WEBVTT 00:01.050 --> 00:04.120 Professor Shelly Kagan: Last time, we turned to the 00:04.119 --> 00:06.709 question of what the metaphysical key to personal 00:06.705 --> 00:07.885 identity might be. 00:07.890 --> 00:11.290 What makes it be the case that one person, some person that 00:11.288 --> 00:14.158 exists in the future, is the same person as me. 00:14.160 --> 00:18.020 The first approach to this that we considered was the soul 00:18.024 --> 00:21.624 theory of personal identity: the key to being the same 00:21.617 --> 00:23.987 person is having the same soul. 00:23.990 --> 00:25.610 Same soul, same person. 00:25.610 --> 00:28.540 Different soul, different person. 00:28.540 --> 00:32.310 And the difficulty with that approach, even if we bracket the 00:32.310 --> 00:34.950 question whether or not there are souls, 00:34.950 --> 00:38.960 the difficulty with that approach was that it seems as 00:38.964 --> 00:42.984 though the soul could constantly be changing while the 00:42.978 --> 00:45.268 personality, as we might call it, 00:45.273 --> 00:48.173 stays the same. I have the same beliefs, 00:48.173 --> 00:51.823 memories, desires, goals, preferences and so 00:51.817 --> 00:54.567 forth. But the soul underneath it all 00:54.572 --> 00:57.232 keeps being swapped every five minutes. 00:57.230 --> 01:00.350 If the soul theory of personal identity were right, 01:00.346 --> 01:01.776 that would not be me. 01:01.780 --> 01:05.650 I would be--Every five minutes that person would die and we'd 01:05.651 --> 01:08.301 have a new person, despite having the same 01:08.297 --> 01:11.567 personality. Most of us find that a rather 01:11.569 --> 01:15.509 difficult thing to believe, that the person could be 01:15.507 --> 01:19.887 constantly changing in this way, without having any way at all 01:19.888 --> 01:22.108 to tell. And if we're not willing to 01:22.105 --> 01:25.425 accept that implication, it seems as though we need to 01:25.433 --> 01:28.513 reject "the soul theory of personal identity." 01:28.510 --> 01:31.060 Now, I use this cumbersome phrase because, 01:31.059 --> 01:34.979 of course, I'm not here talking about rejecting the existence of 01:34.978 --> 01:37.728 souls. What I'm considering right now 01:37.730 --> 01:42.200 is the question whether sameness of soul is the key to being the 01:42.204 --> 01:44.314 same person. And this is a--There's a 01:44.307 --> 01:46.337 logical distinction here that's worth drawing. 01:46.340 --> 01:51.370 Even if you believe in souls, you don't have to say that 01:51.369 --> 01:56.669 having the very same soul is the key to being the very same 01:56.674 --> 01:58.554 person. And trivially, 01:58.548 --> 02:02.328 of course, if you don't believe in souls, if you don't believe 02:02.329 --> 02:05.489 that souls exist, that you certainly can't appeal 02:05.490 --> 02:08.650 to the existence of souls, the continuity of soul, 02:08.650 --> 02:11.120 the sameness of soul, as the key to personal 02:11.118 --> 02:13.048 identity. But we might then ask, 02:13.053 --> 02:14.893 "Well what's the alternative?" 02:14.889 --> 02:19.279 Now, the natural alternative is to say, "The key to being the 02:19.276 --> 02:22.636 same person is not the sameness of the soul, 02:22.639 --> 02:26.919 whether or not it exists, but rather having the very same 02:26.918 --> 02:28.938 body." And again, although I'm not 02:28.940 --> 02:32.230 going to go on and on about this point, it's worth noticing that 02:32.233 --> 02:34.483 even if you do believe that souls exist, 02:34.479 --> 02:38.939 nothing stops you from accepting the body theory of 02:38.937 --> 02:40.717 personal identity. 02:40.720 --> 02:44.310 Nothing rules out the possibility that having the very 02:44.311 --> 02:48.581 same body is the key to being the very same person over time. 02:48.580 --> 02:52.560 Even if you believe in souls, you can accept the body theory. 02:52.560 --> 02:55.960 And it certainly looks as though if you don't believe in 02:55.960 --> 02:59.180 souls, you have to accept the body theory of personal 02:59.176 --> 03:01.146 identity. Now, as it turns out, 03:01.149 --> 03:02.819 that appearance is deceptive. 03:02.819 --> 03:05.099 There are still other alternatives open to the 03:05.099 --> 03:08.239 physicalist, but let's come to that other alternative later. 03:08.240 --> 03:11.910 Let's take a few minutes and consider the nature of the body 03:11.908 --> 03:14.828 theory, the body theory of personal identity. 03:14.830 --> 03:18.640 On this theory, of course, the secret to being 03:18.642 --> 03:22.202 the same person is having the same body. 03:22.199 --> 03:24.929 So when we ask, well you remember last lecture 03:24.932 --> 03:28.582 I was talking about how there'd be somebody here lecturing to 03:28.576 --> 03:30.516 you, philosophy, on Tuesday. 03:30.520 --> 03:32.110 Well, here somebody is. 03:32.110 --> 03:34.710 Is that the same person? 03:34.710 --> 03:38.370 Is the person who's lecturing to you now the same person as 03:38.370 --> 03:41.210 the person who was lecturing to you before? 03:41.210 --> 03:46.310 According to the body theory, the answer is--turns on the 03:46.305 --> 03:50.305 question, "Well, is this the same body as the 03:50.308 --> 03:55.038 lump of flesh and bone that was here last week?" 03:55.039 --> 03:58.889 If it is--and by the by it is--if it is, 03:58.893 --> 04:01.663 then it's the same person. 04:01.659 --> 04:04.649 So am I the person who was lecturing to you last week? 04:04.650 --> 04:08.040 Yes, I am, because it's the very same body. 04:08.039 --> 04:10.409 That's what the body theory says. 04:10.409 --> 04:12.919 And unlike souls, where it's all rather 04:12.922 --> 04:16.962 mysterious how you could tell whether soul swapping was taking 04:16.955 --> 04:19.415 place or not, it's not all that mysterious 04:19.417 --> 04:22.327 how we check out to see whether the same body's been around. 04:22.329 --> 04:27.219 Even though you didn't do it, you could have snuck into my 04:27.223 --> 04:30.403 house, watched my body go to sleep, 04:30.399 --> 04:33.389 get up in the morning, followed the body around over 04:33.385 --> 04:36.215 the course of the day, see it go to sleep again. 04:36.220 --> 04:38.860 You could have tracked that body through space and time and 04:38.860 --> 04:42.240 said, "Hey look. It's the very same body." 04:42.240 --> 04:46.370 In the same way that we are able to track in principle cars, 04:46.370 --> 04:49.510 our earlier example, and talk about yeah, 04:49.507 --> 04:54.377 it's the same hunk of metal and wire and rubber and plastic. 04:54.379 --> 04:57.119 This is the same hunk, same body. 04:57.120 --> 04:58.980 All right, same body, same person. 04:58.980 --> 05:04.900 That's the body theory of personal identity. 05:04.899 --> 05:08.239 Now, if we accept the body theory, then of course if we 05:08.242 --> 05:11.402 turn to the question, "Could I survive my death?" 