耶魯大學(xué)開放課程——哲學(xué)：死亡Death 5

    Death: Lecture 5 Transcript

    January 30, 2007

    Professor Shelly Kagan: All right. We've been talking about arguments that might give us reason to believe in the existence of an immaterial soul. The kinds of arguments we've been considering so far all fall under the general rubric of "inference to the best explanation." We posit--or the fans of souls posit--the existence of souls so as to explain something that needs explaining about us. I've gone through a series of such arguments, and the one that we ended with last time was the suggestion that we need to believe in the existence of a soul in order to explain the fact that we've got free will. The fact that we've got free will is something that most of us take for granted about ourselves. But the complaint then, or the objection to the physicalist, takes the form that we couldn't be a merely physical entity because no merely physical entity could have free will. But we've got free will, so there's got to be something more to us than just being a physical object. Now, if we push the dualist to explain what is it about free will that rules out the possibility that we are merely physical objects, I think the natural suggestion to spell out the argument goes like this, and this is where we were at the end of last time.

    The thought is that, there's a kind of incompatibility with being free and being determined. I mean, after all from the physicalist's point of view, we're just a kind of glorified robot, able to do all sorts of things that most robots in most science fiction movies can do. But still, in a sense, we're just a glorified physical object. We're just a robot. And robots, the objection goes, are programmed; they necessarily follow their program. More generally speaking, we might say, they're subject to deterministic laws--that, as physical objects, it's true of them that they must do what the laws of physics and laws of nature require that they do. And the laws of physics are--take a deterministic form, determinism being a bit of philosopher's jargon for when it's true of these laws that--or a physical--or a system--that if you set it up a certain way, cause and effect plays out such that, given that initial setup, the very same effect must follow. It's determined by the laws of nature that the effect that follows will follow from that cause. And so, if you rewind the tape and play it again over and over and over again, each time you set things up the very same way they must move or transform or change or end up in the very same state. Well, that's what determinism is all about.

    And intuitively, it seems plausible to many people that you couldn't have free will and be subject to determinism. Because the notion of free will was that even if I was in the very same spot again, the very same situation again, I could've chosen differently. So I wasn't determined or predetermined to make that choice. So if we were to spell out the argument somewhat more fully, it might be, "We have free will, but you can't both have free will and be subject to determinism or subject to deterministic laws." And every physical object, or every purely physical object, is subject to deterministic laws because the laws of physics are deterministic. You put these things together and you get the conclusion that we, since we've got free will, can't be a purely physical object. There must be something more than the purely physical to us.

    That's the argument I put up on the board at the end of last class. And here we've got it up here now. [See Figure 5.1] One, we have free will. Two, nothing subject to determinism has free will. Three, all purely physical systems are subject to determinism. So--a conclusion--we are not a purely physical system. To explain the fact that we've got free will, so the objection goes, we have to appeal to--we have to posit--the existence of a soul, something non-physical, something more than purely physical. Well, that's the argument. But I don't myself find the argument compelling. Now, the first thing to notice is that to get the conclusion we need all three premises. Give up the conclusion that we've got--Give up the premise that "we've got free will," it won't follow that we're non-physical. Even if something that did have free will would have to be non-physical, it wouldn't follow that we're non-physical. That's true for each one of the premises. Give it up, the conclusion doesn't go through. And the interesting thing is that each one of these premises could be plausibly challenged.

    Now, as I said last time, the subject of free will--or free will, determinism, causation and responsibility, this cluster of problems--is an extremely difficult and complicated physical problem. And we could easily devote an entire semester to discussing it. So all we're doing here is the most quick and superficial glance. But still, let me quickly point out why you could resist the argument from free will to the existence of a soul. First of all, as I just noted, the argument needs premise number one. It's got to be the case, to prove that we've got a soul--at least for this argument to work to prove that we've got a soul--it's got to be the case that we've got free will.

