# Are You Your Mind or Body?

Speaker: Marya Schechtman
Course: Personal Identity and Narrative
Watch: https://ergo.org/videos/marya-schechtman-are-you-your-mind-or-body
Transcript: https://ergo.org/videos/marya-schechtman-are-you-your-mind-or-body/transcript/
YouTube: https://www.youtube.com/watch?v=rJOYA64UzEM

When quoting, name the speaker and link to the watch URL.

What makes a person at one time the same person at a later time? Marya Schechtman walks through the core features of this question, beginning with the distinction between numerical and qualitative identity and the classic Ship of Theseus paradox. She then turns to the two leading answers: the bodily criterion, which ties identity to biological continuity, and the psychological continuity theory, which ties it to memory, personality, and mental life. Using vivid thought experiments, from Locke's prince and cobbler to Freaky Friday scenarios and evil neurosurgeon cases, Schechtman shows how philosophers have tried to pull apart biology and psychology to determine which one truly grounds personal identity. She explains why psychological continuity has become the dominant view, tracing how concerns about moral responsibility, prudence, and survival seem to follow the mind rather than the body. The lecture closes by previewing objections to the psychological view and hinting that the bodily criterion may have been dismissed too quickly.

## Three Features of the Identity Question

The philosophical question of personal identity in the modern era has three main characteristics, and we've actually already really seen them in the description of the question so far, but it's worth making them more explicit and also introducing some of the technical terminology that philosophers tend to use in discussing them.

As we've already seen, the question is a question of personal identity over time or a diachronic question, as opposed to a question of identity at a time, what makes something a single individual at a time, which would be a synchronic question. So this is a question of what makes a person at two different times or people at two different times one person, one distinct individual instead of two.

## Identity Over Time vs. Identity at a Time

And as such, philosophers generally view it as a sub-problem of a much more general question about the identity of changing objects over time. Any object with any complexity is going to change a little bit over time. Some changes seem to bring an end to the object. Some changes cause it to go out of existence. But other changes it can survive. It just persists through them. It's the same individual, just changed. And so the question is, how do we make the distinction between the changes that cause the end of the existence of something and those changes that it can survive?

And there is an ancient problem about this with respect to ships, which you may have heard of, called the Ship of Theseus. In Greek mythology, Theseus was the mythical king of Athens. He slayed the Minotaur and saved the children of Athens from King Minos. And after that, he escaped to a ship by going to Delos. And each year in antiquity, according to this myth, the Athenians would commemorate this great achievement by taking a trip on the ship that Theseus used to go to Delos, and they would take that ship to Delos and honor Apollo, and this was an important ritual for them.

## The Ship of Theseus Paradox

But the puzzle that gets raised as early as the first century by Plutarch, not only did Plutarch raise it, but he talked about people who had already been discussing it before him. So it's a very ancient puzzle is, what happens if the ship changes some planks? This is a wooden ship, and we assume it's making the trip and it's making the pilgrimage, and eventually out there on the sea, the salt water, a plank will rot and it gets replaced. Well, you can replace the plank of a ship and it's still the same ship. It's no problem.

But the paradox of the Ship of Theseus arises when we think of time going on and all the planks of the ship being replaced one by one. So the first plank rots, you replace it. A little bit later, a second plank rots, gets replaced. And over many decades, you end up with a ship that has no wood whatsoever in common with the original ship. Is it still the Ship of Theseus or not?

Internal to this myth, it's very important whether it's the Ship of Theseus or not because Apollo cares about it. And it's a puzzle. And philosophers debated it at the time and they continue to debate it. It's had many bells and whistles added to it, but it still remains a puzzle that people debate.

## From Ships to People: The Persistence Problem

And philosophers think of the question of personal identity as very much like this question, only it's about people, not ships. So when we think of applying it to the problem of personal identity, I'm cleaning the attic, I find a picture of my tenth birthday and I look at it, and I may be amazed by the fact that I have changed in almost every respect from that 10-year-old in the picture. I don't look like the 10-year-old very much. I'm physically very different. The matter that makes up my body is different. My psychology has changed immensely since I was 10 years old. My social world has changed. What I do every day has changed. Almost everything is different between now and when I was 10 in that picture.

