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PH1102E Week 11 Knowledge I. A skeptical argument II. A question of proof III. Phenomenalism

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I. A skeptical argument Consider the following argument: (1) A mental life just like yours -- same thoughts, sensations, feelings, moods, desires, etc. --

could exist in a world in which nothing else existed. (In other words: a universe consisting of nothing but a mental life just like yours is possible.)

(2) If a universe consisting of nothing but a mental life just like yours is possible, then you can’t

know whether the actual universe -- the reality that you actually inhabit -- isn’t just such a universe.

(3) Therefore, you can’t know whether anything exists except your own mental life. The conclusion of this argument -- that you can’t know whether reality contains anything besides your own mental life -- is called skepticism about the external world. There are two ways to interpret the skeptical argument. On one hand, we could interpret it as an attempt to prove that you can’t know whether there exists anything but your own mind and its contents. Interpreted this way, it is hard to see the argument as anything but an abject failure. Certainly the argument is not going to convince anyone that he doesn’t know whether there are things besides his own conscious mental states. Not even someone who puts forward the skeptical argument with the stated intention of converting people to skepticism believes that the argument succeeds as a proof, since not even such a person accepts the conclusion of the argument, unless perhaps he is insane and really does doubt that he has a body, or that there are such things as birds and trees. Anyway, no sane person among us will be swayed by the skeptical argument. Whether an argument that has no possibility of convincing sane people of its conclusion can be considered a “proof” in some technical sense unrelated to the power to convince is a question we may set aside as uninteresting. A proof interests us only to the extent that it proves something to us, or at least to some non-insane individual. It seems to me that a better way to interpret the skeptical argument is as a paradox. A “paradox” is a conclusion whose premises seem true, and seem to lead inevitably to the conclusion, but whose conclusion seems false. Interpreted as a paradox, the skeptical argument is not an attempt to prove that we don’t know whether there is an external world. It is not a threat to our knowledge, but a puzzle to be solved. In the next section of these notes, I’ll try to convince you that this is, indeed, the correct way to approach the skeptical argument. Then, in Section III, we’ll consider a possible solution to the skeptical puzzle.

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II. A question of proof Anti-skeptic: Why should I accept (2)? I mean, suppose I grant that there could be a universe consisting entirely of a mental life just like my own mental life. How does it follow that I don’t know that the actual universe -- the reality in which I actually live -- is not like that? Skeptic: Because if a universe consisting of nothing but a mental life just like yours is possible, you have no way of proving that the actual universe is not precisely such a universe! Anti-skeptic: So what? I mean, suppose I can’t prove that the universe contains anything but my own mental life. How does it follow from that that I don’t know that the universe contains things besides my own mental life? Skeptic: Well, if you can’t prove something, how can you know it? Anti-skeptic: You think that a person knows only what he can prove? Skeptic: Yes. Anti-skeptic: Do you know that 1+2=3? Skeptic: Of course. Anti-skeptic: Prove it. Skeptic: Um... Anti-skeptic: I suppose you also know that you exist? Skeptic: Yes, and I can also prove it with the following argument: I think; therefore, I am. Anti-skeptic: That’s no proof. You’re simply begging the question. You’ve already assumed your own existence with the premise “I think.” Any other suggestions? Skeptic: Uh.... Anti-skeptic: So it seems that you do know things that you can’t prove. Skeptic: Well, maybe you’re right. But still, these are very simple things that it’s really impossible to doubt. “There is an external world,” however, is not like “I exist” or “1+2=3.” Granted that I know that I exist, and that 1+2=3, despite being unable to prove these things, still, I can’t know that there is an external world unless I can prove that there is an external world. “There is an external world” is more like “I have ten dollars in my pocket.” If I can’t prove that I have ten

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dollars in my pocket, then I don’t know that I have ten dollars in my pocket. Likewise, if I can’t prove that there’s an external world, then I don’t know that there’s an external world. Anti-skeptic: Couldn’t I know that I had ten dollars in my pocket even if I were bound and gagged, and in various other ways prevented from proving it? Skeptic: Maybe; but at least you’d know how you could go about proving that you had ten dollars in your pocket, given the opportunity to do so. But you have no idea how to prove that there is an external world. Anti-skeptic: You say that even if I were tied up etc., I would still know how to prove that I had ten dollars -- it’s just that I wouldn’t be able to carry out the proof in practice, due to my restraints. I assume what you have in mind is that if I were untied, I could reach into my pocket and produce a ten dollar bill, thereby proving that I did have ten dollars in my pocket? Skeptic: Yes, that’s one way you could prove it. Anti-skeptic: But what if I am a disembodied spirit under the control of an evil demon? Or what if I’m trapped in a grand dream or hallucination? Or what if I am a brain in a vat? According to you, I can’t prove that these things aren’t true, and therefore (you say) don’t even know whether I have a body, much less pockets or ten dollars. Skeptic: Yes... Anti-skeptic: So it turns out that, by your own standards, I don’t know how to prove that I have ten dollars in my pocket, even if I’m not tied up! Skeptic: Erm... Anti-skeptic: So “I have ten dollars in my pocket” is not, after all, an example of something that I require proof to know. Skeptic: Rather, I’d say that you do require proof to know it, and that since you can’t prove it, you don’t know it. Anti-skeptic: But the whole question is whether knowing something requires being able to prove it! If I can’t prove that I have ten dollars by pulling a ten dollar bill out of my pocket, then I say: that just goes to show that I can know what I can’t prove. Nothing you’ve said so far suggests otherwise. Anyway, I deny that I can’t prove that there is an external world. Skeptic: Really? What’s your proof?