    Now, that could be challenged. There are philosophers who have said we certainly believe that we've got free will, but it's an illusion. We don't really have free will. Indeed, why don't we have free will? For precisely the reasons that are pointed to by the rest of the argument. They might say, "Oh, well, you know, we're physical objects; determinism is true of us. No physical object that's subject to determinism could have free will, so we don't have free will. Of course, we mistakenly believe we've got free will. We are physical objects that labor under the illusion that we have free will, but after all, free will isn't something that you can just see, right? You can't peer into your mind and see the fact that you've got free will. Yes, we've got the sense that we could've acted differently, but maybe that's an illusion." As I say, there are philosophers who've argued that way, have denied that we have free will and if we do conclude that we don't actually have free will, then we no longer have this argument for the existence of a soul. It's a way to avoid the argument; although, for what it's worth, I should mention I don't myself believe that it's false that we have free will. That is to say, I do think premise one is true. I myself think we do have free will. So although I don't like, I don't believe the argument is sound--premise one doesn't happen to be the premise I myself would want to reject.

    But there are other, there are two other key premises. What about premise number three, "All purely physical systems are subject to determinism." Well, we need that premise as well to make the argument go. Suppose we think, "Look, you can't have free will and determinism. You can't combine them." The view that you can't combine them is sometimes known as "incompatibilism" for the obvious reason. It's the view that these two things are incompatible. You can't have determinism and free will. Suppose we do believe in incompatibilism and believe that we've got free will. It would follow then that we're not subject to deterministic laws. Well, the dualist says, "That shows us that we have to believe that there's something non-physical about us. Because after all, premise three: ‘All purely physical systems are subject to determinism.' Isn't it true after all that the basic laws of physics are deterministic laws?" And the answer is, "Well it's not so clear that it is true." Which is just to say that premise three of the argument can be rejected as well.!

    Now, at this point I have to just confess, as I've confessed at other times before, three is a claim about empirical science. What does our best theory about the laws of nature tell us? And I'm no scientist and I'm no specialist in sort of empirical matters, and believe me, I'm no authority on quantum mechanics, our best theory of fundamental physics. Still, I take it--I gather--here's what I'm told--that the standard interpretation of quantum mechanics says that, despite what many of us might've otherwise believed, the fundamental laws of physics are not, in fact, deterministic.

    What does that mean? Suppose we've got some sort of radioactive atom, which has a certain chance of decaying. What does that mean? Well, it means that, you know, there's maybe, let's say, an 80 percent chance that in the next 24 hours it will break down. Eighty percent of atoms that are set up like that break down in the next 24 hours; 20 percent of them don't. Now, according to quantum mechanics under the standard interpretation, that's all there is to say about it. You have an atom like that, 80 percent chance in the next 24 hours it will break down.

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    Suppose it does break down! Can we say why it broke down? Sure. We can say, "Well, after all there was an 80 percent chance that it would." Take an atom that after 24 hours hasn't broken down. Can we say why it hasn't broken down? Sure. There was a 20 percent chance that it wouldn't. Can we explain why the ones that do break down break down and the ones that don't break down don't break down? No. All we can say is, there was an 80 percent chance it would, 20 percent chance it wouldn't, so most of them do, some of them don't. That's as deep as the explanation goes. There is nothing more. Now, you know, when we've got our deterministic hats on, we think to ourselves, "There's got to be some underlying causal explanation, some feature about the break-down atoms that explains why they broke down and that was missing from the non-break-down atoms that explains why they don't break down. After all, determinism, right? If you set up the atoms exactly the same way, they've always got to break down." But the answer is, according to the standard interpretation of quantum mechanics, that's not how it works. All there is to say is, "Some of these are going to break down, and some of these won't."

    The fundamental laws of physics, according to the standard interpretation of quantum mechanics, are probabilistic. Determinism is not true at the level of fundamental physics. Well, that's what I'm told. Believe me, I'm in no position to say, but that's what I'm told. And of course, if that's true, then premise three is false. It just isn't true that all purely physical systems are subject to determinism. So even if it does turn out that you can't have free will and determinism, that doesn't rule out the possibility that we are purely physical objects, because not all purely physical systems are subject to determinism. If determinism isn't true of us at the fundamental level, then even if you couldn't both have determinism and free will, we could still have free will, and yet, for all that, still be purely physical systems.

