replica on Mars, if the branch line case makes me think there's never enough continuity between the person who steps in the booth and the person who comes out on Mars, whether there's a branch line or not, it's just that the branch line, by maintaining the first-person perspective of the person on Earth, lets us see that very clearly, and usually in regular transportation, since the body on Earth is incinerated immediately, we don't notice it. So the worry is that you're never really psychologically continuous enough with the person on Mars, and the mere fact that the body continues shouldn't be enough for that.
▶︎ 11:34 So maybe what we're trying to say is, it's not the mere fact that the body continues. It's just that in the ordinary case, we have the psychological continuity that we think matters to our survival and to all these practical judgments. And in the ordinary case, somehow that psychological continuity is connected with having the same body. So at least when we have the same body, we know we have the right kind of continuity, but once we see these anomalous ways of making sameness of beliefs, values, desires, and so on, by making replicas, like in the teletransportation case, we just don't know if what we're after is there or not. We don't know if that's a deep enough connection, if what we have in everyday life is really there.
▶︎ 12:21 And Parfit would challenge us here to say, I get it. I see what you think. I think that too, or I did at once. He feels he's managed to free himself from this idea that there's some deep connection to his own future. So I know you think you have it in the regular case and you wouldn't have it there, but how do you know you have it in the regular case? He says, how would you tell?
▶︎ 12:42 He said, you go to sleep at night, someone wakes up in your bed. You think that their psychology is reaching back to the person who went to sleep there the night before. When you go to bed at night, you're confident that when you wake up it will. But how would you ever know? That's exactly what it would be like for the replica. If we just put a replica in your bed, it would wake up thinking that it was you.
▶︎ 13:05 When you went to bed, you would think, I'm going to wake up tomorrow. Then the next day, someone would wake up and say, see, I did wake up today and I am the same person. But that would be the same whether it was a replica or whether it was your original body. What's different between the two cases?
▶︎ 13:22 So really what the challenge is here and what makes it a difficult challenge is that we want it to be an experiential difference. We think the experience on Earth is different. When we just ordinarily continue psychologically, our consciousness flows on in a deep way in which it wouldn't in this case. And that's what the branch line case shows. But Parfit is going to say, tell me about this. If it's experiential, describe it to me. If having the same body gives you something that might not be there, what's this factor X?
▶︎ 14:00 So that's how he responds to it. But still, he recognizes the pull of this intuition. And a lot of people have it. And a lot of people are not satisfied with that response, saying, look, even if I can't tell you what factor X is, I know that I'm worried that it's not there in this case. And so what you've described as a criterion of personal identity isn't deep enough. It doesn't give me a deep enough connection to the future person.
▶︎ 14:29 And I think that the lesson that we can learn here from the branch line case and the teleporter case is that we really do want something like sameness of consciousness in some deeper sense than merely having the same beliefs, values, desires, traits, and so on. If we think that personal identity consists in psychological continuity, psychological continuity isn't just that. And so one dissatisfaction with the psychological approach is that it doesn't quite seem deep enough. Now, there's a further question, the one that Parfit raises. Are we right about that? Is there really something deeper? But there's a reason to wonder about whether there is since we seem dissatisfied with the psychological approach as he's put it forward. So that's one kind of objection. A second objection that sort of just takes the same idea and pushes it a little
▶︎ 15:29 Further is the case of fission. And the case of fission is a case in which one person somehow splits into two people, both of whom are completely psychologically continuous with the original person. And there are different versions of the case about how this happens and how the fission takes place. Some people are comfortable enough with the science fiction hypothetical case medium to just say, let's just imagine a person one day splits like an amoeba into two exact copies of what was there before. Parfit wants to give a slightly more empirically grounded case. Empirically grounded should maybe be in scare quotes, but he wants to attend to some facts about the world that might help us imagine how this could happen.
▶︎ 16:22 So he warms us up by first pointing out that, in fact, some people have to have one hemisphere of their cerebrum excised because they have severe epilepsy. And this is a way of dealing with that epilepsy. Some people have tumors and have to have a hemisphere excised. And in fact, people, it sometimes takes a little bit of rehab and adjustment, can live perfectly well with a single hemisphere of the cerebrum. Over time, most people can learn to walk and talk and drive and reason and do all the things that they did before. So you can survive with just one cerebral hemisphere.
▶︎ 17:08 And then in some cases to treat epilepsy, they don't take a hemisphere out. But what they do is sever the connection between the two hemispheres, the corpus callosum. And when they do that in experimental conditions, they can get it to appear as if there are two distinct centers of consciousness in these two hemispheres, that each has its own consciousness. It's difficult to prove this because only one hemisphere controls speech. So all of the description of what's going on comes from one hemisphere.
▶︎ 17:44 But if you separate input to the two sides of the body and give different visual input to the left and right hemisphere, one sees a pipe and one sees a pencil. You might then ask the patient, what do you see? And they'll say a pipe. But then their left hand will suddenly try to draw a picture of a pencil or something to indicate, no, it's not a pipe, it's a pencil. So in any event, there's some reason to think that consciousness can split in this way. And this is a very controversial way of describing the case. But a lot of people, neurologists who are involved have described it that way. So it's not completely implausible.