And I may feel very far removed and alienated, and nevertheless, I recognize that person as me. Looking at a picture of my 10th birthday is different from finding a picture of someone's 10th birthday in a flea market and looking at that. I recognize the 10-year-old in my birthday picture as me, and the question that people ask is, what is it that makes that 10-year-old me? Everything has changed. What stayed the same? Why is this one particular individual?

So this is the question of personal identity over time, is trying to figure out what relation I have to that 10-year-old, what relation a person has to herself in the past and future in virtue of which she's the same person.

## Numerical vs. Qualitative Identity

The second point is that this question is not only a diachronic question of personal identity, but it's specifically a question about numerical identity rather than qualitative identity. And so numerical identity is a question about whether we have one thing or two, at the two times that we identify a person. We identify a person at one time and another. Is it the very same individual? Whereas qualitative identity has to do with what people or objects are like, their qualities.

So we talk about identical twins. Often there are some differences between them qualitatively. They don't look or talk or whatever exactly alike, but they're very, very much alike, and that's why we call them identical twins. But we're talking about qualitative identity. Nobody thinks that identical twins are one individual. They're two distinct individuals. They're just individuals who are very much alike.

So consider identical twins Jill and Lil, who I will introduce here because they'll be recurring characters as we talk about personal identity, who are so much alike that really nobody can tell them apart. They're just qualitatively almost exactly identical. But they are two people, and that shows that two things can be qualitatively identical without being numerically identical. And also we know that things can be numerically identical without being qualitatively identical, because we just talked about how I'm qualitatively so different from my ten-year-old self, and yet we think I'm numerically the same person. So the question here is specifically about numerical identity. And finally, it's a metaphysical

## Metaphysical vs. Epistemological Questions

rather than an epistemological question. Metaphysics is roughly about determining how things are in the world at the most fundamental level. Epistemology is about knowledge, how we know things, what it is to have knowledge, what it is to be certain that something's true. The question that people are asking, that metaphysicians are asking about personal identity over time isn't ultimately about how we know that someone is the same person, but rather what actually makes them the same person.

To go back to Jill and Lil, this is a cartoon example, but I think it will be helpful in seeing what the distinction is. Suppose that Jill and Lil's parents were aware from the beginning that it was going to be impossible to tell them apart. From day one, Jill is always dressed in red and Lil is always dressed in orange, and that's the way you can tell them apart. It's a good way of telling them apart, provided that they stay very young and they can't go and mischievously change clothes to confuse people. But it isn't what makes Jill the same person over time that she always wears red.

It could be that I can tell that this is Jill by seeing that she's wearing red, but that's not what makes her the same person who was wearing red yesterday. It's just how I find it out. We can see this quite clearly because when they do get older, if it were a sitcom or a Disney movie, they would switch clothes and all sorts of hijinks would ensue. What we're interested in, and this is going to be important, is what actually makes someone at one time the same person at another time, and not how we know they are. The question of personal identity with which we're starting is a question about what connection has to hold between a person at one time and a person at another time to make them numerically the same person.

## Necessary and Sufficient Conditions

And philosophers often describe this in terms of finding the necessary and sufficient conditions for someone at one time being the same person as another time. And what they mean by this is that they want to find a relation such that if that relation does not hold between a person at one time and another time, they can't be the same person, and if it does hold, they must be the same person.

So they're looking for the minimum condition, what really makes them the same person, and they often talk about this in terms of a criterion of numerical identity over time or a criterion for the persistence of a person over time.

## The Bodily Criterion: A Commonsense Answer

Once we've laid out all this nitty-gritty detail about what the question is, the answer to the question might seem obvious. I think a lot of people have the response that, well, if we're asking not about the identity crisis sense of identity, but we're asking about this very literal basic, do the police have the right man? Is that your child that you're picking up at daycare question of personal identity. What makes someone the same person at two times in this sense is having the same body or being the same human organism or human animal or human being, however you want to put it. That is how we re-identify people in everyday life. That is the way that we re-identify people.

When I go to meet my friend at the coffee shop because we made a plan to meet for coffee, I go in and I scan the room and I look and find the human being who I recognize to be the human being that I associate with my friend, and that's the table I go to, the one where the same body, that is, the body of my friend is. If we're looking for the person who committed the crime and we want to make sure that we've got the right person, what do we use? DNA and fingerprint evidence and other biometrics, just like the biometrics they use at airports and other places to make sure you're the person who bought the ticket or you're the person whose passport you're holding or whatever.