    While I'm busy pointing out ways in which the argument doesn't succeed, I also want to just take a moment and mention that premise two is also subject to criticism. Premise two was the incompatibilist claim that, "nothing subject to determinism has free will." You can't combine them. They're incompatible. Now, incompatibilism, I take it, is probably something like the common-sense view here. It's the view that probably most of you believe, but again, it's worth noting that philosophically it can be challenged. There are philosophers--and here I'll tip my hat and say, I'm one of them--there are philosophers who believe that, in fact, the idea of free will is not incompatible with determinism. So even if determinism were true of us, that wouldn't rule out our having free will, because you can--appearances to the contrary notwithstanding--have both determinism and free will. They're compatible. Hence, this view is known as compatibilism.

    If we accept compatibilism, we'll be able to say, "Look, maybe we have free will and determinism is true of us; but for all that, we're still just purely physical systems." Even if quantum mechanics was wrong and somehow, you know, at the macro level all the indeterminism boils out--whatever--and at the macro level we are deterministic systems, so what? If a deterministic system could nonetheless have free will, we could still be purely physical systems. Now, mind you, I haven't said anything today to convince you of the truth of compatibilism, nor am I going to try to do that. My point here was only to say we shouldn't be so quick to think that we have to believe in the existence of a soul in order to explain our having free will. It takes all of the premises of the argument to get the conclusion that the soul exists. And each one of the premises can be challenged. And here I mean not merely, well, logically speaking, you know, of course you can reject any premise of any argument. No. I mean, there are reasonable philosophical or scientific grounds for worrying about each one of the premises. The argument requires a lot. That doesn't prove that the argument fails, but it does mean that you're going to have your work cut out for you if you're going to use this route to arguing for the existence of a soul.

    All right. Let's recap. As I said, we've been considering different kinds of arguments for the existence of a soul, each of which appeals to some feature about us--our creativity, our ability to feel, the fact that we have a qualitative aspect of experience, our ability to reason--what have you. Some fact about us that calls out for explanation, and the claim on the part of the dualists was, we couldn't explain it without appealing to a soul. And I've argued--I've shared with you my reasons for thinking that those arguments are not compelling. But notice that all of the kinds of considerations I pointed to so far are what we might think of as everyday, familiar features about us. It's an everyday occurrence that we can think and reason and feel and be creative, or choose otherwise and have free will.

    Maybe the better arguments for the soul focus not on the everyday but on the unusual, on the supernatural. Here we might then have an entire other family of arguments, set of arguments--again, still of the form "inference to the best explanation." Maybe we need to posit the soul in order to explain ghosts. Maybe we need to posit the soul in order to explain ESP; maybe we need to posit the soul in order to explain near-death experiences. Maybe we need to posit the soul in order to explain what goes on in séances or communications from the dead or what have you. For any one of those, we could again run an argument where we say, "Look, here is something that needs explaining. The best explanation appeals to the soul."

    Now, I'm going to be rather quicker in discussing this family of arguments, but let me take at least a couple of minutes and do something about that. Take, for example, near-death experiences. This is something that you read a bit about in the selection from Schick and Vaughn [Schick and Vaughn 2005, 207-323] in your course packet. The basic idea was probably familiar to most of you anyway, that the following thing happens with people who, you know, maybe their heart goes into a cardiac arrest--what have you. They die on the operating table, but then they're brought back to life, as we put it. And many such people, when we question them afterwards, have a very striking experience. And one of the things that's striking is, how similar the experience is from person to person and from culture to culture--that they've got some notion, as they were dead on the operating table, of leaving their body. Perhaps they begin to view their body from up--floating up above it. Eventually, perhaps, they leave the operating room altogether in this experience that they're having, and they have a feeling of joy and euphoria; they have some experience of going through a tunnel, seeing some light at the end of the tunnel. Perhaps at the other end of the tunnel they begin to have some communications or see some loved one who has died previously or perhaps some famous religious person in their--in the teaching of their tradition--their religious tradition. They have the sense that what they've done is basically died and gone to heaven. But then suddenly they get yanked back, and they wake up, you know, in the hospital room. So they've had near-death experiences. Or perhaps a better way to put it would be they've had death experiences but then have been brought back to life.