▶︎ 18:24 And then the third thing that he has to tell us to warm us up for his case as he's going to offer it is that some people have a lot of redundancy between the two hemispheres of the brain. They usually tend to specialize. You hear about people being left-brained and right-brained. Left brain being more analytic and so on, and the right brain being more artistic. But in fact, some people have much more redundancy. So he's imagining a case that involves a set of triplets, and the set of triplets has perfect redundancy between the two hemispheres of their brains.
▶︎ 19:03 So this is the case we're imagining. We have a set of triplets, and they have a terrible accident. So let's just pick up Jill and Lil, our twins from the last lecture, and give them Till, who will be the triplet. So we've got Jill, Lil, and Till.
▶︎ 19:21 There's a terrible accident, and in the terrible accident, Jill and Lil are both sadly brain dead, but the rest of their bodies are in great condition. Till has no brain damage at all. Her brain is just fine, but she has crushing injuries to her organs that will kill her before long. So you've got two good triplet bodies and one good triplet brain with redundancy in the hemispheres.
▶︎ 19:50 What he imagines is that first the doctors come in and say, "Hey, look, we could do a brain transplant. We could put Till's brain into either Jill or Lil's body, and then you'd have one good body and one good brain, completely psychologically continuous with Till." Because they're triplets, it will really take. There's a good match between the tissue. So we could do that, and you just have to choose, should we put it in Jill or Lil? They're identical twins, so there's not much to choose.
▶︎ 20:24 So the parents are thinking, "I don't know what to do. Which one should we choose?" And then the surgeon says, "Wait, I have a great idea. There's redundancy in the hemispheres. This is a risky operation. It only succeeds 50% of the time. Let's sever the corpus callosum, and let's put half of the brain into Jill and half of the brain into Lil because they can survive perfectly well with just half a cerebrum." So we can do that. We have evidence that that can happen. And since there's a 50% chance of survival, you double the odds if you do this twice. So they decide to go ahead with it, and both operations are successful.
▶︎ 21:06 So here I'll go to the board. So we've got Till here. And then there are two transplants. One goes into Jill's body, half of Till's brain, and one goes into Lil's body, half a brain. And I'm going to take off these apostrophe S's because I want to give these two names. So let's call this Jilt and this Lilt because they have Till's half brain.
▶︎ 21:37 So we've got this situation where both Jilt and Lilt are completely psychologically continuous with Till. Till is gone. Her body's died. Her brain is distributed. The original Till, the original Till brain body thing. But now we've got Jilt and Lilt. And Jilt and Lilt are each completely psychologically continuous with Till. They now seem like two distinct people.
▶︎ 22:07 And so they're not psychologically continuous with each other after that first moment. At the first moment, they both wake up being absolutely psychologically continuous with Till when she was put under for the operation. But now they start having different experiences. They're in different rooms. They talk to different people. Different people visit them. They start changing a lot. They can't connect to one another.
▶︎ 22:37 So the question is, which, if either of these, is the original Till? So does Till survive this operation? And if Till survives, where is she after the operation? Where does Till go?
▶︎ 22:55 And so the thing that is really driving the problem here is that identity, numerical identity, is a logical relation that every object holds to itself, and it has some very specific properties. It has to be reflexive. A thing is always identical to itself. It has to be symmetric. If A is identical to B, B has to be identical to A. And it has to be transitive. If A is identical to B and B is identical to C, A better be identical to C. If one equals two minus one, and two minus one equals three minus two, one better equal three minus two. So that's transitivity.
▶︎ 23:45 Identity is usually one-to-one. To have those properties, it has to be a one-to-one relation. It can only hold to one thing. And here, if the psychological continuity theory is correct, and all you need for identity is psychological continuity, Till seems to have it to two different things. So what are we going to say in this case? The logical form of psychological continuity doesn't seem right for identity.
▶︎ 24:16 So Parfit says, well, there are really three cases, three or four, depending on how you count them. The first possibility is Till survives as both Lilt and Jilt. Till somehow survives as both of them. The second possibility is that Till survives as either Jilt or Lilt. So you could count that as one or two possibilities, but as only one of them, at most one of them. And the other is that Till doesn't survive at all. And all of those possibilities raise problems for the psychological continuity theory. So possibility one says Till
▶︎ 25:01 survives as both of them. And that doesn't seem very plausible because Till, if it's identity, has to survive as one thing. So that means we have to think of Jilt and Lilt as just one thing. And we could say that. We could say, look, Till now exists but spread out over space in two different bodies. It's a thing we could say, but it just doesn't seem to capture our sense of identity.
▶︎ 25:37 First of all, they might not even know of each other's existence. They might think that it would be too traumatic. So they whisk one of them away and they tell each of them that the other died and they don't even know that the other one's there. But also, if one of them commits a crime, is it really fair at that point to punish the other? Is it really prudential concern if Lilt makes a great sacrifice for Jilt? It doesn't seem to capture our sense of identity, so that's a problem.
▶︎ 26:11 The problem with saying that, here I'll come up to the board, that Till survives as either Jilt or Lilt is that it seems really ad hoc and arbitrary. Why one and not the other? How would we know which one? They both have exactly the same relationship to Till. And both of them have exactly the relationship that the psychological continuity theory says constitutes personal identity. So that's a problem.