And similarly with all the stories where someone shows up claiming to be the long-lost heir at the funeral, well, if you want to know if this really is the long-lost heir or the Empress Anastasia or whatever, you're going to try to make sure that this is the human being that left all those years ago or has been missing all this time. So it would seem that a very commonsensical answer here is that it's just being the same human that makes you the same person over time.

## Psychology Over Biology: The Dominant View

But the most dominant view of personal identity over the last many hundred years actually argues that this is not the correct criterion of personal identity over time, and that the reason that we think it is is because we're confusing an epistemic criterion of identity for a metaphysical criterion. Nobody is going to argue against the claim that we do in fact re-identify one another by re-identifying human bodies. That's how we see people. You go to daycare, you see your child, you hear the voice. These are all going to be physical things about the human body. That's what we do, and it's a very reliable means of re-identifying people in the world in which we live.

But that doesn't mean, according to these theorists, that it's what makes us the same person over time any more than wearing red clothes is what makes Jill the same person over time. So these philosophers argue that what really makes someone the same person over time is the continuity of their psychological life. And that our metaphysical criterion of identity should be psychological rather than biological. That is what makes me the same person that I was on my tenth birthday is that I'm psychologically connected to that ten-year-old in the right way, not that I'm biologically connected to her in the right way.

Now, in ordinary life, biological and psychological continuity almost always occur together. When I re-identify someone through sameness of body, and I'm like, "Oh, that's my child, that's my friend at the coffee shop," and so on, what I will find is they're also psychologically continuous with the person that I was looking for. So when I go to meet my friend at the coffee shop, I recognize her by her body, but when I go up to her and say, "Sorry I'm late," and she says, "Yeah, right. You're always late," in the harrumphy and exasperated voice that she always does, and we have our little back and forth about that, and then we sit down and start talking, I know it's her. She shows the same sense of humor. She remembers what we were talking about last time. She gives me the same sage advice. She remembers what I expect her to remember and knows the people I expect her to know.

So I find psychological continuity where there's bodily continuity, and I expect it. So because biological and psychological continuity almost always go together, biological continuity is a really reliable indicator of personal identity, whether that identity depends on biological continuity or psychological continuity. They always occur together. We're really confident we've got the same person, but we don't know which of them is making them the right person. Just like, we see the red clothes, and they're a reliable indicator that we're encountering Jill, but nobody thinks that's what makes Jill Jill.

So if what we're interested in is the metaphysics of personal identity, we need to find a way to determine which of these typically co-occurring forms of continuity, biological and psychological, is the one that's necessary and sufficient for numerical identity.

## Thought Experiments: Pulling Apart Two Criteria

What we need to do is find which of these two, biological or psychological continuity, is really doing the work. And to do this, we need to determine what would happen if they came apart. So if we end up with two people, one of whom, let's call them person one, is psychologically continuous with an earlier person, call him Bob, but not biologically continuous with him, and another distinct person is biologically continuous with Bob, but not psychologically continuous. If we could figure out which of person one and person two was numerically identical to Bob, we'd know whether we need psychological or biological continuity to be the same person.

So that's the way in which these theorists have approached the question and the way in which they've thought about trying to answer it. Now, of course, there is no easy way to do such an experiment in actuality. We don't know how to prize apart the biological and psychological continuity of a mature, healthy person, but we can do it in thought. And this is the method that psychological continuity theorists have used to argue for the view that it should be psychological rather than biological continuity that's our criterion of numerical identity over time.

## Freaky Friday and the Prince and Cobbler

So they say, look, it's really easy to imagine biological and psychological continuity diverging. We do it all the time, and when we imagine it, we see right away that the person goes where the psychological life goes and not where the body and lump of stuff goes. And we are very familiar with the kinds of cases that they're thinking about. They're very familiar from popular culture and especially science fiction.

On *Freaky Friday*, a mother and a daughter, through some mysterious fortune cookie incident, appear to swap bodies. That is, after this magic fortune cookie incident, the psychological life of the mother continues in the body of the daughter. So the body of the daughter is suddenly thinking, "Wait, how am I gonna go to work like this? I have all these things I'm supposed to do. I don't know if they'll let me drive." The psychological life of the daughter goes to the mother. So the erstwhile body of the mother is thinking, "I'm in this old body. How am I gonna go to school like this?" And the way we describe this quite naturally is saying that the mother and daughter swapped bodies.

