WEBVTT 00:01.000 --> 00:04.520 Professor Shelly Kagan: Let me start by reviewing the 00:04.522 --> 00:07.212 problem that we were considering last week. 00:07.210 --> 00:10.710 We were raising a difficulty for the personality theory of 00:10.711 --> 00:14.461 personal identity according to which the key to being the same 00:14.458 --> 00:17.098 person is having the very same ongoing, 00:17.100 --> 00:19.180 evolving personality. 00:19.180 --> 00:22.920 And the difficulty was basically the problem of 00:22.921 --> 00:25.911 duplication. That it seemed as though we 00:25.905 --> 00:30.065 could have more than one--call it an individual--more than one 00:30.073 --> 00:32.543 body, that had the very same set of 00:32.535 --> 00:34.645 memories, beliefs and so forth. 00:34.650 --> 00:37.130 And that we have to ask ourselves, "Well, 00:37.130 --> 00:40.540 what should the personality theory say about a case like 00:40.540 --> 00:43.730 that?" So imagine that over the 00:43.728 --> 00:48.538 weekend, the mad scientist copied my memories, 00:48.543 --> 00:51.123 beliefs, desires, fears, 00:51.120 --> 00:55.420 ambitions, goals, intentions and imprinted that 00:55.415 --> 00:58.025 on somebody else's brain. 00:58.030 --> 01:00.960 They did it last night at midnight. 01:00.960 --> 01:05.450 This morning, we woke up. 01:05.450 --> 01:08.830 And we have to ask ourselves, "Who's Shelly Kagan? 01:08.829 --> 01:12.399 Who's the person that was lecturing to you last week?" 01:12.400 --> 01:17.110 Well, it doesn't seem plausible in terms of the personality 01:17.106 --> 01:20.836 theory to say that he's Shelly Kagan, 01:20.840 --> 01:24.650 and the one here today--Suppose the other one's in Michigan. 01:24.650 --> 01:28.170 If the one in Michigan's Shelly Kagan but this one's not--After 01:28.168 --> 01:31.058 all, although it's true that he's got Shelly Kagan's 01:31.062 --> 01:33.072 memories, he woke up thinking he was 01:33.067 --> 01:35.157 Shelly Kagan, just like I woke up thinking I 01:35.164 --> 01:36.144 was Shelly Kagan. 01:36.140 --> 01:38.970 He woke up thinking about what he was going to lecture on in 01:38.969 --> 01:41.989 class today, just like I woke up thinking about what I was going 01:41.991 --> 01:43.431 to lecture in class today. 01:43.430 --> 01:46.060 He remembered last week's lecture just like I remembered 01:46.058 --> 01:47.108 last week's lecture. 01:47.110 --> 01:51.670 Well, no clear reason to say--for the personality theory 01:51.669 --> 01:55.399 to say--that he's Shelly Kagan and I'm not. 01:55.400 --> 01:58.600 After all, I've got the very same set of memories, 01:58.597 --> 02:00.617 beliefs, desires that he has. 02:00.620 --> 02:03.090 But equally true, and more surprisingly, 02:03.086 --> 02:05.866 from the personality theory point of view, 02:05.870 --> 02:08.940 there's no reason to say that I'm Shelly Kagan and 02:08.942 --> 02:12.402 he's not. After all, he's got all the 02:12.396 --> 02:16.596 same memories, beliefs and desires that I do. 02:16.599 --> 02:19.679 It doesn't seem plausible to say we're both Shelly 02:19.681 --> 02:23.041 Kagan, because now we'd have to then say Shelly Kagan's in two 02:23.039 --> 02:24.579 places at the same time. 02:24.580 --> 02:29.360 So the only alternative seems to be to say that neither of us 02:29.356 --> 02:32.666 is Shelly Kagan. But if neither of us is Shelly 02:32.671 --> 02:36.561 Kagan, then the simple original personality theory was false. 02:36.560 --> 02:39.680 Because according to that theory, having the personality 02:39.680 --> 02:41.780 is what it took to be Shelly Kagan. 02:41.780 --> 02:44.060 We both have it, yet neither of us is Shelly 02:44.056 --> 02:45.836 Kagan. The personality theory must be 02:45.842 --> 02:48.512 false. So we revise the personality 02:48.505 --> 02:52.275 theory to say, the secret to personal identity 02:52.275 --> 02:55.955 is having the same personality--provided that 02:55.961 --> 02:58.141 there's no branching. 02:58.140 --> 03:00.190 Provided there's no splitting. 03:00.189 --> 03:05.439 Provided there's only one best competitor, not two equally good 03:05.439 --> 03:08.669 candidates. Given the no branching view, 03:08.668 --> 03:12.388 the no branching rule, we can say, in the ordinary 03:12.391 --> 03:14.441 case, look, there really wasn't 03:14.444 --> 03:17.224 anybody imprinted with my memories and desires in 03:17.216 --> 03:19.656 Michigan. I'm the only one around in the 03:19.655 --> 03:23.025 earth right now with Shelly Kagan's memories and desires. 03:23.030 --> 03:26.790 Since there's no competitor, and I've got the personality, 03:26.794 --> 03:28.054 I'm Shelly Kagan. 03:28.050 --> 03:31.380 I'm the very same person that was here lecturing to you last 03:31.384 --> 03:33.214 week. That's what the personality 03:33.207 --> 03:36.057 theory--It gives us the answer we're looking for in the 03:36.061 --> 03:38.711 ordinary case. But in the science fiction 03:38.713 --> 03:41.683 story where there's a duplicate, it says, uh, 03:41.682 --> 03:45.462 if there's branching, the no branching rule comes in. 03:45.460 --> 03:48.570 Neither of them is Shelly Kagan. 03:48.569 --> 03:51.759 All right, so that's the best way for the personality theory 03:51.762 --> 03:54.092 to get revised to deal with this problem. 03:54.090 --> 03:56.820 The trouble was, it seems the no branching rule 03:56.820 --> 03:58.660 seems very counter-intuitive. 03:58.660 --> 03:59.280 So think about it. 03:59.280 --> 04:03.020 Here, right now I'm standing in front of you saying I'm Shelly 04:03.015 --> 04:06.195 Kagan, the guy who was lecturing to you last week. 04:06.199 --> 04:09.279 I believe I'm Shelly Kagan, the guy who was lecturing to 04:09.275 --> 04:11.655 you last week. Am I Shelly Kagan? 04:11.659 --> 04:13.789 Well, I've got Shelly Kagan's personality. 04:13.790 --> 04:16.710 So far so good. Now all we have to decide is, 04:16.712 --> 04:19.542 was the branching rule satisfied or violated? 04:19.540 --> 04:22.420 So all we have to know is, is there somebody else 04:22.420 --> 04:26.140 somewhere in the universe who's got all my memories and beliefs 04:26.139 --> 04:29.739 and desires? Well, how in the world could I 04:29.741 --> 04:32.961 know that? Whether I, this person talking 04:32.963 --> 04:36.193 to you right now, is Shelly Kagan depends on 04:36.192 --> 04:40.852 whether there's some duplicate with all my memories in Michigan 04:40.848 --> 04:44.688 or not? It seems very counter-intuitive. 04:44.690 --> 04:50.470 So although the personality with no branching rule avoids 04:50.471 --> 04:55.221 the problem of what to say about duplicates, 04:55.220 --> 04:58.570 by saying when there's branching, neither of them is 04:58.572 --> 05:01.472 Shelly Kagan, the branching rule itself seems 05:01.465 --> 05:03.235 very counter-intuitive. 05:03.240 --> 05:06.490 We feel as though whether somebody is me or not should 05:06.487 --> 05:10.407 depend upon internal facts about me in the earlier stages or this 05:10.408 --> 05:14.998 stage and that stage, not about what's happening 05:15.003 --> 05:20.543 elsewhere, outside, extrinsic to these things. 