05:11.399 --> 05:13.649 Could I survive the death of my body?" 05:13.649 --> 05:16.019 at first glance, it looks as though the answer's 05:16.020 --> 05:18.290 going to have to be, "Well, of course not." 05:18.290 --> 05:24.430 Because when my body dies, then, oh eventually the body 05:24.432 --> 05:27.412 begins to decay. It decomposes, 05:27.414 --> 05:31.424 turns into molecules which get absorbed into the soil or what 05:31.419 --> 05:34.909 have you. This may take years or decades 05:34.905 --> 05:39.015 or even centuries, but my body no longer exists 05:39.022 --> 05:41.352 after death of my body. 05:41.350 --> 05:45.010 And so how could I survive the death of my body, 05:45.006 --> 05:48.426 if for me to survive the death of my body, 05:48.430 --> 05:51.020 there's got to be somebody who's me, and if being me 05:51.021 --> 05:55.351 requires it being the same body, my body would have to still be 05:55.351 --> 05:57.261 around, but it's not. 05:57.259 --> 05:58.589 That's what it looks like at first glance. 05:58.589 --> 06:04.259 But at second glance we see that there's at least a logical 06:04.264 --> 06:08.964 possibility of surviving the death of my body. 06:08.959 --> 06:15.149 All it takes is for my body to be put back together. 06:15.150 --> 06:18.370 Bodily resurrection. 06:18.370 --> 06:22.560 Now I'm not going to here pursue the question of, 06:22.559 --> 06:26.749 "Do we believe bodily resurrection occurs or will 06:26.749 --> 06:29.449 occur?" I'll note that there have been 06:29.448 --> 06:32.748 religious traditions that have taught and believed in this 06:32.750 --> 06:34.570 possibility. In particular, 06:34.573 --> 06:38.663 it's probably worth mentioning that early Christians believed 06:38.660 --> 06:42.540 in something like the body theory of personal identity and 06:42.543 --> 06:46.633 believed in bodily resurrection that would happen on Judgment 06:46.630 --> 06:49.870 Day. We can certainly understand the 06:49.873 --> 06:53.413 possibility that God would perform a miracle, 06:53.413 --> 06:58.083 put the molecules back together, turn the body back on. 06:58.079 --> 07:03.289 Same body, same person, come Judgment Day. 07:03.290 --> 07:06.220 That's the possibility. 07:06.220 --> 07:09.450 So it's at least worth emphasizing the fact that even 07:09.446 --> 07:14.116 if we don't believe in souls, we could still believe in the 07:14.121 --> 07:20.101 possibility of surviving one's death, the death of one's body, 07:20.100 --> 07:25.300 if we're willing to believe in bodily resurrection. 07:25.300 --> 07:28.260 Well, that's how it looks. 07:28.260 --> 07:29.740 Now let's take a harder look. 07:29.740 --> 07:35.480 Talking that way assumes that when you put the body back 07:35.483 --> 07:41.963 together, when God puts the body back together on Judgment Day, 07:41.957 --> 07:45.087 that that's still my body. 07:45.090 --> 07:49.500 Is that right? I'm inclined to think it is 07:49.495 --> 07:51.675 right. If God gathers up all the 07:51.676 --> 07:54.526 various molecules that had composed my body, 07:54.525 --> 07:57.105 reassembles them in the right order, 07:57.110 --> 08:00.540 putting this calcium molecule next to that hydrogen molecule 08:00.537 --> 08:03.767 and so forth and so on, reassembles them in the right 08:03.769 --> 08:07.569 way--obviously if what He makes out of my body's molecules is a 08:07.573 --> 08:09.793 Cadillac, then that's not my body--but if 08:09.794 --> 08:12.524 He puts them together in the right way, that seems like it 08:12.524 --> 08:13.534 should be my body. 08:13.529 --> 08:17.709 So here's an analogy to give you a sense of what's going on. 08:17.709 --> 08:23.129 Suppose I take my watch to the jeweler because it stopped 08:23.131 --> 08:25.981 working. And in order to clean it and 08:25.976 --> 08:28.986 fix it, repair it, what the jeweler does is he 08:28.993 --> 08:32.493 takes it apart. He takes the rust off of the 08:32.490 --> 08:36.090 gears, if there are still gears in watches. 08:36.090 --> 08:37.400 Imagine it's an old stop watch. 08:37.399 --> 08:40.619 And he cleans all the pieces and buffs them and polishes them 08:40.624 --> 08:42.724 and then reassembles the whole thing. 08:42.720 --> 08:44.530 And a week later, I come back and ask, 08:44.531 --> 08:45.561 "Where's my watch?" 08:45.560 --> 08:47.520 And he hands it to me. 08:47.520 --> 08:48.670 Well, all well and good. 08:48.669 --> 08:52.059 Now imagine some metaphysician saying, "Wait a minute, 08:52.063 --> 08:54.003 buster. Not so quick. 08:54.000 --> 08:56.420 That's not my watch. 08:56.419 --> 09:01.899 Admittedly, it's composed of all the very same pieces that 09:01.902 --> 09:03.732 made up my watch. 09:03.730 --> 09:09.020 Admittedly, all these pieces are in the very same order as my 09:09.022 --> 09:12.552 watch, but still that's not my watch." 09:12.549 --> 09:15.749 On the contrary, it seems to me the right thing 09:15.751 --> 09:19.581 to say about that example is, "No, that is my watch." 09:19.580 --> 09:24.900 My watch was disassembled for a period of time. 09:24.899 --> 09:28.969 Perhaps we should say my watch didn't exist during that period 09:28.972 --> 09:31.102 of time. But it got put back together. 09:31.100 --> 09:34.340 Now that's my watch. 09:34.340 --> 09:37.550 If that's the right thing to say about the watch--and it does 09:37.554 --> 09:40.984 seem to me to be the right thing to say about the watch--then God 09:40.983 --> 09:43.933 could presumably do the same thing on Judgment Day. 09:43.929 --> 09:47.519 He could take our molecules, which had been scattered, 09:47.523 --> 09:50.103 put them back together and say, "Ha! 09:50.100 --> 09:52.430 That's your body." 09:52.429 --> 09:56.579 And if the body theory of personal identity is right, 09:56.583 --> 09:58.583 well, that would be me. 09:58.580 --> 10:00.360 So it seems to me. 10:00.360 --> 10:04.700 But there's a different example that we have to worry about as 10:04.703 --> 10:08.913 well, which argues against this proposal that the body could 10:08.905 --> 10:11.535 decompose and then be recomposed. 10:11.539 --> 10:15.099 This is an example that's due to Peter van Inwagen. 10:15.100 --> 10:17.680 He's a contemporary metaphysician, 10:17.676 --> 10:19.546 teaches at Notre Dame. 10:19.549 --> 10:27.419 Suppose that my son builds a tower out of wooden blocks. 10:27.419 --> 10:28.919 We have a set of wooden blocks at home. 10:28.919 --> 10:32.629 Suppose that he builds some elaborate tower. 10:32.630 --> 10:34.540 It's very impressive. 10:34.539 --> 10:37.199 And he says, "Please show it to mom when she 10:37.202 --> 10:39.622 comes home." And he goes to bed. 10:39.620 --> 10:40.570 And I'm very good. 10:40.570 --> 10:46.620 I'm cleaning up the house after he goes to bed and oops, 10:46.620 --> 10:49.370 I knock over the tower. 10:49.370 --> 10:51.780 I say, "Oh my god, he's going to be so angry. 10:51.780 --> 10:53.720 I promised him I'd be careful." 10:53.720 --> 10:57.780 So what I do is I take the blocks and I put them back 10:57.777 --> 11:02.537 together, building a tower in the very same shape and the very 11:02.537 --> 11:06.517 same structure, the very same order as the 11:06.515 --> 11:09.295 tower that my son had built. 11:09.299 --> 11:13.089 And in fact I'm so careful--perhaps the blocks are 11:13.089 --> 11:17.579 numbered--I'm so careful that every block is in exactly the 11:17.575 --> 11:21.825 same position as in the case where my son built it. 11:21.830 --> 11:26.890 All right, I rebuild or I build this tower and my wife comes 11:26.885 --> 11:30.565 home and I say, "Look what our son built. 11:30.570 --> 11:35.240 This is the tower that our son built." 11:35.240 --> 11:37.900 Ah, that doesn't sound right. 11:37.899 --> 11:41.969 That's not the tower that our son built. 