And this is the kind of case that philosophers of personal identity use. In fact, John Locke, who's responsible for much of the structure of how we talk about the problem of personal identity today, although body-swapping puzzles existed long before him, he introduces a similar case that has become very, very important in the discussion, and it's just a straightforward case in which he says, look, imagine the consciousness of a prince entering the body of a cobbler, so that what you have is someone with the body of the cobbler and the consciousness of the prince. Who is that person, the prince or the cobbler? And he says everybody sees that that will be the prince. It's the prince in the cobbler's body, not the cobbler with some kind of psychological break.

These theorists depend on us having these intuitions, and they generate many, many types of cases that are like the case of the prince and the cobbler that they think we'll react to in the way that Locke thinks we'll react to the prince and cobbler case. And most of the cases that are used now are more science fiction-y and technological, so there are brain state transfer devices, and there are brain transplants, and there are many variations on these things. But the idea is always the same. If you have a case where biological continuity goes one direction and continuity goes one direction and psychological another, the person goes with the psychological continuity.

## Out-of-Body Experiences and Vegetative States

It's probably easier to see this even in cases that are not these hypothetical science fiction-y cases, but just by looking at the fact that there are in fact many people who claim to have experienced separating from their bodies in astral projection, in near-death experiences, in certain types of meditation. People say, "I looked down at my body." "I saw what people were doing, working on my body in the emergency room," or, "I saw my body lying in the bed." If you can look at your body from the outside, if you can leave your body, then you can't be identical to your body. You can't separate from yourself.

So whether we believe these experiences are real or whether they really happen, all the psychological theorist needs is that we agree that if they did happen, the person would go with the consciousness. If we can imagine them coherently, then what would we say about where the person is? And I think most people would say, especially in something like a near-death experience where someone says, "I saw my body." "I heard my loved ones calling to me. I saw a tunnel." Whatever you think a near-death experience really is, if that really happened, that would be you continuing, if that's what happened. So that's the argument, in any case.

And also, we can look at things from the other side, too, and look at some real cases where the cases themselves aren't controversial, that they could and do happen. It's just a question of what we're gonna say about them. So there are real cases where psychological and biological continuity come apart, and in particular, this happens when psychological continuity seems to cease while bodily continuity goes on. So the clearest case of this is a permanent vegetative state. If someone has a brain injury or an accident where they're in a vegetative state and are not expected to recover, the human animal is still there. It's still alive. It can still do all kinds of metabolic things. It needs a lot of support, but the human life goes on. That's pretty uncontroversial.

And the psychological life is believed to stop entirely. People in a vegetative state are believed not to be conscious at all and not expected to regain consciousness. A lot of people feel that if they were to fall into such a state, they would be gone. That would be the end of them. That's tantamount to death. And a lot of loved ones of people who actually experience this unfortunate state feel the same way. "My loved one is gone. My child's gone. My spouse is gone. There's just the body they used to inhabit that's left."

And that really is a reaction that people have to these cases, but it's not an uncontroversial reaction. Other people feel differently. But still, what psychological theorists think is even though there's going to be some disagreement and not everybody is gonna react in exactly the same way, if you look overwhelmingly, we associate the continuity of the person with the imagined, in these imagined cases, with the continuity of the psychological life. And in order to drive home this argument

## Moral Responsibility, Prudence, and Survival

And really get us to see it, these theorists often focus our attention on some of the reasons that we find it so important to re-identify people, and they point out that those reasons are connected to psychological features of the person and not to biological features of the person. So there's a host of practical matters that rely on being able to tell whether we're dealing with the same person at two different times. That's where I started this discussion of this question of personal identity, picking up the child at childcare, paying back your friend, meeting your friend in the coffee shop, all of those.

But in order to really focus us, philosophers have looked at three main types of practical connection between identity and psychological continuity that they think are going to really show us that it's psychological continuity and not biological continuity that is required for personal identity. And the three are these. One is moral responsibility. We typically think that it's appropriate and reasonable to hold a person morally responsible only for actions that they take, only if they're the person who took that action. With some complications that we can think about, direct or collective guilt or something like that, those can usually be explained by something that the person themself did, some form of negligence or something.