05:20.540 --> 05:23.430 So, if you're not willing to accept the no branching rule, 05:23.434 --> 05:26.434 if it strikes you as a bizarre thing to throw in to personal 05:26.429 --> 05:28.919 identity, maybe you need to reject the 05:28.921 --> 05:30.231 personality theory. 05:30.230 --> 05:34.600 Now during all of this, the fans of the body view 05:34.602 --> 05:36.882 typically are laughing. 05:36.879 --> 05:42.279 They say this just goes to show what a dumb theory the 05:42.283 --> 05:44.733 personality theory is. 05:44.730 --> 05:47.880 The whole problem with the personality theory is that 05:47.884 --> 05:50.254 personality is a bit like a software. 05:50.250 --> 05:51.600 It's like programs. 05:51.600 --> 05:55.120 It's the various programs you run on your computer along with 05:55.117 --> 05:58.687 the various data files that you have saved on your hard drive, 05:58.693 --> 06:02.023 and so forth. And those can be duplicated. 06:02.019 --> 06:03.619 You have copy after copy after copy. 06:03.620 --> 06:06.540 You can have two copies of my personality. 06:06.540 --> 06:09.400 You could have 100 or 1,000. 06:09.399 --> 06:13.929 The problem with--what drove the personality theory into the 06:13.925 --> 06:17.235 no branching rule, implausible as it may be, 06:17.238 --> 06:21.008 was the fact that your personality is like software, 06:21.010 --> 06:23.520 and it can be copied. 06:23.519 --> 06:27.649 That's why, they say, we should believe in the body 06:27.651 --> 06:30.731 view. If we accept the body view, 06:30.726 --> 06:33.866 we avoid the duplication problem. 06:33.870 --> 06:38.930 Because, unlike software, which can be literally copied, 06:38.931 --> 06:43.901 as many as you want identical, the body can't split. 06:43.899 --> 06:48.729 Human bodies can't divide or branch. 06:48.730 --> 06:51.940 There's no way that there's another body, 06:51.943 --> 06:55.643 that the body on Thursday became two bodies. 06:55.639 --> 06:57.879 The body that was here on Thursday didn't, 06:57.883 --> 06:59.473 couldn't become two bodies. 06:59.470 --> 07:01.000 So we avoid all the problem. 07:01.000 --> 07:05.890 That's at least the kind of claim that fans of the body view 07:05.892 --> 07:10.872 often make in the face of this difficulty for the personality 07:10.867 --> 07:12.997 theory. Well, now we need to ask, 07:13.001 --> 07:13.931 is it really true? 07:13.930 --> 07:19.200 Is it really true that bodies don't face a duplication 07:19.196 --> 07:22.506 problem? Is it really true that human 07:22.512 --> 07:25.252 bodies don't and couldn't split? 07:25.250 --> 07:28.380 Look, the crucial word here is, of course, "couldn't." 07:28.379 --> 07:31.119 Personalities don't actually split either, 07:31.116 --> 07:32.886 right? Although I've been giving 07:32.886 --> 07:35.356 science fiction examples in which the mad scientist 07:35.358 --> 07:37.828 duplicates my memories and beliefs and desires, 07:37.829 --> 07:40.539 they've all been science fiction examples. 07:40.540 --> 07:44.330 If I can use science fiction to talk about the possibility of 07:44.329 --> 07:47.929 splitting, and use that against the personality theory, 07:47.930 --> 07:51.840 I'm entitled to use science fiction examples to talk about 07:51.841 --> 07:54.451 the possibility of bodies splitting, 07:54.449 --> 07:58.829 and ask, what kind of problem that would raise for the body 07:58.830 --> 08:02.910 theory? Now, we are familiar with some 08:02.912 --> 08:07.452 low-level examples of bodies splitting. 08:07.450 --> 08:10.550 Amoebas split, right? 08:10.550 --> 08:11.800 You've got a single amoeba. 08:11.800 --> 08:12.740 It's going along. 08:12.740 --> 08:17.100 At a certain point--Let's draw our amoeba splitting, 08:17.096 --> 08:20.336 right? You've got an amoeba split, 08:20.338 --> 08:24.008 going along. At a certain point, 08:24.008 --> 08:27.728 it starts to look like that. 08:27.730 --> 08:30.440 Then it looks like that. 08:30.440 --> 08:33.920 And then boom! You've got, well, it splits. 08:33.920 --> 08:37.130 08:37.129 --> 08:42.239 There's nothing in biology per se that rules out cell division. 08:42.240 --> 08:43.430 Indeed, on the contrary, right? 08:43.430 --> 08:46.080 We know cells can split. 08:46.080 --> 08:48.500 Now, human bodies, unlike amoebas, 08:48.504 --> 08:51.294 don't do that. But maybe there's nothing in 08:51.289 --> 08:53.589 biology that rules out the possibility. 08:53.590 --> 08:57.740 Suppose we open up the Yale Daily tomorrow and we see 08:57.736 --> 09:02.086 that the Yale Center for Amoebic Studies has made this tremendous 09:02.087 --> 09:05.007 breakthrough and has discovered how to, 09:05.009 --> 09:09.199 through the right kind of injection or whatever, 09:09.195 --> 09:14.355 cause a human body to replicate and split in an amoeba-like 09:14.361 --> 09:17.641 fashion. Well, then we have to face the 09:17.640 --> 09:21.840 problem of what to say in this case of bodily branching. 09:21.840 --> 09:24.610 Well, instead of pursuing that example, let me give you a 09:24.610 --> 09:27.480 slightly different example that's been discussed a fair bit 09:27.479 --> 09:29.259 in the philosophical literature. 09:29.260 --> 09:34.180 09:34.179 --> 09:37.269 This is actually a case that one of the students in the class 09:37.269 --> 09:40.719 asked about, I think it was last week, if it wasn't even earlier. 09:40.720 --> 09:41.930 And I said, "Great question. 09:41.930 --> 09:43.260 Let's come back to it." 09:43.259 --> 09:46.309 So here, at long last, I'm making good on my 09:46.312 --> 09:49.692 promissory note. I'm going to come back to the 09:49.686 --> 09:51.996 example that was raised before. 09:52.000 --> 09:55.040 You'll recall that when we talked about the body view, 09:55.035 --> 09:58.405 I said the best version of the body view doesn't require the 09:58.413 --> 10:01.353 entire body, to be the same body, 10:01.347 --> 10:04.397 but the brain. Follow the brain. 10:04.399 --> 10:07.499 And indeed, it doesn't seem as though we have to require the 10:07.497 --> 10:09.647 entire brain, just enough of the brain, 10:09.649 --> 10:12.729 however much that turns out, to house personality, 10:12.730 --> 10:14.240 memories and so forth. 10:14.240 --> 10:17.750 10:17.750 --> 10:20.560 And then, I said, suppose it was possible that 10:20.559 --> 10:23.119 one hemisphere of your brain is enough. 10:23.120 --> 10:27.750 If there's enough redundancy in the brain so that even if your 10:27.746 --> 10:31.106 right hemisphere got destroyed, your left hemisphere, 10:31.109 --> 10:32.949 you still have all the same memories, desires, 10:32.950 --> 10:36.030 beliefs. Good enough. 10:36.029 --> 10:38.169 So now we worry about the following case. 10:38.169 --> 10:40.679 So I gave you a bunch of examples, right, 10:40.683 --> 10:44.143 where there are brains being transplanted into torsos of 10:44.138 --> 10:47.478 others. So suppose, gruesome as it was, 10:47.482 --> 10:52.102 this weekend I'm in some horrible accident and my torso 10:52.102 --> 10:56.982 gets destroyed and they keep my brain on life support, 10:56.980 --> 11:02.920 oxygenating it just long enough to do some radical surgery into 11:02.915 --> 11:04.825 some spare torsos. 