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We've seen what Locke has to say about personal identity.

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Admittedly, only briefly, but you can see that he distinguishes between the identity of different things,

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in particular distinguishes between the identity of a physical organism and the person.

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He's got a clear motive for doing that because of the forensic importance of the notion of person, its relation to morality and desert and so forth.

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And he links personhood with consciousness. And therefore with memory.

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Now, Thomas Reed famously raised a problem case for Locke, which he put like this.

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Suppose you've got a young lieutenant in the Army. He can remember what he did as a child.

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Maybe, for example, he can remember stealing an apple. Maybe feels guilty about it.

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When he becomes a general. The general can remember what the lieutenant did, but he can't remember what the child did.

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He's completely forgotten about the Apple incident.

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Now, if memory constitutes personal identity, then it looks like the lieutenant is the same one, I'm the same person as the child.

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The general is one and the same person as the lieutenant. But the general is not the same person as the child.

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And that seems to be a contradiction because the notion of identity is supposed to be a transitive relation.

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That is, if X is identical with Y. And why is identical with Z?

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It follows that X is identical with Z. That seems to be a logical truth about the notion of identity.

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Indeed, it follows from Lightman's law.

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Well, there is a nice, elegant way of getting around this, so we introduce what's called the ancestral relation.

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You'll see. It's obvious why it's called the ancestral relation, because the classic example of this is the relation of being an ancestor.

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So look at this definition. X is an ancestor of Y if either.

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X is a parent of Y. Or X is a parent of an ancestor of Y.

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Now, when you first see that definition, you might think.

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Isn't that a bit odd because the word ancestor is not only appearing as the word to be defined.

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It's also appearing in the definition. Isn't that circular? Well, in a sense it is, but it's not viciously circular.

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And that's because we have the first clause as well. So suppose we want to identify who my ancestors are.

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Well, what this says is, first of all, my parents are ancestors.

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Okay, but then their parents and sisters, because they have parents of ancestors of mine.

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And then their parents or ancestors of mine. Because their parents of ancestors of mine and so on.

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So actually, it's very elegant, neat way of getting a recursive definition.

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The definition van sister appeals to the notion of ancestry itself.

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So it's recursive. But it's not viciously said.

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Now, consider that in the abstract, consider what we've done, we've taken the neat notion of parent,

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the relation of being a parent, and we have generated from that a more general relation that includes parenthood.

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But as it were, iterates it. So we call ancestor the ancestral relation of parent.

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Now, suppose we do the same with memory. Suppose we say.

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That's that. Ex. Is memory continuous with why?

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If either. X can remember Y's actions or.

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X can remember the actions of someone who is memory continuous with Y.

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So now what we have is that the general is memory continuous with the child

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because the general is memory continuous with the lieutenant and the lieutenant,

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his memory continuous with the child. So we get round Reid's problem by extending Locke's account.

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We don't make it rely just on what a single step memory we allow iterated memories to count as well.

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There's another advantage of this sort of approach, which is as follows.

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My continuity with myself yesterday. We're reluctant to think that that's anything to do with whether I can remember exactly what I did yesterday.

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I mean, suppose you go to a really good party and afterwards you can remember very little of what went on.

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That doesn't mean you're not the same person. Now.

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Suppose, on the other hand, do you imagine yourself through those hours? If you if you're calm.

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I realise this may be a question in those circumstances.

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But if your consciousness is continuous throughout the period, then you cannot each moment remember what happened in the immediately previous moment.

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You have it have, as it were, a continuity of experience and the ancestral relation.

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Let you build that right through the day. So you don't lose any.

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You don't have to say that at eleven o'clock in the evening, you have to be able to remember what happened at nine o'clock in the morning.

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The continuity can come through the ancestral relation. But there are, of course, lots of problems remaining.

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One problem is so-called quasar memory. If you base personal identity on memory.

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The trouble with that is something only counts as a genuine memory if it concerns your own experiences.

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Suppose I wake up. With an apparent memory of your experiences.

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Very peculiar. But would we call that memory? No, we wouldn't.

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We'd say that isn't a genuine memory. Something's gone wrong.

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Goodness knows what. But that's not a genuine memory. OK.

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So straight off, we need to say that the what we are using as a criterion of personal identity is not genuine memory.

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It's apparent memory, quasar memory.

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If we say genuine memory, then that's just going to be circular because we're only going to count it as genuine memory.

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If the we have personal identity. Another problem.

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Sleep. Well, continuity of consciousness may do the job from morning until night.

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But what about when you go to sleep? Does your consciousness then switch off?

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Well, maybe you can get round that.

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Maybe you can say with Descartes that it's of the essence of your mind that it's always thinking, maybe sometimes thinking semi consciously.

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And maybe you're going to be able to build that into some account. You can see there's a difficulty there.

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We're not going to be able to rely on full consciousness in the way that Locke wanted to.

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But what about Koma? What if someone goes into a coma?

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Suppose for a time, brain activity ceases. We have every reason to think that there is no consciousness, whatever, over that period.

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But then it revives. Would we not want to say that it's the same person?

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Particularly if they continue to act in the same way they retain memories from before and so on?

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Well, this suggests that some element of BOTTOMLY or at least brain continuity, is desirable.

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It enables you to bridge over the gaps in these sorts of cases.

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If somebody had a really bad accident, the brain appeared to switch off for a time.

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But then switched on again and things continued more or less as normal. I'm sure we would want to say it's the same person.

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We do that because largely because it's the same physical body.

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And we assume that with the same physical body. Broadly, the same mind is there.

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It's like turning your computer off and turning it on again. It's still your computer.

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It's still got all the memories and software, etc. from before. And that might lead us to think that bodily identity is really the crucial thing.

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Consciousness doesn't matter so much. What matters most is the physical seat of consciousness.

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The thing that actually causes it.