▶︎ 26:41 And then finally, what if we say, well, Till just doesn't survive? And Parfit says, well, that's a problem too, because they both have exactly the relation that the psychological continuity theory says constitutes identity. And also because you can just imagine all kinds of implausible scenarios here. Suppose that Till, for instance, is a dedicated Parfitian, and she knows what Parfit says about personal identity. She's a philosopher. And she says, "Okay, so I know that since identity has to be one-to-one, if both of these transplants take, I go out of existence. But if only one of them takes, then I stay in existence."
▶︎ 27:32 So maybe then Till should have a reason to bribe the surgeon to drop one of the hemispheres going into the operating room to make sure they don't both happen because she can only survive if just one happens. But intuitively, she's lowering her chances of surviving in any meaningful way if she tries to get rid of one of the hemispheres. She's not increasing her chance of survival. So that doesn't sound like a very plausible possibility either.
▶︎ 28:03 So this seems like a real problem for the psychological continuity theory. But one thing that Derek Parfit is extremely good at is biting bullets, and he will accept very counterintuitive consequences if he thinks that's where the arguments take him.
▶︎ 28:19 And in this case, he does think that that's where the arguments take him. So he says, look, as counterintuitive as it is, the best explanation here is that Till doesn't survive this operation. That if just one of the transplants had worked, and there was only Jilt or Lilt, then Till would have survived. But if both of them do, then Till doesn't survive. And he says that sounds really weird, and the way that he tries to mitigate this weirdness is to say, well, here's what we learn from this case. What we learn from this case is there are ways of going out of existence that aren't dying. So Till doesn't survive in this case, but in his terms, Till has all that matters in survival.
▶︎ 29:16 And he says we see this in nature. Cells divide. That's not death. But when a mother cell divides into two daughter cells, the two daughter cells are not identical to the mother cell. They're new cells. They're a new generation of cells. But the original cell didn't die. Cell death is a different thing than cell division.
▶︎ 29:37 So similarly with whole beings, and with persons in particular, division is a way, division of this sort, where you've got more than one psychologically continuous offspring or successor, is a way of going out of existence. But it's not like death. It's more like cell division. And so it is not strictly speaking survival, because strictly speaking, to survive, there has to be someone in the future numerically identical to you. But it's as good as survival.
▶︎ 30:19 So then he says, look, here's how I would, I, Parfit, would describe this. We connect personal identity very closely with a lot of practical judgments that really matter to us. For instance, moral responsibility, self-interested concern, being there in the future to see our children grow up, all the things that we care about. And we think we need identity for that. And really, we think we need identity for that, because what we need for that is for there to be someone in the future who's psychologically continuous with us, at least one person in the future who's psychologically continuous with us.
▶︎ 31:02 In our world, there's never more than one. We don't have fission. We don't split in two. We don't do brain transplants, none of that stuff. So in our world, wherever we have psychological continuity, we also have identity. And so because psychological continuity is really important to us, we think that identity is really important to us. But as it turns out, the identity part isn't the important part because all the identity part is, he says, is psychological continuity when it's unique.
▶︎ 31:45 All that it is to have someone in the future who's identical to you is to have someone who's psychologically continuous, and there's only one of them. That's all the difference between identity and psychological continuity is, and you can't have more than one. And he says, look, having more than one would be strange. It could be awkward splitting the money, splitting the partner, splitting the kids, whatever. But it could also be really useful. You can get a lot more done and so on.
▶︎ 32:17 So it could have its benefits, and it could have its drawbacks. But those don't make the difference between whether you survive or not. All you need for, to have what you want in survival is for there to be at least one psychologically continuous person.
▶︎ 32:34 So he has this famous slogan that personal identity isn't what matters in survival, and that means that you can go out of existence, and it's not as bad a thing as you might have thought if you go out of existence this way. And he says, "I know this is gonna sound strange to people, but the reason that this can happen is," he says, "because the psychological account of identity." And he thinks any viable account of identity, this is something he argues for, but I won't talk about those arguments here, has to be a reductionist view.
▶︎ 33:11 And by a reductionist view, he just means the fact that we're talking about is not something over and above some more basic set of facts. There is disagreement about this in the sciences, but many people think, look, chemistry ultimately reduces to physics. Anything you're gonna talk about in a chemical transaction has to rely on what's going on at the level of atoms, and molecules and what they're doing and the forces between them, the electrochemical forces between them.
▶︎ 33:45 And so what he says is, any account of identity has to be reductionist. It's either gonna be biologically reductionist. That is what it is for someone to survive into the future or someone in the future to be identical to me will involve certain biological facts about how I'm related to them, or it's gonna be psychologically reductionist. The only thing it means to be identical to someone in the future is that certain facts hold about our relation between them.
▶︎ 34:21 In this case, in the psychological approach that he's defending, what it is for someone in the future to be identical to me is for there to be overlapping chains of these psychological connections, and then to make it identity, it has to be unique. There has to be nobody else who has that same overlapping chain of connections. So he's saying this is just a set of facts that can hold in various ways, but that the things we care about will have to rely on the facts themselves and not on what we name the facts. We call the facts identity. We call the facts survival, but the facts are a bunch of psychological connections and a few other stipulations.