11:04.830 --> 11:06.090 Where'd the torsos come from? 11:06.090 --> 11:09.390 Well, you had some living people, but they had very rare 11:09.389 --> 11:12.509 brain diseases and their brain suddenly liquefied. 11:12.509 --> 11:13.579 So now we've got some spare torsos. 11:13.580 --> 11:16.900 11:16.899 --> 11:26.879 All right, so here we've got Shelly Kagan. 11:26.880 --> 11:27.710 His body gets destroyed. 11:27.710 --> 11:31.590 11:31.590 --> 11:32.300 And here's my brain. 11:32.300 --> 11:36.910 11:36.909 --> 11:42.119 Over here we've got Jones' torso. 11:42.120 --> 11:47.260 11:47.259 --> 11:48.949 And over here we've got Smith's torso. 11:48.950 --> 11:57.700 11:57.700 --> 12:04.690 Suppose we take, call this one the left 12:04.687 --> 12:15.167 hemisphere, and we stick it in here, into Jones' torso. 12:15.169 --> 12:19.539 We take this other hemisphere, the right half of my brain and 12:19.544 --> 12:21.954 we stick it into Smith's torso. 12:21.950 --> 12:26.090 12:26.090 --> 12:28.650 We connect all the wires, all the neurons. 12:28.649 --> 12:31.309 The operation's a smashing success. 12:31.310 --> 12:32.410 Both things wake up. 12:32.410 --> 12:36.910 12:36.909 --> 12:43.679 So here's Jones' torso with the left half of SK's brain. 12:43.679 --> 12:46.529 Smith's torso with the right half of SK's brain. 12:46.530 --> 12:51.370 12:51.370 --> 12:53.370 They wake up. We need some way to refer to 12:53.369 --> 12:55.079 these people, so we can start talking about 12:55.078 --> 12:57.468 who they are. Let me just call this top 12:57.470 --> 13:01.160 one--Jones' torso with the left half of Shelly Kagan's 13:01.161 --> 13:03.321 brain--let's call him Lefty. 13:03.320 --> 13:06.470 13:06.470 --> 13:08.980 Smith's torso with the right half of Shelly Kagan's brain, 13:08.982 --> 13:10.042 let's call him Righty. 13:10.040 --> 13:13.830 13:13.830 --> 13:18.470 Okay, operation's a success. 13:18.470 --> 13:21.500 Lefty and Righty both wake up. 13:21.500 --> 13:26.310 They both think they're Shelly Kagan, and so forth and so on. 13:26.309 --> 13:31.469 And we ask ourselves, according to the body view, 13:31.470 --> 13:34.480 which one is Shelly Kagan? 13:34.480 --> 13:36.090 What are the possibilities? 13:36.090 --> 13:41.800 We could say Lefty is Shelly Kagan and Righty is not. 13:41.800 --> 13:44.380 Righty's an imposter. 13:44.379 --> 13:49.109 But there's nothing in the body view to give us a reason to make 13:49.109 --> 13:52.169 that choice. It's true that Lefty's got half 13:52.173 --> 13:55.293 of Shelly Kagan's brain and that's good enough. 13:55.289 --> 13:59.089 But it's also true that Righty's got half of Shelly 13:59.085 --> 14:02.345 Kagan's brain and that seems good enough. 14:02.350 --> 14:05.720 So there's no reason to say that Lefty is Shelly Kagan and 14:05.722 --> 14:07.302 Righty isn't. And similarly, 14:07.298 --> 14:10.098 of course, there's nothing in the body view to make us say 14:10.099 --> 14:12.409 that Righty is Shelly Kagan and Lefty isn't. 14:12.410 --> 14:16.010 14:16.009 --> 14:17.559 Well, if it's not one, and not the other, 14:17.564 --> 14:19.084 what are the remaining possibilities? 14:19.080 --> 14:23.930 We could, I suppose, try to say they're both 14:23.926 --> 14:26.996 Shelly Kagan. And so Shelly Kagan continues, 14:27.001 --> 14:29.811 that is to say his body continues, that is to say his 14:29.812 --> 14:32.732 brain continues, that is to say enough of his 14:32.726 --> 14:35.076 brain continues, merrily on its way, 14:35.083 --> 14:36.973 except now in two places. 14:36.970 --> 14:40.440 And so from now on, Shelly Kagan, 14:40.437 --> 14:45.637 that single person, is in two different places at 14:45.639 --> 14:50.509 the same time. Lefty goes to California. 14:50.510 --> 14:53.520 Righty moves to Vermont. 14:53.519 --> 14:55.589 From now on, Shelly Kagan's bicoastal. 14:55.590 --> 14:58.760 14:58.760 --> 15:01.020 It doesn't seem right. 15:01.019 --> 15:02.839 So what else can the body theory say? 15:02.840 --> 15:05.970 Well, the body theory could say neither of them are 15:05.967 --> 15:09.527 Shelly Kagan. Shelly Kagan died in that 15:09.526 --> 15:12.696 gruesome, horrible accident. 15:12.700 --> 15:15.520 Although it's true that we now have two people, 15:15.521 --> 15:18.471 Lefty and Righty, each of whom has half of Shelly 15:18.465 --> 15:20.825 Kagan's brain, and all of Shelly Kagan's 15:20.825 --> 15:23.885 memories, for whatever that's worth, neither of them is Shelly 15:23.888 --> 15:26.998 Kagan. We could say that as well. 15:27.000 --> 15:29.840 But if we--and that seems the least unpalatable of the 15:29.844 --> 15:32.214 alternatives. But if we say that, 15:32.206 --> 15:35.316 then we've given up on the body view. 15:35.320 --> 15:39.100 Because the body view, after all, said to be Shelly 15:39.100 --> 15:42.880 Kagan is to have enough of Shelly Kagan's brain. 15:42.879 --> 15:45.599 And in this case, both of Lefty and Righty seem 15:45.602 --> 15:48.032 to have enough of Shelly Kagan's brain. 15:48.030 --> 15:51.280 15:51.280 --> 15:54.270 What's the body theorist to do? 15:54.269 --> 15:58.189 As far as I can see, the best option for the body 15:58.188 --> 16:02.758 theorist at this point is to add--no surprises here--a no 16:02.759 --> 16:06.499 branching rule. The body theorist should say, 16:06.498 --> 16:10.648 "The key to personal identity is having the same body, 16:10.649 --> 16:14.179 to wit, the same brain, to wit, enough of the brain to 16:14.180 --> 16:17.580 keep the personality going--provided that there's no 16:17.577 --> 16:20.117 branching, no splitting, 16:20.116 --> 16:24.436 no perfect competitors, only one." 16:24.440 --> 16:28.340 If the body view adds the no branching principle, 16:28.338 --> 16:32.078 then we can say, look, in the case of this sort 16:32.075 --> 16:36.705 of splitting--This example is known in theto philosophical 16:36.705 --> 16:40.765 literature as fission, like nuclear fission when a big 16:40.769 --> 16:42.039 atom splits into two. 16:42.039 --> 16:44.759 So, in the fission case, the body says, 16:44.762 --> 16:47.842 the body theorist says, in the fission case, 16:47.842 --> 16:50.782 there's splitting, there's branching. 16:50.779 --> 16:54.749 So neither of them is going to end up being Shelly Kagan. 16:54.750 --> 16:58.910 But in the ordinary humdrum case, here I am, 16:58.912 --> 17:01.202 my body. Why am I Shelly Kagan? 17:01.200 --> 17:04.360 Because the brain in front of you--you can't see it, 17:04.360 --> 17:07.890 but it's in front of you--the brain in front of you is the 17:07.893 --> 17:11.553 very same brain as the brain that you had in front of you on 17:11.550 --> 17:13.230 Thursday. Follow the body, 17:13.233 --> 17:14.743 in particular follow the brain. 17:14.740 --> 17:18.480 So in the ordinary case, no splitting, 17:18.479 --> 17:20.399 follow the brain. 17:20.400 --> 17:23.930 In the special case where there's splitting, 17:23.929 --> 17:27.869 even if you follow the brain, not good enough. 17:27.869 --> 17:33.559 So the body theorist can avoid the problem of fission, 17:33.558 --> 17:38.708 avoid the problem of duplication by adding the no 17:38.710 --> 17:42.260 branching rule. But of course, 17:42.261 --> 17:47.661 the no branching rule didn't seem very intuitive. 