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Anti-skeptic: Well, do you agree that if there are thousand dollar bills, then there is an external world? Skeptic: Certainly. Thousand dollar bills, if they exist, are rectangles of paper produced by a printing press. So if a thousand dollar bill exists, so does paper and a printing press -- both of which would be external objects existing independently of my mind. Anti-skeptic: Right. Well, as it happens, I have a thousand dollar bill in my pocket. Skeptic: No you don’t. Anti-skeptic: [pulls a thousand dollar bill out of his pocket]

Skeptic: Holy cow! Anti-skeptic: Now do you believe me? Skeptic: Sure. I mean no! I could be a brain in a vat, maybe this is just a dream--- Anti-skeptic: But you did take the appearance of the $1,000 bill as proof of my claim to have such a bill, and even if you hadn’t said as much, everything in your behavior would have confirmed that you accepted what I did as proof. Skeptic: Like what? Anti-skeptic: Like, if your life depended on immediately coming up with a thousand dollars in cash, you would ask me to lend you my thousand dollar bill. Skeptic: But I deny that I could ever know that my life depended on anything -- as far as I know, there is no external world to contain any threats to my life. Anti-skeptic: You say that, but you don’t really believe it. You are suffering from a peculiar form of self-deception that arises in philosophical discussions about skepticism. You feel like you doubt that there is an external world, but you don’t really doubt it. You feel like you don’t believe you know that there is an external world, but you really do take yourself to know it. Of

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course, none of this proves that there is an external world, or that you know that there is. It just proves that you believe that you know that there is. That is, it proves that you are not, despite your name in this dialogue, a Skeptic. Ex-skeptic: I guess you’re right about that. But still, that skeptical argument sure is a puzzler. Anti-skeptic: It sure is. For my part, I’m rather partial to a phenomenalistic solution to the puzzle. III. Phenomenalism John Stuart Mill: Hey Tom. Thomas Nagel: Hey John, what’s up? JSM: Nothing much. Just working on this theory I’ve come up with. TN: Oh yeah, what’s it about? JSM: It’s about the nature of reality and our knowledge of it. I call it “phenomenalism.” TN: Cool. Tell me more. JSM: Well, I was thinking about the skeptical argument, and it occurred to me that its first premise is wrong. TN: That’s the one that says that there could be a universe that consisted of nothing but your own thoughts and experiences? JSM: Yeah, that’s it. TN: I must say, it sounds pretty plausible to me. JSM: Well, it seems to me that there couldn’t be such a universe. TN: Why not? JSM: Because there has to be something that causes my thoughts and experiences -- something distinct from my thoughts and experiences themselves. It just doesn’t make sense to think that all the events of my mental life just occur for no reason: there must be something outside of my mind that causes me to have these experiences. If no such external causes existed, I wouldn’t have experiences at all. So premise (1) of the skeptical argument is false: it couldn’t have been the case that only my own mental states existed: in order for these mental states to exist, there must also exist some external causes of those mental states.

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TN: That’s an interesting thought, but I think I see a problem with it. JSM: Oh, what? TN: Even if it’s true that your mental states have external causes, what reason could you possibly have to think that these causes were what we normally take them to be? I mean, the common sense view is that treeish experiences are caused by trees. But a skeptic will say that common sense might very well be mistaken. Maybe what causes my treeish experiences is an Evil Demon, or a super-computer sending signals to an envatted brain or to a body immersed in a pod in the Matrix. JSM: What’s the Matrix? TN: You know, the Matrix -- Neo, the red pill and the blue pill? “Whoa.” It was a popular movie. JSM: Oh, sorry. Dad and Bentham don’t let me get out much. TN: Anyway, even if I grant you that your conscious experiences must have causes external to your mind, why should I grant that these causes take the form of trees, rocks, fish, and other commonsense things? JSM: Well, by “tree,” I just mean whatever causes treeish experiences in me. Likewise for “stone,” “river,” “planet,” “mosquito,” “car,” “storm,” “tax refund,” etc. Each of these terms is just defined as that which causes the sorts of experiences that we associate with it. To say that there are trees is to say no more, and no less, than that there are things that produce treeish experiences in us. So from the fact that our treeish experiences have causes, it automatically follows that there are trees. Whether the causes of my treeish experiences are in some sense “similar” to the experiences is irrelevant. If the causes of my treeish experiences are acts of an Evil Demon or signals from a computer, that just means that trees are fundamentally constituted by such acts or signals. TN: But you seem to be forgetting that not all causes of treeish experiences are trees. When I dream of a tree, the cause of my experience is a random event in my slumbering brain. And when I mistake a realistic sculpture of a tree for a tree, the cause of my experience is a mass of concrete and wax.