▶︎ 35:09 And if what we really care about are those facts, those facts can hold to any degree, and they can hold in lots of weird ways that aren't the way we originally talked about them. So what he says is sometimes the question of personal identity and the question of survival is not about a deep fact. It's about what we wanna call a set of facts that don't hold in the usual way, where there's some anomaly.
▶︎ 35:39 So let me give you an analogy that may help here. It's an analogy that Parfit uses. Suppose there's a club, it's met forever, the same people, and they meet to discuss some particular set of topics in some particular place. And then through a bunch of circumstances that cascade, the club breaks up, but some of the members meet in a different place but talk about something different but related to what they originally talked about.
▶︎ 36:15 And then the question is, is that the same club? Did the original club now resume in some other place, or is this a new club? And what Parfit says is, you could say either thing. It's up to you. You could call it the same club, or you could say it's a different club.
▶︎ 36:31 The important point is there are some ways in which it differs from the original club and some ways in which it's the same as the original club. And what you care about is the differences and the similarities. Call it the same club, don't call it the same club. That's a semantic argument.
▶︎ 36:49 It doesn't change the facts on the ground. There's nothing deep that turns on whether it's the same club over and above the facts that we already know. There's no more information added to what's going on when you call it the same club. Similarly, if you want to say, when does somebody become bald? How many hairs do they have to lose before they become bald? The answer is, well, you could call it anywhere you want, but what you're worried about is how much hair is on someone's head. Calling it bald or not bald doesn't change that.
▶︎ 37:25 So what we care about are these more basic facts and not what they're called. And so we think we care a lot about identity, and that makes us think since identity is so important, in a case like teletransportation or a case like the fission case, there has to be a right answer about whether the person survived or not, about whether the person who gets out of the teletransporter booth on Mars is the same person or not. And we want to know that answer because everything turns on it. And he says, "No, everything turns on psychological continuity, and there's nothing you don't know about the case. You know it's a new body. You know what level of psychological continuity there is. You know everything there is to know. You have to decide whether you want to call it identity or not. And you have to figure out what those facts mean and not what identity means for moral responsibility, prudential concern, and so on."
▶︎ 38:24 And similarly, in this case, he's given us three point five bad descriptions of the case: doesn't survive as either, survives as both, survives as one or the other. None of them tracks our usual use of the word identity because this just doesn't happen in our world, so we don't talk about this kind of case. So we have to decide how we want to use our word identity in this case, whether we want to apply it or not. But whether we apply it or don't apply it doesn't change what actually happened. And since what matters tracks what actually happens, we don't have to worry about the fact that we don't have a good or clear or uncontroversial way of saying whether the word identity applies or not. That's really just about a label.
▶︎ 39:18 This point about reductionism is going to be important later on, which is why I've spent some time belaboring it. And really where we're left here is that Parfit has drawn out some really counterintuitive implications of the psychological continuity view as it's usually described, and he's acknowledged those complications, and he's willing to accept them, and he's given us reasons that he thinks are good reasons to be willing to accept them. But not everybody does, and not everybody thinks that his reasons are good enough, and I'm going to just leave that here for the moment because we will come back to see in lectures three and four whether there's an alternative. But so that's one set of challenges anyway to the psychological continuity theory. And now I want to pivot a bit and talk
▶︎ 40:16 About a resurgence of the biological or bodily criterion of identity that starts gaining ground partly in response to these kinds of challenges that make people rethink the obviousness of these brain transplant cases and what they can tell us and so on, and partly for other reasons. In the late nineteen-nineties, there was really a resurgence. For a long time, it was just about fine-tuning the psychological approach, and that was mostly what the philosophical discussion was. There were always a couple of people who said, "No, wait, don't forget that it could be biological continuity," but it was pretty muted.
▶︎ 40:53 And then around the nineteen-nineties, this started really gaining steam again. And defenders of this approach said, "Not so fast on the psychological criterion. Don't be so quick to dismiss a biological or bodily account of personal identity," and especially using development since the inception of the view. They tried to argue that there's really good reason to prefer a biological approach.
▶︎ 41:19 And a really important contributor to this discussion is a book called The Human Animal: Personal Identity Without Psychology. It was written by Eric Olson and published in nineteen ninety-seven. And Olson really did for this approach something similar to what Parfit did for the psychological approach. There was a growing body of literature and a lot of arguments out there, and a lot of them were similar, and he pulled them together, systematized them, developed them, and drew some implications.
▶︎ 41:50 And so he offered the biological criterion of personal identity, which came to be called animalism, because he did not want to talk about bodily criteria, because he thought body sounds like a bunch of stuff. What he really thought was that it was being the same human animal, the same living human animal, that is
▶︎ 42:13 The criterion of identity over time, not being the same stuff, because again, a living organism doesn't remain exactly the same physical stuff over time, the same molecules, the same matter. He argues for this biological approach largely by saying there are a lot of, so Parfit got some of the counterintuitive implications of the psychological approach, and really the ones that Parfit gets are the ones that are likely to be counterintuitive for people who want a psychological criterion, but this development of it seems somehow wrong.