    Now, there it is, right? You survey people, and people have these experiences. And now we have to ask ourselves, "What explains this?" And here's a perfectly straightforward and natural explanation. These people died. Their bodies died, and they went to the next world. They went to the next life. They went to heaven but then were yanked back. Now, their bodies were lying there on the operating table; their bodies weren't in heaven. So something non-bodily went to heaven. That's how the explanation goes. It's a natural, straightforward explanation of what's gone on here. Hence, inference to the best explanation. We need to posit the soul, something immaterial that survives the death of the body, that can leave the body, go up to heaven; though, as it happens in these cases, the tie is never completely broken. They get yanked back; the soul gets yanked back by whatever cause, and reconnected to the body.

    It's as though we might think of there being two rooms, to use a kind of analogy here. There is the room that this world represents, this life represents. And what happens in these experiences is that your soul leaves this room and goes into a second room, the room of the next world or the next life, but for various reasons, isn't allowed to stay in the next room. It gets yanked back to this room.,

    Well, that's a possible explanation. And in a moment, I'll ask whether it's the best possible explanation, but before we do turn to that question, there is an objection to this entire way of looking at things that's probably worth pausing for a moment and considering. The objection is similar to the kind of dismissive attitude that we saw at the beginning of the course about the question, "Could I survive my death?" Well, duh. Could there be life after there is no more life? Well, of course not.!

    Here the objection says, this two-room notion's got to be mistaken. It can't be that what's going on in near-death experiences is that people are reporting about what it's like to be dead because--so the objection says--they never really died. After all, 20 minutes later, or whatever it is, there they are up and about. Well, not up and about; they're presumably lying in their hospital beds, but they're clearly alive. Hence, it follows that they never really died. Or, if you want, you could say maybe they died, but since they obviously didn't die permanently--after all they were brought back to life--how could they possibly tell us what it's like to be permanently dead? How can we take their experiences as veridical reports of the afterlife? Because what we want to know is what is like to be permanently dead, and these people were never permanently dead. So whatever unusual experiences they may be having, they are not reports of the afterlife. That's how the objection goes.

    Although, I think, I was pausing for a moment to raise that objection, it's not an objection that I think we should take all that seriously. Suppose we were to agree, all right, strictly speaking these people didn't die. Or strictly speaking they didn't die, certainly at least, permanently. Does it follow from that that their experiences should not be taken as evidence of what the afterlife is like? I think that's really a misguided objection. Suppose somebody said, "Look, I spent 20 years living in France, and then I came back to the United States. And so I want to tell you what it's like in France." And somebody says, "You know, you never really moved to France permanently. So your experiences in France, whatever they are--interesting as they may be--can't really cast any light on what it would be like to permanently move to France. You'd say, "Give me a break!" Right? "It's true that, of course, I didn't move to France permanently. Still, I have some experience of France. And so I can--a great deal after all, 20 years--I can give you a pretty good idea of what it's like to live in France, even if I didn't move there for the rest of my life without ever coming back." You can't say quite as much if you've only been in France for a couple of days before coming back, but still you can say something relevant.

    

    Indeed, suppose I never went into France at all. Suppose all that happened was I stood right on the border and peered into France, talked to some people in France. They were on the French side of the border, I was on the other side, but I talked to them for a while. Still, I never went in, but for all that I might have something helpful to say about what it's like in France. Well, if that's the right thing to say about the France case, then why not say the same thing about the near-death experience case? Even if these people didn't stay in the second room, they didn't stay dead, they had some experience of being dead. Isn't that relevant to what it would be like to be dead? Or even if we say, "No. Strictly speaking, these people didn't die at all. They were just on the border looking in. They never, strictly speaking, died at all." So what? They were on the border looking in. To suggest that that couldn't be relevant evidence is like saying I can't tell you anything interesting about what's going on in the hallway right now, because after all I'm not in the hallway; I'm here in the lecture hall. So what? Even though I'm here in the lecture hall, I can see into the hallway and tell you what's going on in it.