So let's just stick with the canonical case, in which a person is praised or blamed for something. We think that praise or blame is only appropriate and just if they are in fact the person who did that thing. So if I'm getting the medal for saving the child who was drowning, I should be the person who saved the child. And if I am getting arrested for some crime, I ought to be the person who took the crime, who undertook the crime. Otherwise, it's not just to punish me.

The second is prudential concern. We think that it makes sense for a person to have a kind of concern for their own future well-being that they don't have for the well-being of others. It doesn't mean they care more about their own future well-being. People can care as much or more about the well-being of other people as they do themselves. But there's a special kind of concern that we have for our own future well-being.

And you can see the difference when you think about it this way. Somebody who makes it the case that many other people will suffer horribly in the future so that they can have some small, that the person can have some small pleasure now, someone like that is horribly immoral. But someone who makes it the case that they will suffer horribly in the future so that they can have a small pleasure now is not immoral, they're imprudent or irrational. So that's the difference between the two. It's a different kind of concern.

And finally, survival. This is a somewhat different kind of concern, but it's taken for granted that people have strong feelings about their own survival. They can be complicated. They can be many different kinds of feelings. Most of us want very much to continue to survive. We want to be there in the future. We want to make it through whatever thing we're worried about.

You might be in a situation where you don't want to survive, but then you would still care about whether you survive or not. It's not a matter of indifference to us whether we survive or don't survive. But what it is to survive is for you to be there in the future. That's the definition of it. If I'm going to survive, there has to be someone in the future who's numerically identical to me.

So personal identity is connected closely with moral responsibility, prudential self-interested concern, and survival. And the idea is that if we want to know what's required for personal identity over time, we should think about what's required for the appropriateness of moral responsibility or attributions of moral responsibility, self-interested concern or prudential concern, and our interest in survival. The thought is whatever it is that makes someone the same person over time should help explain and justify why we connect these practical judgments so closely to personal identity.

## Practical Concerns Follow the Psychology

And what they say is that if we think about it for a minute, it's clearly not just having this same physical body that's responsible for moral responsibility, prudential concern, or survival. It's rather psychological continuity. Think about Locke's case of the prince and cobbler. What Locke says, he calls person a forensic term. He doesn't mean necessarily just the narrow legal sense of forensic, but that it has to do with actions and their merit.

So he says, take the case of the prince and the cobbler. Everybody sees that when the consciousness of the prince goes into the body of the cobbler, that individual will be responsible for what the prince did before and not for what the cobbler did. So if the prince was a horrible tyrant and the peasants are coming with pitchforks and torches to roast the prince from the castle, they should be looking for the person in the cobbler's body after the switch and not the person in the prince's body. If the prince was a wonderful, beneficent person and they want to follow his wise leadership, well, if his psychology is now in the cobbler's body, that's who they should look to for their leadership and their wisdom.

And Locke talks just about moral responsibility, but it's the same with the other kinds of considerations as well. If the prince knows that his psychology is going to be put into the body of the cobbler, then if he knows that in advance, it would be very prudent of him to try to make sure that whoever's in the cobbler's body gets his wealth and power and has access to the things that the prince wants access to. And that would be the person who the princess and queen, if they wanted to continue their relationship with the prince, should talk to. All these major practical considerations that we attach to personal identity go with the psychology and not with the body.

A more present-day example of this, just to add one more example to show the kind of case that these theorists are trying to make, is the following.

## The Evil Neurosurgeon Thought Experiment

Let's talk about one of the evil neuroscientists or evil neurosurgeons who can transplant brains or do brain state transfers that have been part of the literature and the discussion for quite some time. Suppose we have an evil neurosurgeon who works for criminals, and a notorious serial killer has paid this neurosurgeon to give him a new body. It used to be you just got a new face with cosmetic surgery, but that couldn't protect you because now they can do DNA testing and other things, so he needs a whole new body. So the killer kidnaps a blameless person off the street, perhaps it's you, and takes that person to the neurosurgeon and says, "I wanna be in that body."