▶︎ 42:53 But Olson says there are a lot of other metaphysical difficulties that Parfit didn't really talk about, and so he lays those out. And he also argues that the fundamental intuition behind the psychological approach that comes from those brain transplant cases and the prince and the cobbler that I talked about in the first lecture, that these can be captured by the biological approach if they're rightly understood.
▶︎ 43:23 So he begins by claiming, first of all, that when we ask for the persistence conditions of persons or the criterion of numerical identity over time for persons, which, as I said in the first lecture, is pretty much what the question has been all this time, we're really presupposing that a person is a kind of thing, a kind of entity that has its own persistence conditions. And he thinks that this is a controversial assumption and the fact that it's a controversial assumption and that there's really some substantive metaphysics going on in asking the question this way, a person at one time and a person at another time, when are they the same person, that are not appreciated. And so he aims to bring that
▶︎ 44:13 To understand why it might be controversial to think that a person is a kind of thing with its own persistence conditions, it will be helpful to take a moment to think about the distinction between objects or entities or substances, although philosophers distinguish these, for our purposes we can use them interchangeably. So objects or entities and attributes. According to a common and plausible metaphysical understanding, only objects or entities or substances have persistence conditions or numerical identity over time. Attributes don't, not in the same way.
▶︎ 44:49 I should note that there are metaphysical positions that deny this, very venerable ones going back to Plato, talking about the reality of universals, which is a fascinating topic that will take us too far afield. So what I'm just going to do is mention Olson's assumption. He's starting with the assumption that it's correct, this metaphysical position that only entities and substances have numerical identity conditions or persistence conditions, just so we know where we're starting. I'm going to just take that for granted from here on in to explain what Olson thinks he's up to. It's a pretty plausible assumption, though.
▶︎ 45:28 So it's worth thinking what the basis for this claim is. We might talk about the identity of attributes, but in ordinary language, I think this is something we really do assume. We talk about the identity of attributes, but when we do, we're usually not talking about numerical identity or the persistence of anything. We're talking about qualitative identity.
▶︎ 45:49 I might talk about the redness of your car, for instance. The redness of your car continues as long as your car continues and doesn't get painted another color. But the redness of your car doesn't seem like it can continue. Other things can be red like that, but the redness of your car can't come apart from your car.
▶︎ 46:12 I might say, hey, is that the same red as your last car? That's a question of qualitative identity. What I mean is, is this car also fire engine red, or do we call that cherry bomb or something like that? But I can't decide that I really like the redness of my car, but the car is old and doesn't work very well, so I'll sell the car, but I'll keep the redness and give it to my next car. I just have to get another car that has its own redness. That's the sort of idea behind saying that entities or substances have persistence conditions, but attributes don't.
▶︎ 46:51 In the terminology that Olson uses for this distinction, which he takes from a philosopher named David Wiggins, attributes like color, like redness, are called phase sortals. A phase sortal is a property that an entity can have for some or all of its history, but it's a property that it could lose without ceasing to exist. So the car could become a different color without ceasing to exist, but it couldn't perhaps be turned into a pool of molten metal without ceasing to exist. So there are some properties that can change without the thing ending and some that they can't. So those properties are phase sortals.
▶︎ 47:38 That's opposed to the substance concept. The substance concept is the concept that something has to fall under, or the attribute that it has to have is really what we think of as the essence of the thing, such that if that changes, the thing ceases to exist. It can't cease to fall under that category without ceasing to exist. So for instance, I can get a puppy and my puppy might cease to be a puppy by growing into a mature dog.
▶︎ 48:08 My puppy might be shiny coated and her coat may get dull as she gets older. She may be hyperactive, but she may get sort of slow as she gets older. But my puppy cannot cease to be a canine animal except by dying. There's no way that my puppy can then become some other thing that isn't a dog. That's the substance concept.
▶︎ 48:34 There's an old Monty Python skit about the pet shop where someone talks about the dead parrot as an ex-parrot, which sort of captures this. There's no way that something that was a parrot can cease to be a parrot without being dead, without being gone. So Olson's argument is that psychological theorists, in talking about the persistence condition of persons as opposed to of things that may have person as one of their many attributes, assume that person is a substance concept. But in fact, person should be treated as a phase sortal, an attribute of some more basic kind of thing. We humans can be persons, but we could
▶︎ 49:23 cease to be persons without ceasing to exist. And this also fits with everyday speech in a lot of ways. As children mature and start getting personality and beliefs and desires and so on of their own, people will say, "Oh, he's becoming a little person." In the vegetative state, you might say, "Well, yeah, he's still there, but the person is gone. He's not a person anymore. He's just a shell of a human animal." So this is the kind of thing he has in mind, that we humans can have the attribute of persons, and other things maybe, for all we know, can have that attribute.
▶︎ 50:06 Just like not only can cars be red, but houses can be red, and mugs can be red, many things can be red. There's always some basic thing that is red. Similarly, maybe extraterrestrials can be persons, and maybe whales can be persons, and maybe AIs will someday be persons. Maybe all kinds of different things will be persons or can be persons. Humans definitely can be and typically are persons. But there's always some more basic thing that has the attribute of being a person.