11:41.970 --> 11:43.870 That's a tower that I built. 11:43.870 --> 11:46.480 This is a duplicate tower. 11:46.480 --> 11:51.080 Sure, if my son were to wake up and I didn't tell him, 11:51.084 --> 11:54.824 he wouldn't know that it was a duplicate. 11:54.820 --> 12:00.950 But when you take a wooden block tower apart and then put 12:00.953 --> 12:06.103 the pieces back together, piece for piece, 12:06.097 --> 12:14.437 duplicate, you don't have the very same tower that you started 12:14.439 --> 12:18.169 out with. That's what van Inwagen says 12:18.168 --> 12:21.448 and, I've got to admit, sounds right to me. 12:21.450 --> 12:23.540 If I were to point to that tower and say, 12:23.543 --> 12:26.163 "Ari built that," I'd be saying something false. 12:26.159 --> 12:29.539 "That's the very same tower that Ari built." 12:29.539 --> 12:34.079 No, I'd be saying something false. 12:34.080 --> 12:38.600 So van Inwagen concludes, if you have an object and you 12:38.596 --> 12:43.276 take it apart and then put it all back together again, 12:43.279 --> 12:48.029 you don't have the very same object that you started out 12:48.025 --> 12:50.765 with. So even if Judgment Day were to 12:50.772 --> 12:55.132 come, and God were to reassemble the molecules and resurrect the 12:55.127 --> 12:58.557 body, it's not the very same body 12:58.559 --> 13:01.439 that you started out with. 13:01.440 --> 13:06.580 And if having the very same body is the key to personal 13:06.584 --> 13:10.114 identity, it's not the same person. 13:10.110 --> 13:15.530 Come Judgment Day, we've got a duplicate of me, 13:15.529 --> 13:18.239 but we don't have me. 13:18.240 --> 13:20.760 That's what van Inwagen would say, if that's the way bodily 13:20.760 --> 13:21.890 resurrection would work. 13:21.890 --> 13:26.640 13:26.639 --> 13:28.379 I don't know, theology aside, 13:28.377 --> 13:32.097 I don't know what to say about the metaphysical questions. 13:32.100 --> 13:37.580 When I think about the tower case, I do find myself inclined 13:37.575 --> 13:42.395 to say, with van Inwagen, that's not the tower my son 13:42.401 --> 13:46.091 built. But when I think about the 13:46.089 --> 13:52.669 watch case, I find myself saying that is the very same watch. 13:52.669 --> 13:57.659 Now, all I can do is invite you to think about these two cases 13:57.660 --> 14:01.260 and ask yourself, what should we say here? 14:01.259 --> 14:05.279 Of course, for those people who think it really is the same 14:05.275 --> 14:06.655 tower, no problem. 14:06.659 --> 14:08.279 Then we say, the watch and the tower, 14:08.278 --> 14:10.258 in both cases, it's the very same object when 14:10.256 --> 14:11.196 it's reassembled. 14:11.200 --> 14:13.720 Reassemble the body, that'll be the very same body 14:13.724 --> 14:15.654 as well. For those people who say, 14:15.651 --> 14:18.131 "Yeah, van Inwagen was right about the tower, 14:18.134 --> 14:21.074 and the same thing would be true about the watch. 14:21.070 --> 14:25.060 The reassembled watch isn't the very same watch," then we have 14:25.056 --> 14:28.906 to say bodily resurrection would not be the very same 14:28.911 --> 14:32.941 body. So that wouldn't be me waking 14:32.944 --> 14:35.324 up on Judgment Day. 14:35.320 --> 14:39.660 The alternative is to try to find some relevant difference 14:39.659 --> 14:43.009 between the watch case and the tower case. 14:43.009 --> 14:47.769 Something that allows us to say that "well, when you reassemble 14:47.774 --> 14:50.314 the watch it is the same watch. 14:50.309 --> 14:54.049 When you reassemble the tower, it's not the same tower. 14:54.049 --> 14:57.189 Here's the explanation of why those two things work 14:57.190 --> 14:59.640 differently in the reassembly cases." 14:59.639 --> 15:01.819 And then of course, we'd have to further 15:01.816 --> 15:04.546 investigate whether when you reassemble a body, 15:04.549 --> 15:08.999 is it more like the watch case or is it more like the tower 15:09.002 --> 15:11.262 case? I just have to confess, 15:11.260 --> 15:15.450 I don't know what the best thing to say about these cases 15:15.451 --> 15:17.971 is. I find myself inclined to think 15:17.965 --> 15:20.025 reassembled watch, same watch. 15:20.029 --> 15:22.819 Reassembled tower, not same tower. 15:22.820 --> 15:24.370 Maybe there's a difference there. 15:24.370 --> 15:27.460 I don't have a good theory as to what the difference is. 15:27.460 --> 15:30.440 Since I don't have a good theory as to what the difference 15:30.440 --> 15:33.630 is, I'm not in a good position to decide whether a reassembled 15:33.630 --> 15:36.350 body would be the same body or a different body. 15:36.350 --> 15:41.070 I don't know. So there's metaphysical work to 15:41.066 --> 15:46.406 be done here by anybody who's at least interested in getting this 15:46.405 --> 15:49.905 theory of identity worked out properly. 15:49.909 --> 15:53.079 Still, at least the possibility that we could work this out is 15:53.081 --> 15:56.071 still there. So I suppose there's still at 15:56.072 --> 16:00.292 least the possibility that bodily resurrection would be 16:00.285 --> 16:05.195 coherent in such a way that it would still be the same body. 16:05.200 --> 16:09.530 So if we accept the body theory, could there be life 16:09.531 --> 16:12.111 after death? Could there be survival of the 16:12.113 --> 16:12.953 death of my body? 16:12.950 --> 16:16.590 Seems like, as far as I can tell, it's still a possibility, 16:16.592 --> 16:20.242 although there's some puzzles here that I don't know how to 16:20.235 --> 16:21.675 see my way through. 16:21.679 --> 16:26.209 Mind you, that's not to say that I myself do believe that 16:26.209 --> 16:30.499 there will be a Judgment Day, and on that day God will 16:30.496 --> 16:32.596 reassemble the bodies. 16:32.600 --> 16:35.380 But it at least seems like a coherent possibility. 16:35.380 --> 16:39.110 16:39.110 --> 16:44.400 Let's refine the body view. 16:44.399 --> 16:47.479 I've been suggesting that the key here, the idea of whether 16:47.475 --> 16:50.705 it's the same person or not, is whether it's the same body. 16:50.710 --> 16:54.560 But of course as we know in thinking about familiar objects, 16:54.562 --> 16:58.222 we don't need to have every single piece of an object, 16:58.220 --> 17:00.770 of an entity, stay the same to have the same 17:00.774 --> 17:03.484 thing. So I think I previously talked 17:03.477 --> 17:06.147 about the steering wheel in my car. 17:06.150 --> 17:09.270 Every time I drive the steering wheel in my car, 17:09.272 --> 17:10.802 I rub off some atoms. 17:10.800 --> 17:12.390 But that's okay. It's still the very same 17:12.385 --> 17:16.085 physical object. The steering wheel is--Having 17:16.085 --> 17:21.795 the same steering wheel is compatible with changing of a 17:21.804 --> 17:25.404 few pieces. The same thing is true for 17:25.403 --> 17:27.843 bodies, right? You get sunburned, 17:27.839 --> 17:30.909 your skin peels, you've lost some atoms in your 17:30.906 --> 17:32.776 body. It doesn't really matter. 17:32.780 --> 17:34.880 It's still the very same body. 17:34.880 --> 17:37.590 So if body is the key to personal identity, 17:37.585 --> 17:41.315 we don't have to worry about the fact that we're constantly 17:41.321 --> 17:43.191 gaining and losing atoms. 17:43.190 --> 17:47.650 Yes, question? Student: What about 17:47.651 --> 17:53.461 someone who loses a huge amount of weight? 