17:47.660 --> 17:50.130 Whether or not I'm Shelly Kagan, the guy that was 17:50.126 --> 17:52.826 lecturing to you on Thursday, depends on whether, 17:52.826 --> 17:54.866 unbeknownst to me, over the weekend, 17:54.865 --> 17:57.015 somebody removed half of my brain, 17:57.019 --> 17:59.629 stuck it in some other torso, sealed me all back up. 17:59.630 --> 18:03.340 18:03.340 --> 18:04.830 How could that matter? 18:04.830 --> 18:09.150 18:09.150 --> 18:13.460 Well, if you don't find the no branching rule plausible, 18:13.456 --> 18:16.506 you're in trouble as a body theorist. 18:16.509 --> 18:20.979 In fact, so what we see is, the body theory is in exactly 18:20.981 --> 18:24.491 the same problem, exactly the same situation, 18:24.494 --> 18:26.894 as the personality theory. 18:26.890 --> 18:31.830 Indeed, the fission example is a very nice case of how you 18:31.833 --> 18:36.173 could have splitting for the personality theory. 18:36.170 --> 18:38.690 Here, before the accident, was Shelly Kagan, 18:38.685 --> 18:41.375 somebody who had my beliefs, desires, memories, 18:41.376 --> 18:42.776 goals, and so forth. 18:42.779 --> 18:46.009 After the accident, we've got two people, 18:46.006 --> 18:48.906 Lefty and Righty, or two entities, 18:48.910 --> 18:52.280 Lefty and Righty, both of whom have Shelly 18:52.284 --> 18:55.334 Kagan's memories, beliefs, desires, 18:55.330 --> 18:58.070 goals, and so forth. 18:58.069 --> 19:01.659 Splitting the brain shows how you could, in fact, 19:01.663 --> 19:04.063 have splitting of personality. 19:04.059 --> 19:09.179 So the very same case raises the very same problem for both 19:09.180 --> 19:12.800 the body view and the personality view. 19:12.799 --> 19:16.099 And the only solution that I can see, at least the best 19:16.100 --> 19:19.340 solution that I can see, is to accept the no branching 19:19.339 --> 19:21.669 rule. If you don't like the no 19:21.671 --> 19:24.571 branching rule, it's not clear what your 19:24.565 --> 19:26.045 alternatives are. 19:26.049 --> 19:27.479 Or at least, it is clear what your 19:27.484 --> 19:29.724 alternatives are; it's not clear which 19:29.717 --> 19:32.037 alternative would be any better. 19:32.039 --> 19:35.849 Now during all of this--problems for the 19:35.848 --> 19:39.748 personality theory, problems for the body 19:39.754 --> 19:45.034 view--during all of this, the soul theorist is having a 19:45.027 --> 19:48.897 field day. The soul theorist is saying, 19:48.899 --> 19:52.529 "Look you guys, you got into all this trouble 19:52.528 --> 19:55.908 with splitting and so forth and so on, 19:55.910 --> 19:58.760 and needing to add the no branching rule, 19:58.756 --> 20:01.456 silly and implausible as that seems, 20:01.460 --> 20:03.920 you got into all that trouble because of the problem of 20:03.924 --> 20:06.074 splitting because personalities can be split, 20:06.070 --> 20:07.050 bodies can be split. 20:07.049 --> 20:12.079 If only you had seen the light and stuck to the soul theory of 20:12.083 --> 20:15.803 personal identity, all these problems could be 20:15.797 --> 20:18.397 avoided." Now, as you know, 20:18.396 --> 20:20.726 I don't believe in souls. 20:20.730 --> 20:22.690 But forget that issue for the moment. 20:22.690 --> 20:26.110 Let's just ask the question, "Is it true that the soul 20:26.110 --> 20:29.790 theory--if only there were souls--is it true that the soul 20:29.789 --> 20:33.339 theory would at least have the following advantage? 20:33.339 --> 20:38.799 It avoids these problems of duplication and fission." 20:38.800 --> 20:44.290 Well let's ask. What should a soul theorist say 20:44.289 --> 20:47.099 about the fission case? 20:47.100 --> 20:50.330 So here's the gruesome accident. 20:50.330 --> 20:54.180 My brain gets split apart. 20:54.180 --> 20:57.180 One part gets put into Jones' torso. 20:57.180 --> 21:00.640 One part gets put into Smith's torso. 21:00.640 --> 21:04.050 After the operation, Lefty wakes up thinking he's 21:04.053 --> 21:06.803 Shelly Kagan. Smith wakes up thinking he's 21:06.799 --> 21:09.119 Shelly Kagan. Lefty's got part of Shelly 21:09.123 --> 21:12.093 Kagan's brain. Smith's, or rather Righty's got 21:12.089 --> 21:14.129 part of Shelly Kagan's brain. 21:14.130 --> 21:20.590 What should the soul theorist say about the case of fission? 21:20.589 --> 21:23.769 Well, again, remember, the soul theory says 21:23.766 --> 21:27.846 the key to being the same person is having the soul. 21:27.849 --> 21:31.159 Why am I the person that was lecturing to you on Thursday? 21:31.160 --> 21:35.140 Because it's the very same soul animating my body, 21:35.144 --> 21:36.694 or what have you. 21:36.690 --> 21:44.870 So, what does the soul theorist say about the fission case? 21:44.869 --> 21:49.099 I'm not quite sure, because we have to turn to a 21:49.096 --> 21:53.766 metaphysical question that we've touched upon before, 21:53.772 --> 21:56.292 namely, can souls split? 21:56.289 --> 21:59.509 After all, the problem that fission raises for the 21:59.513 --> 22:01.683 personality theory, in a nutshell, 22:01.683 --> 22:05.173 is that personalities can split, they can branch. 22:05.170 --> 22:07.550 The problem for the body view that fission raises, 22:07.549 --> 22:09.589 in a nutshell, is that bodies can split. 22:09.590 --> 22:14.270 They can branch. We need to ask about the 22:14.270 --> 22:19.120 metaphysics of the soul, can souls split? 22:19.119 --> 22:21.429 And I don't know the answer to that, of course. 22:21.430 --> 22:23.950 So let's consider both possibilities. 22:23.950 --> 22:25.410 Possibility number one. 22:25.410 --> 22:27.960 Souls, just like bodies, just like personalities, 22:27.961 --> 22:28.601 can split. 22:28.600 --> 22:32.130 22:32.130 --> 22:33.530 Suppose that's what happened. 22:33.529 --> 22:36.989 So, there was a single soul here, Shelly Kagan's soul, 22:36.985 --> 22:40.045 but in the middle of this gruesome operation, 22:40.049 --> 22:44.399 gruesome accident and followed by this amazing operation, 22:44.396 --> 22:46.566 Shelly Kagan's soul split. 22:46.569 --> 22:53.949 So there's one of the SK souls over here and there's one of the 22:53.953 --> 22:58.363 SK souls in the other case as well. 22:58.359 --> 23:05.179 Each one of Lefty and Righty has one of the pieces of the 23:05.175 --> 23:08.335 split Shelly Kagan soul. 23:08.339 --> 23:12.269 All right, so now we ask ourselves, "According to the 23:12.267 --> 23:15.437 soul theory, which one is Shelly Kagan?" 23:15.440 --> 23:18.150 Well, you--By this point, you can run through all the 23:18.151 --> 23:19.821 possibilities yourself, right? 23:19.819 --> 23:23.749 We could say, well, it's Lefty and not 23:23.753 --> 23:26.353 Righty. But there's nothing in the soul 23:26.347 --> 23:28.087 theory that supports that claim. 