The neurosurgeon does whatever this technology is and puts your consciousness into the body of the serial killer and puts the serial killer's consciousness into your body. After the swap, the person in your body with the serial killer's consciousness is gonna go off and live on a beach for a while and then think about the next person they wanna kill. Meanwhile, the person with the serial killer's body and your consciousness is going to go get hauled off to prison for the rest of their life. And the idea is think about it from your first-person perspective.

What it would be like is that you get kidnapped off the street, you wake up in some new scary body, and the next thing you know, the police are arresting you and putting you in prison. This does not seem just. The police may have gotten the right man or woman or human in this case, but what they didn't get was the right person, or so, psychological theorists argue. So all of these kinds of arguments are taken to show that biological or bodily continuity is not necessary or sufficient for personal identity and that what you need is psychological continuity.

## What Exactly Is Psychological Continuity?

But what exactly is psychological continuity? I've used that term loosely. I've also talked about sameness of consciousness. I haven't really distinguished the two. I've used them interchangeably. But when you're trying to turn this into a theory of personal identity, you can't be vague like that.

If you really want to say what has to be the case, you have to say for a person at one time and a person at another time to be numerically identical to one another, we need more specificity about what this relation of psychological continuity is. And this has been troubling for these theorists. It's not easy to spell out. And so I'll say a little bit about that here, and then I'll pick it up again in the next lecture where I talk about some objections to the psychological view.

## Why the Soul Can't Ground Identity

So first of all, the idea of sameness of consciousness or psychological continuity has to be distinguished from sameness of soul. And it might have surprised you that I haven't said anything about sameness of soul yet, because very often when we talk about bodies and psychologies going different ways, that's conceived of as something like the soul leaving the body, and so why not just think of it that way? And the answer is, it's not clear what a soul is. The word soul can mean a lot of different things. And in the metaphysical context in which this discussion is taking place, and because of what's happened in the history of early modern philosophy, the soul is conceived here as just this bare, featureless, immaterial thing.

There's material stuff, the stuff that tables and chairs and bodies are made out of, and there's some immaterial stuff, and all we can really say about the immaterial stuff is that it's extended in time but not in space. But we can't say anything more about it. We can't say what it is, and very importantly, it's not available to the senses. I can't see a soul or hear a soul or touch a soul or any of those things. Even if I think I could tell when a soul is present, I can't tell when the same soul is present at two different times.

Now, a lot of times that's not how we talk about the soul in other contexts, outside of this metaphysical context. Outside of this context, sometimes we think of the soul as the bearer of a person's attributes and completely interconnected with them so that they can't come apart. So if we talk about someone having a sweet soul or a kind soul or an evil soul, we think that that soul must be kind, sweet, or evil all the time. But if we think of the soul as a featureless immaterial substratum, that's not the case.

And so what Locke argues is that, look, if we can imagine that a psychological life or a consciousness could move from one body to another, it could equally well move from one soul to another. The attributes, the beliefs, the desires could be moved from one immaterial vessel to another, because in this conception of soul, there's really nothing that prevents that. So for all we know, our consciousness is being transferred from soul to soul like billiard balls transfer momentum from one to the next, and there's just a succession of souls going through us all the time. We don't know when we have the same soul. We could never tell. And we don't know that we have the same soul we had when we went to sleep. We don't know that other people have the same soul.

And given this, the soul can't be the thing that explains moral responsibility, prudential concern, or anything else any more than the body can, or survival any more than the body can. The soul is just immaterial stuff that plays no more of a role in explaining or justifying our practices connecting identity to these practical concerns than the body does. So that's a lot, and it may not be clear, but the basic point is that no one has thought that sameness of soul could be a viable account of personal identity of the kind we're looking for here, and that's why it hasn't been part of the discussion very much. It's not that nobody discusses it. There are some people who will say this of soul views, but it's very rare, and so that's not going to do the work for us of saying what psychological continuity consists in.

## Memory as a Criterion: Promise and Problems

Locke doesn't ever talk about psychological continuity. He says that the sameness of person consists in sameness of consciousness. We want our consciousness to go on. That's what we want. If we think that we leave our body when we die, we think our consciousness continues after that. So he thinks that we should be talking about this notion of sameness of consciousness.