▶︎ 50:42 And so what does he mean by person here? Well, the same thing that Locke and the psychological continuity theorists mean. A subject of experience with a kind of self-consciousness, a moral agent who can be rightly held responsible for what they do, a being with beliefs and desires and intentions and values, and all those things that we care about, that get preserved if you get your hemispheres transplanted, at least by supposition. So that's a person, and we can become those things as we mature, as our brains develop, and so on. But what's becoming a person is a human animal.
▶︎ 51:22 So his argument for this depends upon some metaphysical assumptions, which he makes very explicit. And again, these are not uncontroversial, but these are all debates that have been going on for many millennia, so we're not gonna solve them. So it's best just to be upfront with what you're assuming and showing where it leads. And so one of the things he assumes is that each entity can have at most one substance concept. That is to say everything that is a substance has one and only one set of persistence conditions.
▶︎ 51:56 Now, this is something that Locke, by the way, doesn't share. Locke is called a nominalist. He doesn't think the world comes, at least the world we experience and talk about, pre-carved into objects that are of one and only one kind. He thinks I'm a human, I'm a person. Humans and persons have different persistence conditions. It just depends which you're talking about, what you're interested in.
▶︎ 52:22 So it's not an uncontroversial assumption, but it is a very common assumption, and a lot of people feel that way. Like, there are just things in the world. This is a piece of paper, and there are certain persistence conditions for a piece of paper, and I can't just call it anything I want and make up new persistence conditions. The second assumption is that human animals and organisms generally are uncontroversially substances, and that their persistence conditions are uncontroversially biological. That one of the kinds of things we find in our world is living things, organisms, and organisms have biological persistence conditions and live as long as a single life continues.
▶︎ 53:07 And so a human organism lives as long as a human life is. And there might be some debate about exactly when it begins and exactly when it ends, but whenever it does begin and whenever it does end, that's the beginning and end of a human. Now, if we accept these assumptions, it follows that if psychological continuity theorists are right and person is also a substance concept, then somehow where there's a human person like me, like you, there have to be two things with different persistence conditions that are completely spatially coincident, a person and a human animal, because each thing can have only one set of persistence conditions.
▶︎ 53:52 And so if I'm a person, my persistence conditions are psychological. If I'm a human animal, they're biological. So if I'm both a human and a person, I can't really be both those things most fundamentally. There have to be two things there. And this, he says, is pretty strange and leads to a lot of difficult consequences. But the argument for it, if we accept his original assumptions, is just straightforward.
▶︎ 54:22 So Olson says, think about the implications of this. I'm going to go back to the board. So you have a typical human life. A typical human life starts with an infant plus or minus, somewhere before birth, let's say a fetus plus or minus some. And then it ends with biological death. And so here is a human life.
▶︎ 54:58 Now, at some point in this human life, there's a person. Because when we're talking about personal identity, we're talking about us. So we're talking about something that happens in a human life. But the fetus isn't a person. Nobody has psychological continuity with a fetus. A fetus doesn't have enough psychological states, doesn't have beliefs, desires, intentions, values that can be continuous, isn't laying down memories.
▶︎ 55:30 So it's actually pretty late when suddenly a person emerges. And then we imagine there's a person for a long time, and then, unfortunately, this person falls into a persistent vegetative state, so the person ends here. But the human can go on for quite some time in a vegetative state. So that's when the human animal ceases to exist. And he says, look, if a person and a human animal are distinct entities, they're distinct things, how are we to describe what's going on here? 'Cause it looks like the person pops into existence here.
▶︎ 56:12 And if the person pops into existence here, what happens to the human animal? Where does it go? There's two possibilities. One is that it ceases to exist and is replaced by a person. But then that seems really weird. We don't usually give condolences to parents when their child suddenly can speak and demonstrate moral reasoning or something saying, "Oh, I'm so sorry that your child died, but at least you've got a new person here," or something like that. That doesn't seem right. You don't go out of existence by gaining capacities.
▶︎ 56:51 And then what happens at the other end when the person ceases to exist? Well, then there's still an animal here. Where did this animal come from? If we thought that the animal went out of existence here, is this the same animal that went out of existence here and now comes back? Where did it come from? Or if it's a different animal, where did that come from? So this all seems very strange.
▶︎ 57:22 It seems like we're going to have to want to say that it's not that the animal goes out of existence, the animal is there all the time, but somehow a second thing comes into existence and remains spatially coincident with the animal for most of the time the animal's in existence. And we can say that. There are metaphysical views that talk about two different objects occupying the same space at the same time, but having different persistence conditions. And the standard example of this here is a statue and the material out of which it's sculpted. So take, for example, the David, and the marble from which it's crafted. The marble was there before the statue, and the marble could continue to exist after the statue got destroyed, if the statue was defaced in various ways so that it was no longer recognizable as a statue, but could still be pretty much the same chunk of marble.
▶︎ 58:23 So it's possible to say there is a metaphysical view that says there really are two coincident things there. They have different persistence conditions. But if we take this route with persons and human animals, and some philosophers have, this is one way in which people have tried to answer Olson. Olson says, we've got this really strange situation during the time that we have both a person and a human animal, because they're made up of exactly the same matter. And that means that anything that the person does, the animal does, and anything that the animal does, the person does.