23:28.089 --> 23:31.499 They each have an equally good--however good it may 23:31.501 --> 23:35.531 be--they've got an equally good piece of the original Shelly 23:35.526 --> 23:38.156 Kagan soul. So there's no reason to say 23:38.158 --> 23:40.838 that Lefty is Shelly Kagan and Righty isn't. 23:40.839 --> 23:44.769 There's no good reason to say Righty is Shelly Kagan and Lefty 23:44.774 --> 23:46.884 isn't. Well, would it be better to say 23:46.876 --> 23:49.736 they're both Shelly Kagan, as long as you've got a 23:49.742 --> 23:53.022 piece of Shelly Kagan's soul, of the original soul, 23:53.016 --> 23:55.506 then you just are Shelly Kagan? 23:55.509 --> 23:59.099 In which case, Lefty and Righty are both 23:59.097 --> 24:02.407 Shelly Kagan, and Shelly Kagan is now 24:02.408 --> 24:06.458 bicoastal, one in California, one in Vermont, 24:06.456 --> 24:10.496 one part of him? That doesn't seem very 24:10.498 --> 24:12.598 satisfying. What's the alternative? 24:12.599 --> 24:14.759 The alternative, it seems, for the soul 24:14.762 --> 24:17.322 theorist, is to say, neither of them is 24:17.322 --> 24:18.292 Shelly Kagan. 24:18.290 --> 24:22.150 24:22.150 --> 24:25.190 Neither of them is Shelly Kagan, then Shelly Kagan died. 24:25.190 --> 24:28.410 But how can we say that if we accept the soul theory? 24:28.410 --> 24:30.660 They both have pieces of Shelly Kagan's soul. 24:30.660 --> 24:36.510 The soul split. Well, maybe what the soul 24:36.507 --> 24:40.647 theorist would have to do at this point is accept 24:40.648 --> 24:44.098 the--da-ta-da--the no branching rule. 24:44.099 --> 24:47.769 "Ah," says the soul theorist, "Follow the soul--unless the 24:47.769 --> 24:51.049 soul splits, in which case neither of them is Shelly 24:51.051 --> 24:51.761 Kagan." 24:51.760 --> 24:56.450 24:56.450 --> 25:00.430 Well, the trouble is, we didn't find the no branching 25:00.427 --> 25:02.107 rule very plausible. 25:02.110 --> 25:04.820 It seemed counterintuitive. 25:04.819 --> 25:07.719 But at this point, you begin to wonder, 25:07.719 --> 25:11.229 maybe we just need to learn to live with it. 25:11.230 --> 25:14.700 If the personality theory needs the no branching rule, 25:14.703 --> 25:17.983 and the body theory needs the no branching rule, 25:17.980 --> 25:21.820 and the soul theory needs the no branching rule, 25:21.820 --> 25:26.070 maybe we're just stuck with the no branching rule, 25:26.070 --> 25:28.780 whether or not we like it. 25:28.779 --> 25:31.889 And if we're stuck with it, then of course it's not an 25:31.887 --> 25:35.227 objection against any one of the theories that uses it. 25:35.230 --> 25:38.800 Well, this is all what we would say as soul theorists if we 25:38.801 --> 25:40.281 think souls can split. 25:40.279 --> 25:44.689 But we need to consider the possibility that souls can't 25:44.688 --> 25:47.838 split. Maybe the soul theorist has an 25:47.835 --> 25:52.675 alternative available to it that--available to him that the 25:52.678 --> 25:55.098 other theories don't have. 25:55.099 --> 26:01.929 Suppose Shelly Kagan's soul cannot split. 26:01.930 --> 26:03.420 What does that mean? 26:03.420 --> 26:10.280 It means, when my brain gets split, my soul is going to end 26:10.277 --> 26:15.477 up in Lefty or in Righty, but not in both. 26:15.480 --> 26:18.960 If a soul can't split, you can't end up with pieces of 26:18.956 --> 26:22.036 the soul or the remnants of the soul in both. 26:22.039 --> 26:23.919 The soul is a unified simple thing. 26:23.920 --> 26:28.890 Now, I don't actually know whether it's true that simple 26:28.891 --> 26:30.791 things can't split. 26:30.789 --> 26:32.349 Metaphysically, I'm not sure whether that's a 26:32.346 --> 26:33.086 possibility or not. 26:33.089 --> 26:37.429 But let's just suppose--look, Plato argued the soul was 26:37.427 --> 26:39.797 simple. He didn't actually convince me 26:39.797 --> 26:42.427 of that, but suppose we thought souls are simple, 26:42.433 --> 26:44.743 and we think simple things can't split. 26:44.740 --> 26:47.090 It would follow, then, that souls can't split. 26:47.089 --> 26:49.599 Suppose we accept all that metaphysics. 26:49.599 --> 26:53.059 Then the question is just, which one is Shelly Kagan? 26:53.059 --> 26:58.769 Well, it depends which one ended up with Shelly Kagan's 26:58.769 --> 27:00.459 soul. We can't say, 27:00.458 --> 27:02.208 they both have a piece. 27:02.210 --> 27:06.890 One of them will have it, the other one won't. 27:06.890 --> 27:09.170 And you want to know which one's Shelly Kagan? 27:09.170 --> 27:14.440 The one that actually ends up with Shelly Kagan's soul. 27:14.440 --> 27:17.840 If Lefty ends up with Shelly Kagan's soul, 27:17.839 --> 27:22.399 then Lefty is Shelly Kagan and Righty is an imposter. 27:22.400 --> 27:24.610 He thinks he's Shelly Kagan, but he's not, 27:24.610 --> 27:27.090 because he doesn't have Shelly Kagan's soul. 27:27.090 --> 27:32.550 Lefty has it. If Righty's got Shelly Kagan's 27:32.550 --> 27:38.550 soul, then Righty is Shelly Kagan and Lefty is the imposter. 27:38.549 --> 27:43.669 Now, looking at the situation from the outside, 27:43.669 --> 27:49.459 we might be unable to tell which one is really Shelly 27:49.457 --> 27:52.527 Kagan. Because we won't be able to 27:52.530 --> 27:56.670 tell, looking at it from the outside, which one really has 27:56.669 --> 27:58.339 Shelly Kagan's soul. 27:58.339 --> 28:01.379 Although it will be true, whichever one really does have 28:01.379 --> 28:03.479 Shelly Kagan's soul is Shelly Kagan. 28:03.480 --> 28:06.510 But we don't know which one that is. 28:06.509 --> 28:10.199 Interestingly, and somewhat more surprisingly, 28:10.195 --> 28:14.615 looking at it from the inside, we won't be able to tell 28:14.618 --> 28:16.978 either. Lefty will say, 28:16.983 --> 28:18.743 "Give me a break. 28:18.740 --> 28:20.470 Of course I'm Shelly Kagan. 28:20.470 --> 28:23.290 Of course I've got Shelly Kagan's soul. 28:23.290 --> 28:26.610 Of course I'm the one." 28:26.609 --> 28:29.769 But Righty will also say, "Give me a break. 28:29.770 --> 28:31.400 Of course I'm Shelly Kagan. 28:31.400 --> 28:33.600 Of course I've got Shelly Kagan's soul. 28:33.600 --> 28:35.930 Of course I'm the one." 28:35.930 --> 28:41.310 If souls can't split, one of them is mistaken. 28:41.309 --> 28:43.939 But there's no way for them to know which one is the one that's 28:43.942 --> 28:44.412 deceived. 28:44.410 --> 28:48.760 28:48.759 --> 28:52.349 Now, that may not be a problem that you're unwilling to 28:52.345 --> 28:54.405 swallow. As we've seen, 28:54.407 --> 28:58.797 all the views here have their difficulties. 28:58.799 --> 29:03.089 Maybe that's the difficulty you're prepared to accept. 29:03.089 --> 29:05.009 What's the right answer in fission? 29:05.009 --> 29:08.399 It depends on who's got Shelly Kagan's soul. 29:08.400 --> 29:11.390 No way to tell. But still, that's the answer to 29:11.391 --> 29:12.761 the metaphysical question. 29:12.760 --> 29:14.910 Question? Student: What happens if 29:14.908 --> 29:16.558 neither of these had Shelly Kagan's soul? 29:16.559 --> 29:19.449 Professor Shelly Kagan: The question was, 29:19.445 --> 29:22.755 "What if neither of these have Shelly Kagan's soul?" 29:22.760 --> 29:25.290 Then they're both imposters. 29:25.289 --> 29:28.829 That's a little bit like the case we worried about when we 29:28.826 --> 29:31.676 started thinking about the soul view, right? 