And a question that people have asked since Locke put this view forward is, what is sameness of consciousness? What is it for the same consciousness to continue over time? What is it for a stream of consciousness to flow on, for consciousness to continue in another body or after death? And it turns out to be a very difficult question to answer. We know that we have gaps in our consciousness. We go to sleep and we wake up. We might be anesthetized for a surgery or something like that. So how do we know when we wake up that this is the same consciousness that was rolling on before we came here?

It's not a clear notion, and so Locke is regularly pressed to explain what constitutes sameness of consciousness. Usually, he's read as saying that what makes the same consciousness over time is memory, that if I can remember an experience that connects my consciousness to it, and therefore makes me the same person who had that experience. If I remember taking an action, then that connects my consciousness to that action in the right way and makes me the person who took that action.

Now, Locke didn't say that explicitly, and I don't actually think that it's what he means, but it's a very bad account of personal identity, because we can all think of lots of examples. I can seem to remember things that I didn't do. If I remember leading the troops at Waterloo, that doesn't make me Napoleon. I can remember making that witty remark at the last party when it was really you who made the witty remark at the last party. So the fact that I remember it doesn't seem enough to make it mine.

But also the fact that I forget it doesn't seem enough to make it the case that it isn't mine. If I commit a heinous crime and then I forget it because I'm just that kind of person, it just doesn't register in my consciousness enough for me to remember it. That doesn't mean I'm not responsible for it, or at least we don't think it does. Now, Locke never actually says that it's sameness of memory, that memory makes for sameness of consciousness. That's not a thing that Locke, in fact, says. I think it's a misreading of Locke, but then we're still left without any way to explain what the sameness of consciousness is.

## The Modern Psychological Continuity Theory

Around the nineteen seventies, there was a big revival of interest in questions of identity over time in general, personal identity in particular, and Locke's view. And the theorists who were involved in this revival and who put the debate into the terms in which it's proceeding now gave up on the idea of sameness of consciousness and instead talked about psychological continuity. And so their idea was this. Look, memory is important. It can be important, but so can a lot of other psychological connections. How about the continuity of my beliefs and my values and my desires and my character traits and my intentions and the actions that carry them out? All of these things are part of my psychological life. So instead of thinking about some abstract notion of sameness of consciousness or thinking about some memory criterion of identity, we should have a psychological criterion of identity.

And the way they've spelled this out is very much like the ship of Theseus, one solution to the ship of Theseus puzzle. So one solution to the ship of Theseus puzzle says it's the same ship at the end as it was in the beginning because the planks were replaced very gradually, and because the planks were replaced very gradually, you have a functional ship the whole time. So each ship is connected to the next ship with one different plank, and it remains a ship the whole time. So as long as it's a gradual change and there's a ship the whole time, it's the same ship, the ship of Theseus. If you replace ninety percent of the planks at once, that wouldn't be the ship of Theseus. If you did it all at once, you would have dismantled the ship of Theseus and built a new ship, which might have been a replica.

Similarly, these psychological theorists say that's how it works with personal identity. Our psychological life changes gradually over time, and as long as it's gradual, there's continuity of psychological life of a kind that makes for personal identity that will explain moral responsibility, prudential concern, and our interest in survival. So on this view, what makes me the same person as that ten-year-old having a birthday in the photograph I find is that today I'm very psychologically similar to how I was yesterday, and yesterday was very psychologically similar to how I was the day before. A couple of beliefs, desires, memories will change every hour, every day, frequently, but just a few. I still have most of the same memories, intentions, desires, and so on. So today to yesterday, yesterday to the day before, and so on back to that ten-year-old.

Now, by the end of it, there might be no psychological planks in common with the ten-year-old. But because there was a psychological life that whole time that developed and changed only gradually, that's what connects me back to the ten-year-old, is that chain of psychological similarity over time. And that's something that I have to the ten-year-old in my birthday photo that I wouldn't have to a ten-year-old in some random photo that I found at the flea market, and that's how they define personal identity.

## Summary and Preview of Objections

And they add a few more stipulations that we don't have to worry about here. And this is the criterion of personal identity that really dominated the discussion of the topic for much of the twentieth century. In analytic philosophy, it remains a very important and widely held view of personal identity, but it has some difficulties. And in the next lecture, I will describe those difficulties and some of the responses that have been given to them. And I'll also show how other philosophers have taken these difficulties as well as others and used them to argue that really the biological or bodily criterion of identity was discarded too quickly, and it makes for a better criterion of personal identity.