JSM: Fair enough. But I still say that “there are trees” just means that something (or some things) cause(s) an overall pattern of experiences of the sort I actually have. For there to be trees is simply for there to be something with the power to cause patterns of experiences of the sort I associate with real trees, rather than fake, dreamt, or hallucinated trees. Patterns of experiences that include visual images of axes bouncing off rock-hard “trunks,” or “leaves” melting in the sun, or a forest suddenly replaced by my bedroom, or “bark” falling away to reveal hidden dryads, do not count. By “trees” I do not mean the causes of these kinds of experiences, but the causes of “normal” tree experiences. TN: But couldn’t it turn out that what normally causes treeish experiences in us is fake trees? JSM: No, I don’t think so.

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TN: Hmmm. I feel we may be reaching an impasse here. Anyway, I have another problem with your suggestion. Why should we believe that our experiences have any causes at all? If we don’t know that they have causes, then we don’t know that there are trees, even by your reckoning. JSM: They must have causes, or if not causes per se, and least explanations. Something has to explain why I have the experiences I do. TN: Why? Maybe all your experiences just occur randomly. JSM: Well, maybe that is a logical possibility. I mean, I can’t see any outright contradiction in the claim that all my experience happens randomly, without anything to explain it. But the chances of all these experiences happening in this orderly way at random are so small as to be negligible. I mean, it would be far more likely for a troupe of monkeys banging on typewriters to produce a copy of Shakespeare’s Hamlet. TN: OK. Suppose I grant that. But you’re not just claiming that your experiences have causes. You are claiming that they have causes external to your own mind. What is the basis of that claim? For all you know, everything that happens in your mind is caused by some other event that happens in your mind. In that case, it’s true that everything that happens in your mind has an explanation -- it’s just that it’s explained by something else that happens in your mind. So your mind could still be the whole universe. JSM: But how could that be? If each of my mental states is caused by another one of my mental states, I’d have to have an infinite number of mental states! Each mental state would be caused by a prior mental state, which would in turn be caused by a mental state prior to it, etc., etc., ad infinitum. TN: Well, how do you know you haven’t had an infinite chain of past experiences? All you have to go on here is your memories, which could exist just as they do even if there were huge swaths of your past that they didn’t cover. At least, that’s what a skeptic would say. JSM: But it’s not just that each of my thoughts and experiences individually must have some explanation. There must also be an explanation for the fact that I have the whole series of thoughts and experiences I do. And whatever explains this cannot belong to this series itself. TN: That reminds me of something I once read by David Hume. Oh, look, I have quote right here -- it’s from his Dialogues Concerning Natural Religion. He writes: “If I were to show you the particular causes of each individual in a collection of twenty particles of matter, I should think it very unreasonable, should you afterwards ask me what was the cause of the whole twenty. This is sufficiently explained in explaining the cause of the parts.” JSM: Well, Hume is right about the twenty particles, but a collection of twenty particles is not analogous to a supposedly infinite chain of experiences. TN: Why not? JSM: Let me explain with a different analogy. Suppose we discover a spherical object drifting in outer space. We ask: why does this object exist? It turns out the the object consists of a series of nested spherical shells, like an onion. Each shell is half as thick as the next shell in, and there are infinitely many shells.

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TN: OK, I understand the example so far. JSM: Good. Now imagine that someone offers the following “explanation” of the sphere’s existence. The outermost shell, A, was caused by the next shell in, B. B, in turn, was caused by the next shell in, C. And so on, ad infinitum. It took 1 second for B to generate A, ½ second for C to generate B, ¼ second for the next shell in to generate C, etc. So the whole generative process took 2 seconds. TN: A funny sort of explanation. JSM: In fact, it’s no explanation at all! We still don’t know why this whole process of concentric generation occurred. The existence of the sphere has not been explained, despite the fact that we have explained why each part of the sphere exists. Similarly, even if I could explain each of my experiences by reference to some other, prior experience that caused it, it would remain to be explained why I have any experiences at all -- why this whole chain of experiences exists in the first place. And whatever explains that is what I call “Reality.” TN: Well, I must say that this theory of yours has more to it than meets the eye. JSM: I’m glad you think so. If you want to hear more about it, you might take a look at a paper by David Chalmers. Pelczar has assigned it for the last week of the term. TN: Will do. Bye now. JSM: Bye.

M.W.P.