17:53.460 --> 17:53.850 Professor Shelly Kagan: Good. 17:53.849 --> 17:56.799 The question was, "What about somebody who loses 17:56.803 --> 17:58.503 a huge amount of weight?" 17:58.500 --> 18:00.020 They feel different. 18:00.020 --> 18:01.570 People treat them different. 18:01.570 --> 18:02.960 What about that case? 18:02.960 --> 18:06.990 Well, I think if we're doing metaphysics, as opposed to 18:06.990 --> 18:11.490 psychology--Psychologically, we understand why losing weight 18:11.491 --> 18:16.161 might make a real difference as to how you feel about yourself. 18:16.160 --> 18:20.590 And we might even say, loosely, it's as though she's a 18:20.591 --> 18:22.181 whole new person. 18:22.180 --> 18:26.870 But strictly speaking, we don't think it is literally 18:26.867 --> 18:28.757 a whole new person. 18:28.759 --> 18:32.499 It's not as though we say, "Poor Linda died when she 18:32.500 --> 18:36.900 entered the spa. Or a week into the spa when she 18:36.897 --> 18:39.377 dropped those 50 pounds. 18:39.380 --> 18:43.020 Somebody else who remembers all of Linda's childhood, 18:43.019 --> 18:44.979 some imitator came along." 18:44.980 --> 18:46.670 We don't say "different person." 18:46.670 --> 18:49.960 We say "same person, lost a lot of weight." 18:49.960 --> 18:52.380 Now that's not a problem for the body view, 18:52.377 --> 18:54.737 because on the body view, the question is, 18:54.738 --> 18:56.118 is it the same body? 18:56.119 --> 18:59.779 And what we want to say is, of course, look, 18:59.777 --> 19:04.877 just like it's still your body even if you break your arm. 19:04.880 --> 19:08.460 Even though--It's still your body after you've eaten dinner, 19:08.456 --> 19:11.966 and so now some molecules have been absorbed into your body 19:11.971 --> 19:13.791 that weren't there before. 19:13.789 --> 19:18.629 It's still your body after you lose some molecules, 19:18.625 --> 19:21.135 even a lot of molecules. 19:21.140 --> 19:27.810 There can be changes in your body that are compatible with it 19:27.808 --> 19:30.918 still being the same body. 19:30.920 --> 19:35.230 Now, we might worry about the--Which changes? 19:35.230 --> 19:39.060 Are all the changes, it's certainly not as though 19:39.056 --> 19:40.726 any change will do. 19:40.730 --> 19:44.690 I mean, suppose what happens is Linda goes to bed and what we do 19:44.691 --> 19:48.721 in the middle of the night is we take away that body and put some 19:48.715 --> 19:51.195 new body there. Well that 100% change, 19:51.201 --> 19:52.671 that's clearly too much. 19:52.670 --> 19:55.840 19:55.839 --> 20:00.189 Change of some small percentage, from eating, 20:00.188 --> 20:03.598 not a problem. Change from a somewhat larger 20:03.599 --> 20:07.449 percentage of losing a fair bit of weight doesn't seem to be a 20:07.446 --> 20:11.406 problem. So which changes in bodies make 20:11.410 --> 20:17.530 for a different body and which changes in body make for the 20:17.528 --> 20:19.938 same body? And in particular, 20:19.942 --> 20:23.482 how should we run that if we're thinking about the body as the 20:23.477 --> 20:25.097 key to personal identity? 20:25.099 --> 20:29.469 I think if we have that question in front of our minds, 20:29.469 --> 20:33.919 we're going to want to say not all parts of the body are 20:33.919 --> 20:35.699 equally important. 20:35.700 --> 20:38.930 You lose a fair bit of weight, some fat from your gut, 20:38.926 --> 20:40.706 not a problem. Here's one of my favorite 20:40.714 --> 20:44.404 examples. In the Star Wars movies, 20:44.395 --> 20:52.915 Darth Vader whips out his light saber and slashes off the hand 20:52.923 --> 20:55.863 of Luke Skywalker. 20:55.860 --> 20:57.230 "Luke, I am your father." 20:57.230 --> 21:00.400 "No!" Then the hand goes, right? 21:00.400 --> 21:03.910 The very next scene--this has always amazed me--the very next 21:03.907 --> 21:07.587 scene, Luke's got an artificial hand that's been attached to his 21:07.590 --> 21:10.280 body and they never even mention it again. 21:10.280 --> 21:12.830 No one says, "Oh, poor Luke. 21:12.829 --> 21:18.399 He died when Darth Vader cut off the hand." 21:18.400 --> 21:24.110 It seems pretty clear that not all parts of the body matter. 21:24.109 --> 21:28.319 You can lose a hand and still survive. 21:28.319 --> 21:32.169 Same body, except now without a hand. 21:32.170 --> 21:37.320 Suppose Darth Vader had aimed a little higher and cut off Luke's 21:37.317 --> 21:39.677 entire arm. It would still be Luke. 21:39.680 --> 21:41.840 It would still be Luke's body. 21:41.839 --> 21:46.459 Suppose, even worse, Darth Vader slices off both 21:46.457 --> 21:48.517 arms and both legs. 21:48.520 --> 21:50.470 It would still be Luke. 21:50.470 --> 21:52.870 It would still be Luke's body, though now without arms and 21:52.874 --> 21:53.174 legs. 21:53.170 --> 21:56.290 21:56.289 --> 22:00.479 What part of the body, if any, is essential? 22:00.480 --> 22:03.050 Well here's a proposal. 22:03.049 --> 22:06.849 It seems to me we'd say something rather different if 22:06.846 --> 22:11.296 what happened was that what got destroyed was Luke's brain. 22:11.299 --> 22:15.379 Suppose that Darth Vader uses the force--the dark side of the 22:15.383 --> 22:19.403 force of course--Darth Vader uses the dark side of the force 22:19.399 --> 22:23.099 to destroy, to turn into pea soup, 22:23.098 --> 22:26.018 Luke Skywalker's brain. 22:26.019 --> 22:28.729 Now I think we might want to say, "Well look, 22:28.726 --> 22:32.936 no more Luke." And if what happens is they 22:32.936 --> 22:39.386 drag out some replacement brain, it's still not Luke. 22:39.390 --> 22:45.120 At least, that's a possible version of the body view. 22:45.119 --> 22:48.619 According to this version, which I take to be the most 22:48.617 --> 22:51.717 promising, the best version of the body view, 22:51.720 --> 22:54.440 the crucial question in thinking about personal identity 22:54.436 --> 22:57.096 is whether it's the same body--but not all parts of the 22:57.104 --> 22:58.294 body matter equally. 22:58.289 --> 23:02.649 The most important part of the body is the brain. 23:02.650 --> 23:03.960 Well, why the brain? 23:03.960 --> 23:07.670 No surprise there, because of course the brain is 23:07.674 --> 23:11.544 the part, we now know, the brain is the part of the 23:11.543 --> 23:15.183 body that is the house of your personality, 23:15.180 --> 23:17.200 your beliefs, your desires, 23:17.196 --> 23:21.536 your fears, your ambitions, your goals, your memories. 23:21.540 --> 23:24.870 That's all housed in the brain. 23:24.869 --> 23:31.019 And so that's the part of the brain that's the key part of the 23:31.016 --> 23:35.446 body for the purpose of personal identity. 23:35.450 --> 23:39.580 That's what I'm inclined to think is the best version of the 23:39.579 --> 23:40.419 body view. 23:40.420 --> 23:45.560 23:45.559 --> 23:51.679 We find examples of this thought, that the brain is the 23:51.680 --> 23:54.060 key, in odd places. 23:54.059 --> 23:56.539 So let me actually share one with you. 23:56.539 --> 24:00.499 This was something from the Internet that my brother sent to 24:00.498 --> 24:01.838 me some years ago. 24:01.839 --> 24:06.949 It purports to be from a transcript from an actual trial 24:06.948 --> 24:11.498 in which a lawyer's cross examining the doctor. 