29:31.680 --> 29:38.150 What if last night God destroyed my soul and put in a 29:38.151 --> 29:41.511 new soul? Then Shelly Kagan died. 29:41.509 --> 29:46.919 If Shelly Kagan's soul does not migrate to Lefty or Righty, 29:46.920 --> 29:51.860 neither of them is Shelly Kagan, according to the soul 29:51.863 --> 29:54.343 theory. What happened to Shelly Kagan? 29:54.339 --> 29:57.489 Well, if the soul got destroyed, Shelly Kagan died. 29:57.490 --> 30:00.100 If the soul didn't get destroyed, maybe somebody else 30:00.100 --> 30:02.610 that we weren't even looking at is Shelly Kagan. 30:02.610 --> 30:08.770 30:08.769 --> 30:11.859 So as I say, the soul theory can at least 30:11.855 --> 30:16.015 give us an answer that avoids the no branching rule. 30:16.019 --> 30:20.479 If souls are simples and simples can't split, 30:20.483 --> 30:25.453 there's no possibility of having two things with a 30:25.454 --> 30:29.464 relevant soul. So we don't need to add, 30:29.464 --> 30:34.384 in this ad hoc fashion, the no branching rule. 30:34.380 --> 30:37.170 That's an advantage for the soul theory, if only we believed 30:37.169 --> 30:39.749 in souls. It is an advantage. 30:39.750 --> 30:44.670 But I need to point out that there's another disadvantage 30:44.674 --> 30:49.164 that the fission case raises for the soul theory. 30:49.160 --> 30:55.420 So let's just suppose that metaphysically God tells us that 30:55.423 --> 30:59.963 it's Lefty that has Shelly Kagan's soul. 30:59.960 --> 31:02.640 Then of course it's Lefty that is Shelly Kagan. 31:02.640 --> 31:05.340 Righty is an imposter. 31:05.339 --> 31:09.479 Righty believes he's Shelly Kagan, he has all the memories 31:09.483 --> 31:12.463 of Shelly Kagan, all the desires of Shelly 31:12.463 --> 31:14.303 Kagan, but he's not Shelly Kagan 31:14.300 --> 31:16.300 because he doesn't have Shelly Kagan's soul. 31:16.300 --> 31:20.640 Lefty happens to have it. 31:20.640 --> 31:24.150 That's a nice answer to the problem of fission, 31:24.147 --> 31:28.107 but notice the problem it raises for the argument for 31:28.111 --> 31:31.391 believing in a soul in the first place. 31:31.390 --> 31:34.130 Way back at the start of the semester when we asked, 31:34.134 --> 31:35.484 "Why believe in souls?" 31:35.480 --> 31:40.640 one important argument was, or really family of arguments 31:40.635 --> 31:45.785 was, you need to believe in souls in order to explain why 31:45.790 --> 31:49.450 bodies are animated, why people are rational, 31:49.448 --> 31:51.318 how they can have personalities, 31:51.319 --> 31:55.479 how they can be creative, and so forth. 31:55.480 --> 31:57.220 In order to explain consciousness and 31:57.218 --> 31:59.388 self-awareness. Whatever it was, 31:59.387 --> 32:03.847 fill in your favorite blank, fill in the blank in your 32:03.852 --> 32:06.352 favorite way. The claim was, 32:06.346 --> 32:11.336 you needed to believe in souls in order to explain all that. 32:11.339 --> 32:14.599 But if that's right, what's going on in Righty's 32:14.603 --> 32:17.093 case? Righty is aware. 32:17.090 --> 32:19.160 Righty is conscious. 32:19.160 --> 32:20.830 Righty is creative. 32:20.830 --> 32:22.400 Righty has free will. 32:22.400 --> 32:23.840 Righty makes plans. 32:23.840 --> 32:25.340 Righty's got personality. 32:25.340 --> 32:26.560 Righty is rational. 32:26.560 --> 32:30.020 Righty's body is animated. 32:30.019 --> 32:32.989 According to the soul-theory argument for soul, 32:32.994 --> 32:35.974 rather, according to the argument for souls, 32:35.970 --> 32:41.340 you needed to believe in souls in order to explain how you 32:41.338 --> 32:43.408 could have a person. 32:43.410 --> 32:46.510 But now Righty's a person without a soul, 32:46.509 --> 32:50.929 because we just hypothesized, oh, Shelly Kagan's soul's up 32:50.925 --> 32:54.355 there. So at the very same moment that 32:54.362 --> 32:59.522 positing the nonsplitting of souls seems to solve the fission 32:59.516 --> 33:03.736 problem of duplication, it yanks the rug out from 33:03.744 --> 33:08.694 underneath the soul theorist by undermining one of the types of 33:08.692 --> 33:13.322 arguments for believing in the soul in the first place. 33:13.319 --> 33:18.969 After all, if Righty can be a person, admittedly not Shelly 33:18.973 --> 33:24.053 Kagan, but a person--conscious, creative, rational, 33:24.053 --> 33:29.643 so forth, aware--without a soul, then maybe the same thing 33:29.644 --> 33:33.554 is true for us, which is of course what the 33:33.551 --> 33:34.981 physicalist says. 33:34.980 --> 33:38.030 Let me mention one other possibility, because it's quite 33:38.029 --> 33:41.209 intriguing. Suppose the soul theorist 33:41.210 --> 33:46.920 answers that last objection by saying, "Ain't ever going to 33:46.917 --> 33:50.347 happen." Yeah, it would be a problem for 33:50.348 --> 33:54.588 believing in souls if Righty could wake up without one. 33:54.589 --> 33:59.019 But since we stipulated that Shelly Kagan's soul is going to 33:59.017 --> 34:02.767 end up in Lefty, Righty is not going to wake up. 34:02.769 --> 34:06.819 Alternatively, it might have been that Righty 34:06.816 --> 34:11.776 woke up, but Lefty doesn't wake up, doesn't survive the 34:11.782 --> 34:14.982 operation. Suppose we did these sort of 34:14.975 --> 34:18.915 brain transfers all the time and the following thing always 34:18.923 --> 34:21.683 happened. Transfer the entire brain, 34:21.684 --> 34:23.334 the patient wakes up. 34:23.329 --> 34:27.679 Transfer one hemisphere, the patient wakes up. 34:27.679 --> 34:34.279 Transfer both hemispheres, one patient or the other wakes 34:34.283 --> 34:36.763 up, but never both. 34:36.760 --> 34:41.730 If that happened, we'd have a great new argument 34:41.728 --> 34:44.898 for the existence of a soul. 34:44.900 --> 34:48.590 What could possibly explain why either hemisphere of the brain 34:48.589 --> 34:51.799 would normally be enough, as long as we don't transfer 34:51.795 --> 34:53.375 both? When we transfer both, 34:53.376 --> 34:55.966 one hemisphere might work sometimes, sometimes the other 34:55.966 --> 34:57.376 hemisphere, but never both. 34:57.380 --> 35:00.470 What could possibly explain that? 35:00.470 --> 35:02.340 Souls could explain that. 35:02.340 --> 35:05.780 If souls can't split, it can only follow one half of 35:05.780 --> 35:09.690 the brain, and that's why we'll get somebody that's got one 35:09.692 --> 35:11.922 half, sometimes the other half, 35:11.919 --> 35:13.409 but never both halves. 35:13.409 --> 35:21.409 So there's a kind of empirical argument for the existence of 35:21.411 --> 35:27.651 the soul if we found those kinds of results. 35:27.650 --> 35:29.170 Of course, that's a big "if." 35:29.170 --> 35:31.290 Please don't go away thinking that what I just said is, 35:31.294 --> 35:32.754 here's a new argument for the soul. 35:32.750 --> 35:36.960 We don't do brain transfers, let alone have a half-a-brain 35:36.963 --> 35:39.513 transfers. We don't have any experiments 35:39.511 --> 35:42.721 that suggest one half wakes up, but not the other half. 35:42.719 --> 35:46.169 All I'm saying is that if someday we found that, 35:46.171 --> 35:49.331 at that point, we'd have an argument for the 35:49.329 --> 35:49.989 soul. 35:49.990 --> 35:57.910 35:57.909 --> 36:01.539 Well again, let me put away the soul theory again. 