▶︎ 59:05 Just when you think of the statue and the marble, you can't deface the David without defacing the marble, without doing something to the marble. You can't exhibit the David without exhibiting the marble. You can't polish the marble without polishing the statue. The same things have happened to both of them. So he says, that means that during the time when there is both a human person, a human animal and a person present, during that period from the P to the PVS there, the human animal will be doing, saying, and thinking everything that the person does. Because after all, it's thinking with this brain, it's speaking with this mouth, these vocal cords are vibrating, it's in the same place.
▶︎ 1:00:02 And so every thought, he says, will have two thinkers, a person and a human animal. And every utterance will have two speakers, a person and a human animal. So if I say, "I'm a person," I'm saying something both true and false, because simultaneously, and with the same words, there's an animal saying the false thing, "I'm a person," and a person saying the true thing, "I'm a person." And he says, "This is really much too complicated." This doesn't have to be this complicated. We're tying ourselves into knots trying to make a person a distinct thing, since we know that an animal is a thing.
▶︎ 1:00:43 And so if there's one thing there, it has to be an animal. So if we want to talk about the person as a thing, we have to have two things, and that just makes for this crazy metaphysics. There is a much simpler way to describe this, and that's the way that I mentioned before. Take person to be a phase sortal of a human animal. So according to this understanding, questions about the numerical identity of a person over time are like questions about the identity of a trombone player over time.
▶︎ 1:01:17 We can say, "Is that the same trombone player that we saw before?" But what we really mean there, for the most part, is, is that the same thing that was playing trombone before that we saw? That is, is that the same human trombone player? You can talk about someone being a different trombone player after the accident because he can't reach the C, which is apparently the furthest reach on a trombone. But there we're talking about qualitative identity. If we want to know, is that the person we saw before? Is that the trombonist we saw before? You're saying, "Is that the same human being?"
▶︎ 1:01:56 So asking for the criteria of numerical identity over time on this view is making a mistake. It's like the same mistake you would make if you asked about the numerical identity of the color of my car over time. The color of my car doesn't have numerical identity. It's a phase sortal, and that's exactly what Olson thinks personhood is too. You're asking, is this the same human being we saw before when you ask, is this the same person? Now, as we saw, psychological
▶︎ 1:02:29 Continuity theorists frequently test where a person goes when psychology and biology come apart by testing our practical judgments about moral responsibility, prudential concern, and other judgments that we tie to personal identity. And they say, "But look, that always goes with the psychological stuff and not the biological." And Olson says, "I don't deny that intuition. I don't deny that we think that moral responsibility and self-interested concern and worries about continuing to see our children grow or whatever it is, whatever you want to say, psychological theorists, I don't deny that those go where psychological continuity goes." But he says, "I can explain using the biological criterion what that means in a different way than you do."
▶︎ 1:03:25 And so what he says is, you're assuming that because moral responsibility and self-interested concern and these other sorts of practical matters go with psychological continuity, they must also go with identity. But you only think that because in our world, they do. Because in our world, we don't have brain transplants and so on. So he's really hearkening back, and he makes explicit use of the sort of thing that Parfit talks about when he talks about the fission case and so on, which is we're mistaking the fact that what we care about usually goes with identity for the fact that it must go with identity, as opposed to the fact that what we really care about is this other thing, psychological continuity, that usually goes with identity but doesn't have to, but can come apart from it. That's what we saw in the fission case. What matters in identity can go on to these two fission descendants, neither of whom is identical to the original person.
▶︎ 1:04:45 So what Olson says is, sure, in our world where we don't have fission and brain transplants and so on, the psychological continuity goes with the biological continuity, which is the thing that really gives you identity, the biological continuity. And so it's sort of safe to think of it as going with identity. But in a world where the psychological continuity could go elsewhere, then that would have to be a world where we would have to say, in virtue of your psychological continuity going someplace else, but you staying here, somebody else may become responsible for what you did, or you might be right to have prudential concern for someone who isn't you. In our real world where identity and psychological continuity don't come apart, that's never the case. But in a world where they did come apart, it could be the case.
▶︎ 1:05:47 So if you go back to the prince and the cobbler, one of the things he said is, if the prince had been a terrible tyrant and the peasants were coming with pitchforks, they should go for the person in the cobbler body if they want to get the prince. And what Olson would say, the way that he would describe it, is he would say, it's the cobbler is still the cobbler. The person in the cobbler body is still identical to the cobbler, and the person in the prince body is still identical to the prince. But now we want to say, instead of the prince being responsible for what the prince did before, he's responsible for what the cobbler did before. And instead of the cobbler being responsible for what the cobbler did before, he's now responsible for what the prince did before.
▶︎ 1:06:37 And so the way that Olson puts this to try to give it a little clarity is to say, you might think of being the same person as something like being the same office holder. And being the same office holder gives you certain responsibilities that maybe were taken on by someone else. So if I take over as president of the club or dean of the college or CEO of the corporation or whatever, I'm responsible for debts that were incurred by my predecessor, even though that predecessor isn't me, because I'm the same officer and it's the office that has the debts, not the individual who holds the office. And similarly, a good leader who's going to hand over the office to someone else will try to hand it over in good shape. They have prudential concern for the next officer, even though the next officer isn't going to be them.