24:11.500 --> 24:14.400 And you'll see. I don't actually know whether 24:14.397 --> 24:16.477 it's true or not, whether it's just somebody made 24:16.479 --> 24:18.679 it up. But it purports to be true. 24:18.680 --> 24:22.150 Q: Doctor, before you performed the 24:22.149 --> 24:24.879 autopsy, did you check for a pulse? 24:24.880 --> 24:28.790 A: No. Q: Did you check for 24:28.790 --> 24:31.920 blood pressure? A: No. 24:31.920 --> 24:34.410 Q: Did you check for breathing? 24:34.410 --> 24:38.760 A: No. Q: So then it is 24:38.757 --> 24:43.607 possible that the patient was alive when you began the 24:43.612 --> 24:46.972 autopsy? A: No. 24:46.970 --> 24:51.280 Q: How can you be so sure, doctor? 24:51.279 --> 24:58.019 A: Because his brain was sitting on my desk in a jar. 24:58.019 --> 25:02.589 Q: But could the patient have still been alive 25:02.591 --> 25:06.721 nevertheless? A: It is possible that 25:06.722 --> 25:12.642 he could have been alive and practicing law somewhere. 25:12.640 --> 25:17.910 The point--The reason that this is funny, other than of course 25:17.911 --> 25:21.631 the obvious moral, which is that lawyers are 25:21.627 --> 25:24.217 morons, is that of course. 25:24.220 --> 25:26.210 Why is it so clear the lawyer's got to be a moron? 25:26.210 --> 25:29.120 Because of course we think, look, lose a hand, 25:29.117 --> 25:31.117 the guy could still be alive. 25:31.120 --> 25:32.810 Lose an arm, lose a leg. 25:32.809 --> 25:36.939 Lose the brain, he's not alive. 25:36.940 --> 25:40.420 So again this is, this is hardly philosophical 25:40.416 --> 25:44.966 proof, but it shows that we're drawn to the thought that the 25:44.974 --> 25:47.914 key part of the body is the brain. 25:47.910 --> 25:50.400 Now, think about what the implication of holding that 25:50.395 --> 25:54.065 view. Suppose we adopt that version 25:54.074 --> 25:56.154 of the body view. 25:56.150 --> 26:04.260 If I get a liver transplant, so here I am and we take out my 26:04.259 --> 26:09.619 liver and we put Jones' liver inside. 26:09.620 --> 26:12.020 I've gotten a liver transplant. 26:12.020 --> 26:17.430 It's still me. Suppose we rip out my heart and 26:17.430 --> 26:20.240 put Jones' heart in here. 26:20.240 --> 26:23.080 I've gotten a heart transplant. 26:23.080 --> 26:28.760 It's still me. Suppose we rip out my lungs and 26:28.758 --> 26:31.058 put in Jones' lungs. 26:31.060 --> 26:34.250 I've gotten a lung transplant. 26:34.250 --> 26:39.580 It's still me. Suppose we rip out my brain, 26:39.584 --> 26:42.284 put in Jones' brain. 26:42.279 --> 26:45.729 Have I gotten a brain transplant? 26:45.730 --> 26:50.270 No. What's happened is that 26:50.269 --> 26:55.659 Jones has gotten a body transplant. 26:55.660 --> 27:00.200 Or, as we might put it, a torso transplant. 27:00.200 --> 27:04.710 If we accept this version of the body theory, 27:04.705 --> 27:10.745 we say the crucial part of the body for personal identity is 27:10.747 --> 27:13.407 not sameness of torso. 27:13.410 --> 27:19.610 The crucial part of the body is sameness of brain. 27:19.609 --> 27:23.209 Just like "follow the soul" was the answer if we believe in the 27:23.208 --> 27:25.238 soul theory of personal identity, 27:25.240 --> 27:30.760 if we believe in the brain version of the body theory of 27:30.761 --> 27:34.241 personal identity, same person or not? 27:34.240 --> 27:37.770 Follow the brain. 27:37.770 --> 27:40.480 Same brain, same person. 27:40.480 --> 27:44.800 Different brain, different person. 27:44.799 --> 27:48.469 As I've now been saying several times, I think that's the best 27:48.473 --> 27:51.853 version of the body view, although not all body theorists 27:51.846 --> 27:54.536 believe that. As you know from reading your 27:54.539 --> 27:57.709 Perry, the assigned reading, his Dialogue on Personal 27:57.707 --> 28:01.887 Identity and Immortality, the heroine of that story, 28:01.887 --> 28:07.097 Gertrude--Gertrude actually thinks the key part of the body 28:07.101 --> 28:10.581 is the torso. Follow the torso, 28:10.575 --> 28:12.845 follow the person. 28:12.850 --> 28:14.650 That's what she thinks. 28:14.650 --> 28:15.920 I'm inclined to say, no. 28:15.920 --> 28:18.780 In those moods, when I accept the body theory, 28:18.783 --> 28:21.713 I'm inclined to think, no, follow the brain. 28:21.710 --> 28:25.580 28:25.579 --> 28:29.509 Gertrude would presumably say you get a brain transplant, 28:29.514 --> 28:33.594 you got a brain transplant, because it's the same torso. 28:33.589 --> 28:36.709 I want to say, as a fan of the brain theory, 28:36.705 --> 28:40.465 you get a brain transplant, what's really happened is 28:40.472 --> 28:43.952 somebody else has gotten a torso transplant. 28:43.950 --> 28:46.270 Follow the brain. 28:46.270 --> 28:47.790 How much of the brain? 28:47.790 --> 28:50.900 Do we need all of the brain? 28:50.900 --> 28:56.560 Well, just like we didn't have to follow the parts of the body 28:56.562 --> 29:01.392 that aren't essential for housing the personality, 29:01.390 --> 29:07.160 we might ask ourselves, "Do we need all of the brain to 29:07.159 --> 29:09.829 house the personality?" 29:09.829 --> 29:14.359 Research suggests that there's a fair bit of redundancy in the 29:14.356 --> 29:18.436 brain. You can lose portions of the 29:18.444 --> 29:25.684 brain and still have a perfectly functioning, P-functioning 29:25.682 --> 29:29.172 person. Some of you may know that there 29:29.165 --> 29:33.415 have been experiments in which, for one reason or the other, 29:33.421 --> 29:37.101 the two halves of the brain have been separated. 29:37.099 --> 29:42.659 And you often end up there with, well, something closer to 29:42.664 --> 29:46.964 two persons being housed within one skull, 29:46.960 --> 29:49.930 because they can often still communicate in various ways. 29:49.930 --> 29:51.480 We don't quite get that. 29:51.480 --> 29:55.110 I gather that the best research suggests we don't really have 29:55.110 --> 29:57.470 complete redundancy with hemispheres. 29:57.470 --> 29:59.480 But suppose that we did. 29:59.480 --> 30:02.090 Let's be science-fictiony. 30:02.089 --> 30:05.879 Suppose that, as a kind of backup security, 30:05.875 --> 30:10.915 what evolution has done is produced so much redundancy in 30:10.922 --> 30:16.152 the brain that either half of the brain would suffice. 30:16.150 --> 30:19.100 All right, so think about our brain transplant example. 30:19.099 --> 30:23.809 So there's an accident with Jones and Smith. 30:23.810 --> 30:29.230 Jones' torso gets destroyed. 30:29.230 --> 30:31.950 His brain is fine. 30:31.950 --> 30:35.080 Smith's brain has gotten destroyed. 30:35.080 --> 30:37.350 His torso is fine. 30:37.350 --> 30:42.400 We take Jones' brain; we put it in Smith's torso. 30:42.400 --> 30:45.210 We hook up all the wires, as it were. 30:45.210 --> 30:46.570 The thing wakes up. 30:46.570 --> 30:50.990 Who is that? Jones' brain, Smith's torso. 30:50.990 --> 30:52.160 Follow the brain. 30:52.160 --> 30:56.050 That's Jones that woke up. 30:56.050 --> 30:58.740 Version two. Horrible accident. 30:58.740 --> 31:03.400 Jones' torso has been destroyed and the left half of his brain 31:03.396 --> 31:04.996 has been destroyed. 31:05.000 --> 31:09.730 But the right half of his brain is still there. 