    So attempts to dismiss the appeal to near-death experiences on what we might call philosophical grounds--this would be the bad notion of philosophy--on philosophical grounds, I think that's got to be misguided. Still, that doesn't mean that we should believe the argument for the existence of the soul from near-death experiences, because the question remains, "What's the best explanation of what's going on in near-death experiences?" Now, one possibility, as I suggested, was what I called a second ago the "two-room explanation." There's the room of this life, and there's the room of the next life and people who have near-death experiences either temporarily were in the second room or else at least they were glancing into the second room. That's one possible explanation. But of course, there's a different possible explanation--the one-room explanation. There's just life, this life, and as you come very close to the wall of the room, things end up looking and seeming and feeling rather different than they do in the middle of the room.

    Now, maybe the one-room metaphor is not the best metaphor, because it immediately prompts the question, "Well, what's on the other side of the wall?" And of course, the physicalist's suggestion is there isn't anything on the other side of the wall. So maybe a better way to talk about it would just be: Life's a biological process; we're all familiar with that process, sort of, in its middle stretches. In its closing stretches, some fairly unusual biological processes kick in. In rare, but not unheard of, cases, some people begin to have those unusual biological processes and then return to the normal biological processes and can talk about what was happening in the unusual biological processes. Which is just to say, we need to offer a biological/physical explanation of what goes on in near-death experiences.

    Now, mind you, that's not yet to offer the physical explanation; it's just a promissory note. We now have two rival explanations, the soul, dualist, explanation that we went into the other world and the physicalist, promissory note that we can explain the white lights and the feeling of euphoria and seeing your body from a distance in physical terms. We don't really have very much of a physical explanation until we begin to offer scientific accounts of each of those aspects of near-death experience. But this is, in fact, an area on which scientists work. And you saw some of the beginnings of an explanation offered in the reading by Schick and Vaughn. So, for example, when the body is in stress, as would likely happen toward the end of the biological processes, when the body is in stress, certain endorphins get released by the body. Perhaps that explains the feelings of euphoria. When the body is in stress, we have various unusual stimulations of the visual sections of the brain, and perhaps that explains the white light or the feeling of compression in the tunnel.

    Now, again, I'm not any kind of scientist and so I'm not in any position to say, "Look, here are the details of the explanation." But you get the beginnings of that sketched in the readings, and it's a judgment call you've got to make. Does it seem more plausible that we can explain these experiences in terms of the traumatic stress that your body and brain is going through when you are near dying? Or is it more plausible to suggest, "No. What's happened here is a soul has been released from connection with the body." For my money, I find the beginnings of the scientific explanation sufficiently persuasive and sufficiently compelling that I don't find the argument from near-death experience--as an argument for the existence of a soul--I don't find it especially persuasive.

    Of course, there are various other things we could appeal to in terms of supernatural occurrences, right? I've only mentioned--only discussed now in detail--one of them. But there are a variety of things about people who can communicate from the dead or ghosts or séances or what have you. And what the physicalist would need to do for each one of those--For each one of those you can imagine a dualist who says, "We need to believe in a soul so as to explain séances. How do we explain the fact that the person who's conducting the séance knows things about, your history that only your dead uncle would know?" The dualist can explain that by appealing to ghosts and the like.

    How does the physicalist explain things like that? Short answer is, I don't know. I'm not the kind of person who makes it his business to try to explain away those things in physicalist, naturalistic, materialistic, scientific terms. But there are people who make it their business. So, for example, there's a magician--The question is not, could I explain to you how the séance manages to do the amazing things that it does? You're wasting your time asking somebody like me. The person to ask is a magician, somebody whose profession it is to fool people and make it look like they can do things with magic. So in fact, there are professional magicians who make it their business to debunk people who claim to genuinely be in contact with the dead and the like. There's a magician, I think his name is The Amazing Randi, who has a sort of standing offer; he says, "You show me what happened in the séance or in communication with the dead or what have you, and I'll show you how to do it. I'll debunk it for you." Spoiler alert. And he has a standing offer, he says, "I'll pay whatever the amount is, $10,000 to the first person who can document some effect done in supernatural terms that I can't reproduce through trickery." So far he's never had to pay out.