▶︎ 1:07:36 And he says, look, we can think of personhood, being the same person as like that. If my personhood could somehow be continued in somebody who isn't me in virtue of a brain transplant, then all of those practical judgments that usually go with identity just don't go with my identity anymore. They go with the office of personhood or something like that. So in this way, he says, look, we can capture those intuitions. We can make sense of how we respond to these hypothetical cases without having to say that there is such a thing as personal identity. And we can avoid all the metaphysical awkwardness. And that's why we should hold a biological theory.
▶︎ 1:08:21 of identity rather than a psychological one. Now, these are very powerful arguments and they need to be taken seriously. But I just want to point out in conclusion, before I go on to look at another approach, that of course the biological account isn't without its own difficulties. I won't go into them in as much depth as I did with the psychological approach. And I won't need to, because many of them mirror objections from the psychological approach.
▶︎ 1:08:51 So first, I think it's just worth pointing out that biological theorists, because it's so obscure to say what psychological continuity is and so on, just take it for granted that we know what biological continuity and biological life is and we can tell when a life ends and so on. It's not that simple. And there are lots of very difficult questions about what constitutes a single biological life and when you have two biological lives, and your microbiome is made up of distinct cells, bacteria and so on that are not identical to you but are part of your metabolic system. So there are lots of really interesting questions in the philosophy of biology that just get assumed to be settled in this. So that's one thing to bear in mind about the biological approach.
▶︎ 1:09:45 And the biological approach, like the psychological approach, is a reductionist account of personal identity in the sense that Parfit described and that I described earlier. And any reductionist account of personal identity is going to be subject to its own version of many of the kinds of problems of duplication and splitting and so on that we talked about before. So since we actually do have biological instances of living organisms splitting in two, Olson is going to have to talk about his own version of the fission problem. What would happen if somehow something at the scale of a human could split in two? What would we say about identity then? Because it's really important to him that identity is the continuity of a single life. And so he would have some problem then.
▶︎ 1:10:38 Also, the things that he says about the endpoints of a life and how difficult they are for the psychological view. What are we going to say during the time there's a fetus but not yet a person, or no person but still a human organism? There's a version of those that apply to the biological case, at least as Olson gives the biological criterion. Because as I mentioned, for him, it has to be a living human organism. He really wants to say it's not a body, it's not a mass of stuff. It's a living human organism.
▶︎ 1:11:13 So he might not have a problem about the fetus, but he has a problem about zygotes or single cell germ cells, which are not quite yet human organisms, but are continuous in a way with the thing that becomes the fetus. And he says they're not human organisms, so the fetus can't be identical to him. But it's just as troubling that you can raise the same troubles about things popping in and out of existence or having to coexist with zygotes and fetuses that he does with fetuses and persons.
▶︎ 1:11:50 And at the other end of the scale, since he doesn't believe in bodies, he says we're talking about human organisms. When an organism dies and you have left a corpse, for him, that corpse is not the same thing. It's not the same entity as the organism that was there a minute before. So now there's suddenly a thing that pops into existence when an organism dies at the moment of its death that looks just like it and is composed of the same matter. And similarly, you can have problems along the lines of having to have collections of matter, bodies and living organisms as distinct things, which he's going to have to say. So that's going to be a problem for him. There are versions of the biological approach that don't insist that we're talking about a living organism, but they have their own difficulties. And that's why Olson offers the version he does.
▶︎ 1:12:53 And then finally, because of these other problems that I've discussed, when Olson really gets pushed, and when the biological theorist in general really gets pushed to say, well, exactly what has to stay the same in order for the human organism to continue, they're going to be led to some very counterintuitive results. And basically not everybody answers it the same way, so it's really much too big a literature to talk about here. But since he's given a very strong version of the view, Olson is a good person to think about.
▶︎ 1:13:34 So for instance, when he's really pushed to say what has to continue for an organism to continue, his answer finally is that it has to be the continuity for a human organism of the same brain stem, because that's what covers all the metabolic activity. And so he's led to these very counterintuitive results, like if you could take my brain stem and put it in a vat of nutrients, I would continue to exist. But if you could give me a prosthetic brain stem so that I didn't even notice that I had a prosthesis, I would have died. And so it's not easy for any of these views, because the phenomena are so complicated, to really give a concrete picture that doesn't run into these difficulties. And so though Olson has shown some really serious difficulties for the psychological approach, it's important to remember that his approach also has problems.
▶︎ 1:14:33 And then finally, a lot of people just are not pleased with the kind of austere metaphysical question that Olson recommends. They don't even think it's contentful, because what Olson is saying is like, "Whatever you care about, talk about what you care about. That's fine. But I want to know the real truth of what it is for you to continue to exist independent of anything we care about or any practical interest that we have." And he says, "Only a metaphysician could care about this question. I don't think this is a question most people care about," he says, "but if you really want to know the truth..." And a lot of people say, "Well, how do we even know what we're talking about if we're talking about something that's us and yet independent of anything we care about?" So I will leave this disagreement here. As you can see, there's a lot of strengths and weaknesses on each side, and in the next lecture, we'll talk about some alternative approaches.