31:09.730 --> 31:13.830 Smith's torso is fine, but his entire brain has been 31:13.826 --> 31:17.136 destroyed. We take the right half of 31:17.137 --> 31:20.797 Jones' brain, put it into Smith's torso, 31:20.799 --> 31:26.339 hook up all the wires the right way, the thing wakes up. 31:26.340 --> 31:29.810 Who is it? It's Jones. 31:29.809 --> 31:33.619 Follow the brain, and more particularly, 31:33.615 --> 31:39.265 follow however much of the brain it takes to have enough of 31:39.274 --> 31:44.254 the brain there to still give you the memories, 31:44.250 --> 31:47.390 beliefs, desires, and so forth and so on. 31:47.390 --> 31:50.460 If it were true--it probably isn't true, but if it were 31:50.455 --> 31:53.795 true--that half of the brain was enough, then half the brain 31:53.804 --> 31:56.604 would be enough. That would be Jones that woke 31:56.600 --> 31:58.070 up. Question? 31:58.069 --> 32:03.019 Student: [inaudible] Professor Shelly Kagan: 32:03.015 --> 32:04.815 Great. The question was, 32:04.816 --> 32:07.746 "On this theory, what do we say about the case 32:07.745 --> 32:10.865 where we take the two halves of Jones' brain, 32:10.869 --> 32:13.339 split them, put them in two different torsos. 32:13.340 --> 32:15.010 They both wake up. 32:15.010 --> 32:17.110 Would they both be Jones?" 32:17.110 --> 32:19.720 That's a wonderful question. 32:19.720 --> 32:22.530 It's a wonderful case to think about and, indeed, 32:22.534 --> 32:24.414 I am going to come back to it. 32:24.410 --> 32:28.610 But I just want to bracket it for the time being. 32:28.609 --> 32:33.579 But it's a great question to keep in mind as you think about 32:33.579 --> 32:36.779 the plausibility of the body theory. 32:36.779 --> 32:41.779 All right, so I'm inclined to think that the best version of 32:41.784 --> 32:46.284 the body theory has to do with following the brain. 32:46.279 --> 32:48.959 So one thing that a physicalist, who does not 32:48.959 --> 32:51.699 believe in souls, one thing that a physicalist 32:51.700 --> 32:54.140 could say is, "What's the key to personal 32:54.136 --> 32:56.156 identity? The body. 32:56.160 --> 32:59.190 Sameness of body." 32:59.190 --> 33:03.920 And then I'm inclined to think the best version of the body 33:03.920 --> 33:05.960 view is the brain view. 33:05.960 --> 33:08.820 So that's something that a physicalist can say. 33:08.819 --> 33:11.129 And for that matter, it's something that a soul, 33:11.128 --> 33:13.708 somebody who believes in souls, could say as well: 33:13.708 --> 33:16.578 even though there are souls, that may not be the key to 33:16.582 --> 33:17.702 personal identity. 33:17.700 --> 33:23.400 Maybe sameness of body is the key to personal identity. 33:23.400 --> 33:26.520 That's something a physicalist or dualist can say. 33:26.519 --> 33:30.209 But, and this is not--to make good on a promissory note I 33:30.210 --> 33:32.720 offered earlier, it's not the only view 33:32.715 --> 33:38.195 available to physicalists or, for that matter, dualists. 33:38.200 --> 33:43.060 Even if there are no souls, we don't have to say that the 33:43.058 --> 33:47.828 key to personal identity is the sameness of the body. 33:47.829 --> 33:54.799 We could instead say the key to personal identity is the 33:54.798 --> 33:58.598 sameness of the personality. 33:58.599 --> 34:03.479 After all, go back to the Lockean worries about the soul 34:03.478 --> 34:06.138 theory of personal identity. 34:06.140 --> 34:11.150 It seemed very hard to believe that it isn't the same person 34:11.151 --> 34:15.741 when the memories and beliefs and desires and goals and 34:15.737 --> 34:19.217 ambitions and fears are all the same, 34:19.219 --> 34:22.159 even if a soul is constantly changing. 34:22.159 --> 34:24.369 It seems as though we wanted to say same person. 34:24.370 --> 34:26.620 Why? Roughly speaking, 34:26.621 --> 34:29.591 because it's the same personality. 34:29.590 --> 34:33.440 And with the body view, when I started arguing a few 34:33.437 --> 34:37.737 moments ago that the best version of the body view was the 34:37.738 --> 34:40.368 brain view, why did that seem plausible? 34:40.369 --> 34:44.689 Why didn't we say that Luke died when he lost his wrist? 34:44.690 --> 34:48.860 Because the brain, after all, was the part of the 34:48.859 --> 34:51.899 body that houses the personality. 34:51.900 --> 34:53.980 Enough of the brain was good enough, I said. 34:53.980 --> 34:56.490 What counts as good enough? 34:56.490 --> 34:58.910 Enough to keep the personality. 34:58.909 --> 35:03.339 Well, if what we think is really important here is the 35:03.342 --> 35:08.532 personality, why don't we just say the key to personal identity 35:08.526 --> 35:10.446 is the personality? 35:10.449 --> 35:17.649 Let's just say it's me, provided that there's somebody 35:17.646 --> 35:23.346 who's got the same set of beliefs, desires, 35:23.349 --> 35:28.509 goals, memories, ambitions, fears. 35:28.510 --> 35:34.910 To coin a word, the same "personality." 35:34.909 --> 35:40.689 So the secret to personal identity on this new proposal 35:40.691 --> 35:46.581 isn't sameness of body, it's sameness of personality. 35:46.580 --> 35:53.680 35:53.679 --> 35:59.239 Now, it's important to bear in mind that this view is perfectly 35:59.241 --> 36:02.651 compatible with being a physicalist. 36:02.650 --> 36:07.100 After all, we're not saying that in order to have 36:07.100 --> 36:12.200 personalities you need to have something nonphysical. 36:12.199 --> 36:16.719 As physicalists, we can still say that the basis 36:16.717 --> 36:22.677 of personality is that there are bodies that are functioning in 36:22.676 --> 36:25.776 certain ways. But for all that, 36:25.776 --> 36:30.176 the key to the same person could have to do with the 36:30.176 --> 36:34.486 personality rather than the sameness of bodies. 36:34.489 --> 36:40.319 Of course, normally the way you get the same personality is by 36:40.321 --> 36:42.521 having the same body. 36:42.519 --> 36:46.449 Still, if we ask, "What's doing the metaphysical 36:46.447 --> 36:50.477 work here? What's the key to being the 36:50.479 --> 36:54.059 same person?" we can say sameness of body 36:54.064 --> 36:57.874 gave us the same personality, but it was sameness of 36:57.869 --> 37:01.749 personality that made it be the very same person. 37:01.750 --> 37:05.520 37:05.519 --> 37:09.519 Could there be some way to get sameness of personality while 37:09.524 --> 37:11.564 not having sameness of body? 37:11.560 --> 37:15.120 Maybe. Suppose that we had some 37:15.117 --> 37:17.467 disease. The doctor tells me the 37:17.472 --> 37:21.252 horrible news that I'm going to have some disease that's going 37:21.246 --> 37:24.026 to eventually turn my brain into pea soup. 37:24.030 --> 37:26.920 But luckily, just before it does it, 37:26.916 --> 37:31.286 they can take all of my personality and put it into an 37:31.288 --> 37:34.008 artificial replacement brain. 37:34.010 --> 37:36.120 So there'll be --just like you can have artificial hearts, 37:36.119 --> 37:38.989 artificial livers, you can have artificial brains, 37:38.985 --> 37:42.545 which will get imprinted with the same personality. 37:42.550 --> 37:44.480 Same memory, same beliefs, 37:44.475 --> 37:47.475 same desires, same fears, same goals. 37:47.480 --> 37:48.860 We obviously can't do that. 37:48.860 --> 37:51.340 This is a science fiction story. 