    Well again, that doesn't prove the dualist is wrong. It could be that there are genuine séances. It could be that there really are ghosts. It could be that there really is communication from the dead. As is typically the case, you've got to decide for yourself what strikes you as the better explanation. Is the supernatural, dualist explanation the more likely one? Or is the physicalist explanation the more likely one?

    Look, you have a dream where your dead mother has come back to talk to you. One possible explanation, the dualist, that's the ghost of your mother, immaterial soul that she is, communicating to you while you're asleep. Second possible explanation, it's just a dream. Of course you dream about your mother because your unconscious cares about her. What's the better explanation? We don't have the time here to go case, by case, by case, and ask ourselves, "How does the evidence fall down one side versus the other?" But when I review the evidence, I come away thinking there's no good reason to move beyond the physical.

    So again, let's recap. One group of arguments for the existence of a soul says, "We need to posit a soul in order to explain something, whether it's something everyday or something supernatural." The existence of a soul would be the beginnings of a possible explanation. But the question is never, "Is that a possible explanation?" but, "Is it the best explanation?" And when I review these various arguments, I come away thinking the better explanation falls with the physicalist. Mind you, I don't want to deny that there are some things the physicalist has not yet done a very compelling job of explaining. In particular, as I've mentioned previously, I think there are mysteries and puzzles about the nature of consciousness, the qualitative aspect of experience, what it's like to smell coffee or taste pineapple or see red. It's very hard to see how you explain that in physicalist terms. So to that extent, I think we can say the jury may still be out. But I don't think what we should say is, "The better explanation lies with the dualist." Because I think positing a soul doesn't really yet offer us the explanation. It just holds out the promise of an explanation. So at best that's a tie, and hence, no compelling reason to accept the existence of a soul.

    It would be one thing if we could see that no conceivable physicalist explanation could possibly work. But I don't think we're in that situation. All we're in right now is, perhaps in existence of that with regard to consciousness, maybe some other things, we don't yet see how to explain it. But not yet seeing how to explain it is not the same thing as seeing that it can't be explained on physicalist terms. Of course, again, if we had a dualist explanation with some details really worked out, maybe we'd have to say, "Look, this is the better explanation." But dualism doesn't so much offer the explanation typically as just say, "Well, maybe we'd be better off positing something immaterial." That, I think, is not a very compelling argument.

    Well, let's ask. What other kinds of arguments could be offered for the existence of a soul? I want to emphasize the point that the various arguments that I have been talking about so far, although they have this common strand--"inference to the best explanation"--are each separate and distinct arguments. One of them might work even though the other ones don't work. But I want to turn now to a rather different kind of argument..

    The argument I'm about to sketch is a purely philosophical argument, not really so much a matter of who can explain this or that feature of us better than anybody else. It's an argument that doesn't seem to have any empirical premises; it works from purely armchair philosophical reflection. And the striking thing is that many people find this a pretty compelling argument. The argument I'm going to give traces back to Descartes, the great early modern philosopher. Well, I'm not going to follow the details of this argument, but the basic idea goes back to Descartes. And it starts by asking you to imagine a story.

    So I'm going to tell the story in the first person. I'm going to tell about myself, but you know, you'll find the argument sort of, perhaps more persuasive if, as I tell the story, you imagine the story being told about you. So each one of you should translate this into a story about yourself. You know, your morning. So this is a story about my morning. Imagine--this didn't, of course, actually happen, but imagine--the crucial point here is simply that we can imagine this story happening, not even that we think it's empirically possible, just it's conceivable, it's an imaginable story. All right.