36:01.539 --> 36:03.749 I was exploring it because it's interesting to think about its 36:03.752 --> 36:06.142 implication. But since I don't believe in 36:06.141 --> 36:09.641 souls, I want to choose between the body view and the 36:09.635 --> 36:10.975 personality view. 36:10.980 --> 36:15.160 Both of them, as we saw in the face of 36:15.155 --> 36:20.455 fission, needs to accept a no branching rule. 36:20.460 --> 36:24.170 If they're going to survive thinking about this case at all, 36:24.169 --> 36:26.809 we need to throw in a no branching rule. 36:26.809 --> 36:30.889 Whether or not you find the no branching rule hard to believe, 36:30.887 --> 36:34.827 if both views are stuck with it, well, then we're stuck with 36:34.832 --> 36:37.902 it. So let's try to choose between 36:37.903 --> 36:43.203 the personality theory with the no branching rule and the body 36:43.198 --> 36:46.408 theory with the no branching rule. 36:46.410 --> 36:50.280 Which of these should we accept? 36:50.280 --> 36:56.330 Which of these is the better theory of personal identity? 36:56.330 --> 37:00.380 Answer, "I'm not sure." 37:00.380 --> 37:05.000 Over the course of my philosophical career, 37:05.004 --> 37:09.744 I have moved back and forth between them. 37:09.739 --> 37:13.559 There was certainly a long period of time in which I found 37:13.563 --> 37:17.673 the personality theory, that is, the personality theory 37:17.670 --> 37:21.590 with a no branching rule, to be the better and more 37:21.591 --> 37:23.161 plausible theory. 37:23.159 --> 37:27.989 And it certainly has any number of advocates on the contemporary 37:27.985 --> 37:29.665 philosophical scene. 37:29.670 --> 37:33.250 But at other times in my philosophical career, 37:33.246 --> 37:36.836 I have found the body theory, that is to say, 37:36.843 --> 37:40.023 the body theory with the no branching rule, 37:40.015 --> 37:42.655 to be the more plausible theory. 37:42.659 --> 37:47.379 And it is certainly the case that the body theory has its 37:47.375 --> 37:51.075 advocates among contemporary philosophers. 37:51.079 --> 37:54.469 For what it's worth--and I don't actually think that what 37:54.474 --> 37:57.994 I'm about to say is worth all that much--I'm going to share 37:57.990 --> 37:59.870 with you my own pet belief. 37:59.869 --> 38:05.089 These days I'm inclined to go with the body theory. 38:05.090 --> 38:08.790 I'm inclined to think that the key to personal identity is 38:08.787 --> 38:11.507 having the same body, as long as there's no 38:11.511 --> 38:14.561 branching, as long as there's no splitting. 38:14.559 --> 38:19.219 But it's certainly open to you to decide that you think no, 38:19.216 --> 38:23.226 no, the personality theory is the stronger view. 38:23.230 --> 38:25.050 I can't settle the question. 38:25.050 --> 38:28.680 I don't have any more philosophical arguments up my 38:28.680 --> 38:30.350 sleeve on this issue. 38:30.349 --> 38:37.759 But I do have another point that's worth considering. 38:37.760 --> 38:43.530 Although I'm inclined to think that the body theory may be the 38:43.531 --> 38:48.641 best view about what's the key to personal identity, 38:48.639 --> 38:54.149 I'm also inclined to think it doesn't really matter. 38:54.150 --> 38:58.200 38:58.199 --> 39:00.529 We've been posing the following question. 39:00.530 --> 39:06.270 We've been asking, "What does it take for it to be 39:06.273 --> 39:08.973 true that I survive?" 39:08.969 --> 39:11.949 And it may be that what we should conclude is, 39:11.948 --> 39:15.058 whatever the best answer to that question is, 39:15.059 --> 39:20.339 it's not the question we should really have been thinking about. 39:20.340 --> 39:22.810 We weren't going to be in a position to see that until we 39:22.806 --> 39:25.446 went through all the stuff we've been going over for the last 39:25.449 --> 39:28.029 couple of weeks. But now that we're here, 39:28.032 --> 39:31.512 we're in a position perhaps to raise the question, 39:31.508 --> 39:35.408 should we be asking what it takes to survive? 39:35.409 --> 39:43.259 Or should we be asking about what matters in survival? 39:43.260 --> 39:47.410 Now, in posing this question, I'm obviously presupposing that 39:47.406 --> 39:50.586 we can draw a distinction between the question, 39:50.585 --> 39:53.545 "Do I survive? Is somebody that exists in the 39:53.545 --> 39:54.855 future, whatever, me?" 39:54.860 --> 39:57.740 and the question, "What was it that I 39:57.744 --> 40:01.114 wanted, when I wanted to survive? 40:01.110 --> 40:07.350 What was it that mattered in ordinary survival?" 40:07.349 --> 40:11.249 And it might be that these things can actually come apart. 40:11.250 --> 40:14.740 To see this, suppose we start by thinking 40:14.744 --> 40:17.194 again about the soul view. 40:17.190 --> 40:19.470 Suppose there are souls. 40:19.469 --> 40:21.719 I don't believe in them, but let's imagine. 40:21.720 --> 40:23.180 Suppose there are souls. 40:23.179 --> 40:27.789 And suppose that souls are the key to personal identity. 40:27.789 --> 40:32.009 So somebody is me if they've got my soul. 40:32.010 --> 40:34.300 Or, to put it more straightforwardly, 40:34.301 --> 40:38.121 next week the person that's me is the person with my soul. 40:38.119 --> 40:40.999 I survive as long as there's somebody around with my soul. 40:41.000 --> 40:44.290 A hundred years from now, am I still around? 40:44.289 --> 40:46.809 Well, if my soul's still around, that's me. 40:46.809 --> 40:48.389 That's what the soul theory says. 40:48.390 --> 40:53.330 And suppose it's the truth. 40:53.329 --> 40:55.129 Now, consider the following possibility. 40:55.130 --> 40:59.890 Suppose that people can be reincarnated. 40:59.889 --> 41:03.159 That is to say, at the death of their body, 41:03.155 --> 41:06.335 their soul takes over, animates, inhabits, 41:06.344 --> 41:10.314 gets connected to a new body that's being born. 41:10.309 --> 41:13.659 But, unlike the kind of reincarnation cases that get 41:13.658 --> 41:17.728 talked about in popular culture and various religions where, 41:17.730 --> 41:20.270 at least under the right circumstances, 41:20.273 --> 41:24.093 you can remember your prior lives, let's imagine that when 41:24.088 --> 41:30.108 the soul is reincarnated, it's scrubbed completely clean, 41:30.106 --> 41:35.626 no traces whatsoever of the earlier life. 41:35.630 --> 41:37.300 No way to retrieve it. 41:37.300 --> 41:41.850 No karmic similarities of personality or anything, 41:41.845 --> 41:45.365 just starts over like a blank slate. 41:45.369 --> 41:48.159 Like a blackboard that's been completely erased, 41:48.160 --> 41:51.310 we now have the very same blackboard, and now we start 41:51.307 --> 41:53.027 writing new things on it. 41:53.030 --> 41:57.990 Imagine that that's the way reincarnation worked. 41:57.989 --> 42:01.029 So somebody asks you, "Will you still be around in 42:01.029 --> 42:03.329 1,000 years?" The answer's going to be, 42:03.327 --> 42:05.677 yes, because my soul will be reincarnated. 