37:51.340 --> 37:54.610 But at least it allows you to see how the body and the 37:54.614 --> 37:56.534 personality could come apart. 37:56.530 --> 38:00.450 And so we could have same personality without literally 38:00.446 --> 38:03.866 the same brain. If personality is the key to 38:03.868 --> 38:07.228 personal identity, that would still be me. 38:07.230 --> 38:09.390 Hold off again for a few minutes, at least, 38:09.386 --> 38:11.536 on the question, "So what should we believe 38:11.543 --> 38:13.703 here, the body, the personality view?" 38:13.699 --> 38:19.059 Let's try to refine the personality theory. 38:19.059 --> 38:23.289 So again, the point I was just emphasizing was even if we 38:23.285 --> 38:27.885 accept the personality theory, this doesn't threaten our being 38:27.887 --> 38:30.467 physicalists. We can still say the reason 38:30.471 --> 38:33.171 that we've got the same personality in the normal case, 38:33.170 --> 38:36.350 is there's some physical explanation of what houses the 38:36.346 --> 38:38.696 personality. But for all that, 38:38.702 --> 38:43.212 the key to personal identity is same personality. 38:43.210 --> 38:46.780 Notice, by the way, that somebody who believes in 38:46.781 --> 38:51.021 souls could also accept the personality theory of personal 38:51.022 --> 38:54.712 identity. Locke believed in souls. 38:54.710 --> 38:58.350 He just didn't think they were the key to personal identity. 38:58.350 --> 39:00.000 So you might think, "Oh no. 39:00.000 --> 39:03.330 The physicalist is wrong when the physicalist says that 39:03.325 --> 39:05.905 personality--memory, belief, consciousness, 39:05.911 --> 39:08.991 what have you--is housed or based in the body. 39:08.989 --> 39:11.789 It's based in an immaterial soul." 39:11.790 --> 39:14.180 Dualists could say that. 39:14.179 --> 39:18.669 And yet, for all that, the dualist could consistently 39:18.671 --> 39:23.941 say, "Still, same soul is not the key to personal identity. 39:23.940 --> 39:28.480 Same personality is the key to personal identity. 39:28.480 --> 39:32.650 If God replaces my soul every 10 minutes, as long as He does 39:32.650 --> 39:37.030 it in such a way as to imprint the very same personality on the 39:37.033 --> 39:39.123 soul, it doesn't matter any more than 39:39.124 --> 39:41.804 it didn't matter whether or not some of my body parts were 39:41.799 --> 39:44.879 changing." So the personality theory of 39:44.878 --> 39:49.728 personal identity can be accepted by physicalists and it 39:49.727 --> 39:52.457 can be accepted by dualists. 39:52.460 --> 39:57.590 39:57.590 --> 40:02.440 So, just to keep score, right now we've got three basic 40:02.439 --> 40:06.479 theories of personal identity on the table. 40:06.480 --> 40:09.650 The soul theory, the key to personal identity is 40:09.650 --> 40:11.730 the same soul. The body theory, 40:11.725 --> 40:14.645 the key to personal identity is the same body. 40:14.650 --> 40:17.390 Where the best version, I think, is the brain version 40:17.392 --> 40:18.502 of the body theory. 40:18.500 --> 40:22.820 And the personality theory, the key to personal identity is 40:22.815 --> 40:25.415 having the very same personality. 40:25.420 --> 40:30.080 40:30.079 --> 40:33.749 Well again, we've got to be careful about refining this. 40:33.750 --> 40:37.340 Just like we all agreed, I suppose, that you can have 40:37.340 --> 40:40.660 the very same body, even though some of the parts 40:40.655 --> 40:43.185 come and go, atoms get added, 40:43.192 --> 40:45.792 other atoms get knocked off. 40:45.789 --> 40:51.639 We can say, we'd better say, that you can have the very same 40:51.639 --> 40:57.489 personality even if some of the elements in your personality 40:57.489 --> 41:00.649 change. After all, we defined the 41:00.649 --> 41:05.699 personality in terms of it being a set of beliefs and memories 41:05.697 --> 41:09.667 and desires and goals and fears and so forth. 41:09.670 --> 41:12.910 But those things are constantly changing. 41:12.909 --> 41:17.919 I have all sorts of memories now that I didn't have when I 41:17.919 --> 41:19.709 was 10. I have memories of getting 41:19.712 --> 41:20.562 married, for example. 41:20.560 --> 41:23.710 I wasn't married when I was 10. 41:23.710 --> 41:27.860 So does the personality theorist have to say, 41:27.855 --> 41:30.865 "Uh-oh, different personality. 41:30.870 --> 41:33.740 That kid no longer exists. 41:33.739 --> 41:37.519 That person died, got married and the memories 41:37.518 --> 41:39.428 died." If we say that, 41:39.425 --> 41:42.055 we have very, very short lives. 41:42.059 --> 41:45.079 Because after all, right now I've got some 41:45.079 --> 41:48.319 memories that I didn't have two hours ago. 41:48.320 --> 41:54.170 I have some memories I didn't have 20 minutes ago. 41:54.170 --> 41:59.440 If every time you got a new memory you had a new personality 41:59.444 --> 42:05.084 and the personality theory said having the very same personality 42:05.076 --> 42:09.676 was the key to survival, then none of us survive more 42:09.679 --> 42:11.179 than a few seconds. 42:11.179 --> 42:16.409 Well, the answer presumably is going to be that the best 42:16.412 --> 42:21.832 version of the personality theory doesn't require item for 42:21.834 --> 42:25.454 item having the very same beliefs, 42:25.450 --> 42:27.470 memories, desires, and so forth. 42:27.469 --> 42:35.099 But instead requires enough gradual overlap. 42:35.099 --> 42:39.319 Your personality can change and evolve over time. 42:39.320 --> 42:42.500 So here I am as a 10 year old child. 42:42.500 --> 42:45.100 I've got certain desires, certain memories. 42:45.099 --> 42:48.039 As the year goes by, I get some new memories. 42:48.040 --> 42:50.660 I lose some of my goals. 42:50.659 --> 42:54.519 I no longer--When I was 10, when I grew up I wanted to be a 42:54.521 --> 42:57.471 trash collector. That was my first chosen 42:57.466 --> 43:00.326 profession. At some point I gave up that 43:00.331 --> 43:02.361 desire. I didn't want to be a trash 43:02.355 --> 43:03.375 collector anymore. 43:03.380 --> 43:05.220 I wanted to be, I kid you not, 43:05.222 --> 43:08.402 I wanted to be a logician when I was a teenager. 43:08.400 --> 43:11.270 I wanted to study symbolic logic. 43:11.269 --> 43:13.429 So at a certain point I gave that up. 43:13.429 --> 43:17.709 So my memories, my desires were changing, 43:17.714 --> 43:21.254 but they all changed gradually. 43:21.250 --> 43:23.100 I lost some old memories. 43:23.099 --> 43:25.849 I don't remember everything I knew or remembered when I was 43:25.852 --> 43:27.112 10. When I was 10, 43:27.107 --> 43:30.377 I had pretty vivid memories of kindergarten. 43:30.380 --> 43:35.160 Now I have very sketchy memories of kindergarten. 43:35.160 --> 43:37.570 Still, it wasn't abrupt. 43:37.570 --> 43:41.230 It was gradual. There was this slow evolution 43:41.231 --> 43:42.881 of the personality. 43:42.880 --> 43:46.420 And so when the personality theorist says the key to 43:46.417 --> 43:49.467 personal identity is the same personality, 43:49.469 --> 43:54.369 they don't' mean literally the very same set of beliefs and 43:54.374 --> 43:56.964 desires. They mean, rather, 43:56.958 --> 44:00.628 the same slowly evolving personality. 44:00.630 --> 44:04.230 44:04.230 --> 44:05.530 Here's an analogy. 