    So suppose that I woke up this morning, that is to say, at a certain point I look around my room and I see the familiar sights of my darkened bedroom. I hear, perhaps, the sounds of the cars outside my house, my alarm clock ringing, what have you. I move out of the room toward the bathroom, planning to brush my teeth. As I enter the bathroom, it's much more light, I look in the mirror and--here's where things get really weird--I don't see anything. Normally, of course, when I look in the mirror I see my face. I see my head; I see the reflection of my torso. But now, as I'm looking into the mirror, I don't see anything at all. Instead, I see the shower reflected behind me. Normally, that's blocked of course by me, by my body. But I don't see my body. Slightly freaked out, I reach for my head, or perhaps we should say I reach for where I would expect my head to be, but I don't feel anything there. Glancing down at my arms, I don't see any arms. Now, I'm really panicking. As I begin trying to touch my body, I don't feel anything. I don't--Not only can't I feel anything with my fingers, I don't have any sensations where my body should be.

    Now, we could continue this story, but I've probably said enough for you to grant that what I've just started doing--a novelist could do a better job of telling the story than I just did--but what I've just done was basically imagine--I've imagined a story in which I discover that my body doesn't exist. Or I've imagined a story in which my body has perhaps ceased to exist, or I've imagined a story in which I exist, or at least my mind exists. You know, I'm thinking thoughts like, "Why can't I see my body in the mirror? Why can't I feel my head? What's going on?" I'm panicking, right? We've got a story in which I'm thinking all sorts of thoughts; my mind clearly exists, and yet, for all that, my body does not exist. We could--certainly it seems--imagine that possibility. Now, the brilliant thing about this argument is it goes from that to a conclusion about there being a difference between my mind and my body.

    What we've just done, after all, is imagine that my mind exists but my body does not. Now, what does that show? Descartes says what it shows is the mind and the body must be two logically distinct things. The mind and the body cannot be the same thing. Because, after all, what I just did was imagine my mind existing without my body. How could I even do that, even in imagination? How could it even be possible to imagine my mind without my body, if talking about my mind is just a way of talking about my body? If they're really, bottom line, metaphysically speaking, the same thing, then you couldn't have one without the other after all. So here's a podium. Try to tell a story in which this podium exists but this podium does not exist. You can't do it, right? The podium is just one thing, the podium. And if it is just one thing, you could tell a story in which it exists; you could tell a story in which it doesn't exist. But you can't tell a story in which it exists and doesn't exist.

    If I can tell a story in which A exists and B doesn't exist, it's got to follow that A and B are not the same thing. Because if B was just another word for, another way of talking about, A, then to imagine A existing but B not existing would be imagining A existing but--well, B is just A--A not existing. But of course, you can't imagine a world in which A exists but A doesn't exist. Put the same point the other way around: If I can imagine A without B, then A and B have to be logically distinct things. They cannot be identical. But since I can imagine my mind existing without my body, it follows that my mind and my body have to be logically distinct things. They cannot be identical. My mind cannot just be a way of talking. Talking about my mind cannot just be a way of talking about my body.

    Now, it's a very cool argument. You know, philosophers love this argument. And I've got to tell you, to this day there's a debate in the philosophical community about whether or not this argument works. It's one thing to be clear--a couple of things to be clear about. What exactly is this argument not doing? The argument is not saying, "If something is possible, if I can imagine it, it's true." No. I can imagine unicorns. It doesn't mean unicorns exist. That's not what the argument is saying. The argument is only making a much more specific claim. If I can imagine one thing without the other, they must be separate things. Now, of course, it could still be that in the real world the one thing cannot exist without the other. There may be some sort of metaphysical laws that tie the two things so tightly together that you'll never actually get one without the other. That's not the question. The point is just if I can at least imagine the one thing without the other, they must in fact be two separate things. Because if there was really just one thing there, you couldn't imagine it without it. Since I can imagine my mind without my body, it must be the case that my mind is something separate and distinct from my body. Otherwise, how could I imagine it existing without the body? If they were the same thing, I couldn't--I can't imagine the body existing without the body. If the mind is just a way of talking about the body, how could I imagine the mind without the body? Since I can imagine the mind without the body, it follows that they're separate. So the mind is not the body after all. It's something different. It's the soul.

    Is that a good argument or not? That's where we'll start next time.