42:05.679 --> 42:08.649 In 1,000 years there'll be somebody that has the very same 42:08.650 --> 42:10.840 soul that's animating my body right now. 42:10.840 --> 42:14.230 Of course, that soul won't remember being Shelly Kagan. 42:14.230 --> 42:16.350 It won't have any memories of its prior life. 42:16.349 --> 42:20.809 It won't be like Shelly Kagan in any way in terms of Shelly 42:20.811 --> 42:24.581 Kagan's desires or ambitions or goals or fears. 42:24.579 --> 42:28.589 It won't be that--We can see why that personality emerges 42:28.592 --> 42:32.962 through karmic cause and effect in any way that are a function 42:32.963 --> 42:35.403 of what I was like in my life. 42:35.400 --> 42:39.640 It'll be Shelly Kagan, because it's Shelly Kagan's 42:39.639 --> 42:43.969 soul, but with no overlap of personality, memories, 42:43.965 --> 42:49.495 anything. Then I want to say, who cares? 42:49.500 --> 42:54.320 The fact that I will survive under those circumstances 42:54.323 --> 42:58.513 doesn't give me anything that matters to me. 42:58.510 --> 43:02.640 It's no comfort to me to be told I will survive, 43:02.640 --> 43:06.950 because after all, the soul is the key to personal 43:06.947 --> 43:10.007 identity, if there's no similar 43:10.007 --> 43:14.667 personality, no memories, no beliefs, no retrievable 43:14.665 --> 43:17.035 memories of past lives. 43:17.040 --> 43:20.820 Then who cares that it's me? 43:20.820 --> 43:23.450 If you can feel the force of that thought, 43:23.446 --> 43:26.966 then you're seeing how the question "Will I survive?" 43:26.969 --> 43:31.449 can be separated out from the question "What matters?" 43:31.450 --> 43:33.820 What do we care about? 43:33.820 --> 43:39.600 Bare survival of my soul, even though that is the key to 43:39.596 --> 43:45.056 personal identity--if it is--bare survival of my soul 43:45.058 --> 43:48.418 doesn't give me what I want. 43:48.420 --> 43:54.200 It's no more comforting or satisfying than if you said, 43:54.203 --> 43:57.313 "You know this knucklebone? 43:57.309 --> 44:00.609 After you die, we're going to do knucklebone 44:00.608 --> 44:04.748 surgery and implant that knucklebone in somebody else's 44:04.749 --> 44:06.889 body. And that knucklebone is going 44:06.889 --> 44:08.369 to survive." And I say, "Oh, 44:08.365 --> 44:11.605 that's very interesting that that knucklebone will be around 44:11.613 --> 44:13.323 100 or 1,000 years from now. 44:13.320 --> 44:18.940 But who cares?" And if the knucklebone theory 44:18.937 --> 44:22.227 of personal identity gets proposed and somebody said, 44:22.230 --> 44:24.840 "Oh, yes, but you see, that person now with that 44:24.843 --> 44:27.683 knucklebone will be you, because the key to personal 44:27.679 --> 44:30.459 identity is having the very same knucklebone." 44:30.460 --> 44:32.600 I say, "All right, so it's me. 44:32.600 --> 44:38.980 Who cares?" Bare knucklebone survival does 44:38.981 --> 44:42.051 not give me what matters. 44:42.050 --> 44:46.380 Now, the knucklebone theory of personal identity is a very 44:46.375 --> 44:48.695 stupid theory. In contrast, 44:48.697 --> 44:54.327 the soul theory of personal survival is not a stupid theory. 44:54.329 --> 45:00.439 But for all that, it doesn't give me what I want. 45:00.440 --> 45:05.690 When you think about the possibility of bare survival of 45:05.688 --> 45:08.738 the scrubbed, clean, erased soul, 45:08.742 --> 45:14.662 you see that survival wasn't really everything you wanted. 45:14.659 --> 45:18.679 What you wanted--at least what I want, I invite you to ask 45:18.675 --> 45:22.825 yourself whether you want the same thing--what I want is not 45:22.831 --> 45:25.741 just survival, but survival with the same 45:25.739 --> 45:26.999 personality. 45:27.000 --> 45:30.760 45:30.760 --> 45:33.970 So even if the soul theory is the correct theory of 45:33.969 --> 45:37.499 personality, it's not enough to give me what matters. 45:37.500 --> 45:39.700 What matters isn't just survival. 45:39.699 --> 45:44.819 It's survival with the same personality. 45:44.820 --> 45:45.820 Let's consider the body view. 45:45.820 --> 45:50.070 45:50.070 --> 45:55.750 Suppose that the body theory of personal identity is correct. 45:55.750 --> 45:57.890 And to be me, there's got to be somebody 45:57.889 --> 45:59.369 there that's got my body. 45:59.369 --> 46:01.819 Let's suppose the brain version of the theory is the best 46:01.822 --> 46:04.272 version. And so next year, 46:04.269 --> 46:10.179 there's going to be somebody that's got my brain. 46:10.179 --> 46:14.759 But let's imagine that the brain has been scrubbed clean. 46:14.760 --> 46:19.310 All memory traces have been completely erased. 46:19.309 --> 46:24.719 We're talking complete irreversible amnesia, 46:24.724 --> 46:30.394 complete erasure of the brain's hard drive. 46:30.389 --> 46:34.869 No traces of desires and memories and intentions and 46:34.871 --> 46:39.531 beliefs to eventually be recovered if only we have the 46:39.528 --> 46:41.778 right surgery, or procedure, 46:41.778 --> 46:43.628 or psychotherapy, or what have you. 46:43.630 --> 46:48.180 It's gone. Now, that thing that wakes up 46:48.183 --> 46:52.833 after this complete irreversible amnesia will no doubt eventually 46:52.825 --> 46:55.645 develop a personality, a set of beliefs, 46:55.654 --> 46:57.654 memories. Nobody knows who it is, 46:57.651 --> 46:59.571 so they call it, they find it wandering on the 46:59.570 --> 47:02.860 streets. They call it John Doe. 47:02.860 --> 47:06.920 John Doe will eventually have a bunch of beliefs about how the 47:06.915 --> 47:10.235 world works, make some plans, get some memories. 47:10.239 --> 47:13.509 According to the body theory, that's me. 47:13.510 --> 47:17.240 47:17.239 --> 47:20.719 And if the body theory is correct, well by golly, 47:20.722 --> 47:23.802 it is me. And all I can say in response 47:23.795 --> 47:26.615 to that is, it's me, but who cares? 47:26.620 --> 47:31.430 So what? I'm not comforted by the 47:31.434 --> 47:37.304 thought that I will still be around 50 years from now, 47:37.297 --> 47:43.267 if the thing that's me doesn't have my personality. 47:43.269 --> 47:51.419 Mere bodily survival isn't enough to give me what I want. 47:51.420 --> 47:55.830 I want more than mere bodily survival. 47:55.829 --> 48:03.559 I want to survive with the same personality. 48:03.559 --> 48:07.519 So even if the body theory of personal identity is the right 48:07.520 --> 48:10.810 theory, what I want to say in response to that is, 48:10.810 --> 48:14.240 "So what?" If the really crucial question 48:14.238 --> 48:19.548 is not "Do I survive," but "Do I have what I wanted when I wanted 48:19.545 --> 48:23.725 to survive?" the answer is the body theory 48:23.727 --> 48:27.157 doesn't give it. I don't just want to survive. 48:27.159 --> 48:32.879 I want to survive with the same personality. 48:32.880 --> 48:38.300 Should we conclude, therefore, that the key to the 48:38.301 --> 48:44.161 important question--namely, "What matters?"--the answer to 48:44.161 --> 48:47.081 that question, should we conclude, 48:47.078 --> 48:49.198 is, same personality? 48:49.199 --> 48:51.999 That's a question we'll have to take up next time.