44:05.530 --> 44:12.770 Suppose I had a rope that stretched from that end of the 44:12.769 --> 44:19.349 room all the way across to this end of the room. 44:19.349 --> 44:24.379 Very same rope at that end as this end. 44:24.380 --> 44:25.460 What makes up a rope? 44:25.460 --> 44:28.830 Well as you know, ropes are basically bundles of 44:28.827 --> 44:32.977 fibers, very thin fibers that have been woven together in a 44:32.983 --> 44:35.943 certain way. But the interesting thing is 44:35.941 --> 44:39.371 the fibers themselves aren't actually all that long. 44:39.369 --> 44:42.959 They might be a couple of inches or at most a foot or so. 44:42.960 --> 44:49.120 And so no single fiber stretches all the way across the 44:49.121 --> 44:52.521 room. Or even if some fibers did, 44:52.518 --> 44:55.018 most of the fibers don't. 44:55.019 --> 44:57.549 Does that force us to say, "Ah, so it's not the very same 44:57.548 --> 44:59.308 rope at the end as at the beginning"? 44:59.310 --> 45:01.600 No. We don't have to say that at 45:01.604 --> 45:03.844 all. What we want to say is, 45:03.835 --> 45:08.125 "It's the same rope as long as there's this pattern of 45:08.134 --> 45:10.004 overlapping fibers." 45:10.000 --> 45:13.180 Certain fibers end, but most of the fibers are 45:13.181 --> 45:15.871 continuing. Some new fibers get introduced. 45:15.870 --> 45:17.570 They continue for a while. 45:17.570 --> 45:20.630 Eventually maybe those fibers end, but some new fibers have 45:20.633 --> 45:22.433 been introduced in the meantime. 45:22.430 --> 45:25.350 As long as it's not abrupt. 45:25.349 --> 45:30.199 Imagine I take my scissors and cut out a foot in the middle. 45:30.199 --> 45:33.859 Then we'd say there isn't the right kind of pattern of overlap 45:33.860 --> 45:36.360 and continuity. Now we really do have two 45:36.364 --> 45:38.624 ropes--one rope here, one rope there. 45:38.619 --> 45:41.619 But if, in contrast, there is the right kind of 45:41.615 --> 45:43.955 pattern of overlap and continuity, 45:43.960 --> 45:48.740 same rope, even though, even if no single fiber makes 45:48.742 --> 45:50.952 it all the way across. 45:50.949 --> 45:56.149 Something analogous needs to be said by the personality 45:56.150 --> 45:59.700 theorist. Even if I have few or no 45:59.704 --> 46:05.424 memories identical to the ones that I had when I was 10, 46:05.420 --> 46:09.840 that's okay. We can still say it's the same 46:09.843 --> 46:15.673 personality, the same evolving personality, so long as there's 46:15.666 --> 46:19.386 a pattern of overlap and continuity. 46:19.389 --> 46:22.779 New memories get added, some memories get lost. 46:22.780 --> 46:26.120 New goals get added, some goals get lost. 46:26.119 --> 46:29.129 New beliefs get added, some beliefs get lost. 46:29.130 --> 46:33.770 There might be few beliefs, desires, goals that made it all 46:33.769 --> 46:36.869 the way through. But as long as there's the 46:36.871 --> 46:40.451 right kind of overlap and continuity, same personality. 46:40.450 --> 46:42.950 All right, so what have we got? 46:42.949 --> 46:48.529 Three views--soul view, body view, personality view. 46:48.530 --> 46:52.890 Three rival theories about the key to personal identity. 46:52.890 --> 46:56.410 Now, which of these is right? 46:56.409 --> 46:59.319 Well, I don't myself believe in souls, it's hardly going to 46:59.321 --> 47:02.231 surprise you to learn that I don't think the soul theory of 47:02.233 --> 47:03.793 personal identity is right. 47:03.789 --> 47:09.039 For me, the choice boils down to the choice between the body 47:09.039 --> 47:14.019 theory of personal identity and the personality theory of 47:14.022 --> 47:15.982 personal identity. 47:15.980 --> 47:19.200 Of course, in real life, they go hand in hand. 47:19.199 --> 47:24.569 In ordinary cases at least, same body, same personality. 47:24.570 --> 47:27.350 Both theories are going to say it's the very same person. 47:27.349 --> 47:29.799 And if you believe in souls, you are likely to think, 47:29.798 --> 47:30.738 same soul as well. 47:30.739 --> 47:33.829 In ordinary cases, you have the same soul, 47:33.829 --> 47:37.069 same body, same personality, same person. 47:37.070 --> 47:41.050 To think about which one of these is the key to personal 47:41.046 --> 47:44.006 identity, we need to think about cases, 47:44.010 --> 47:47.660 maybe somewhat fantastical, science-fictiony, 47:47.660 --> 47:49.900 in which they come apart. 47:49.900 --> 47:56.020 Cases in which bodies and personalities go their own ways, 47:56.023 --> 48:00.423 as it were. So that's what I'm going to do. 48:00.420 --> 48:10.240 I'm going to tell you a story in which your body ends up one 48:10.237 --> 48:18.887 place and your personality ends up someplace else. 48:18.889 --> 48:24.779 And I'm going to invite you to think about which of these two 48:24.777 --> 48:27.817 resulting end products is me. 48:27.820 --> 48:32.760 If you could figure out which one's you, that would tell you 48:32.759 --> 48:37.359 whether you think the body theory is the right theory or 48:37.364 --> 48:41.304 the personality theory is the right theory. 48:41.300 --> 48:45.610 Now, what's going to be our guide? 48:45.610 --> 48:49.710 I'm going to, rather gruesomely--not in real 48:49.707 --> 48:54.847 life, a science fiction story--I'm going to torture one 48:54.852 --> 48:57.522 of the two end products. 48:57.519 --> 49:03.139 I'm going to ask you, "Which one do you want to be 49:03.142 --> 49:06.822 tortured?" Or to put the point more 49:06.822 --> 49:11.812 properly, which one do you want to not be tortured? 49:11.809 --> 49:16.249 Because I'm going to assume, I'm going to take it, 49:16.248 --> 49:21.138 that it's important to you that you not be tortured. 49:21.139 --> 49:26.399 So by seeing who you want to keep safe, this will help you 49:26.396 --> 49:29.436 see which one you think is you. 49:29.440 --> 49:33.510 49:33.510 --> 49:35.920 Of course, I've got to be sure that you're thinking about this 49:35.919 --> 49:36.669 in the right way. 49:36.670 --> 49:40.490 Like some of you are probably good, moral individuals and you 49:40.488 --> 49:42.778 don't want anybody to be tortured. 49:42.780 --> 49:45.070 I say, "Ah, I'm about to torture Linda over there." 49:45.070 --> 49:45.910 You say, "No, no. 49:45.910 --> 49:48.630 Don't torture Linda." 49:48.630 --> 49:52.090 Still, if I were to say to you, "I'm about to torture you." 49:52.090 --> 49:53.100 You'd say, "No, no! 49:53.100 --> 49:54.800 Don't torture me!" 49:54.800 --> 49:57.800 and there'd be some extra little something when you said 49:57.797 --> 50:01.447 that, right? So I want to invite you to keep 50:01.449 --> 50:07.229 that extra little something in mind when we tell the stories, 50:07.230 --> 50:10.010 which we won't get to until next time, when we tell the 50:10.012 --> 50:11.612 stories next time, and I say, 50:11.610 --> 50:13.680 "Okay, who do you want to be tortured, this person or that 50:13.677 --> 50:15.307 person?" The question is, 50:15.309 --> 50:19.439 from that special egoistic perspective that we're all 50:19.436 --> 50:22.686 familiar with, which is the one you really 50:22.690 --> 50:26.500 care about? That's going to be our guide to 50:26.504 --> 50:30.284 deciding what's the key to personal identity. 50:30.280 --> 50:33.400 But to hear the stories, you've got to come back next 50:33.400 --> 50:34.000 lecture.