The Norton Introduction to Philosophy, ed. Rosen, Byrne, Cohen and Shiffrin Skepticism about the Internal World1 Alex Byrne 1. Introduction You know much about your own mental or psychological life. Perhaps there is some of it that you can only know after years of therapy, but it's easy to know, for example, that you have a headache, that you want water, that you believe that it's raining, and that you see a cat. Epistemologists (philosophers who study knowledge) have generally concentrated on knowledge of another sort, namely knowledge about your environment that you gain through perception-knowledge that there is water in the glass, that it's raining, that the cat is on the mat, and so on. The chief reason for this focus on "external world" knowledge is the threat of skepticism. There is, it is often said, an apparently compelling argument for "skepticism about the external world", the alarming claim that we do not know anything about our environment. According to the skeptic about the external world, we may know many things about our mental lives, but as to whether there is beer in the fridge, or whether the fridge exists at all, we are irremediably ignorant. Because many philosophers think the skeptic's case is hard to answer, they conclude that there is something deeply puzzling about our knowledge of our environment. I shall argue that this is all back to front. The real puzzle is not how we know about our environment, but how we know about our own minds. The argument for skepticism about the external world has an obvious weak point, but the argument for skepticism about our own minds-skepticism about the "internal world"-is much more difficult to dismiss. Let us start by discussing a standard argument for skepticism about the external world. Once we have seen how this is not very convincing, we will be in a position to mount a parallel and potentially more powerful argument for skepticism about the internal world. 2. Skepticism about the external world In his First Meditation, Descartes considers the possibility that he is not, as he seems to be, sitting by a fire and holding a piece of paper, but instead is in bed enjoying an especially vivid dream. He "sees plainly", he says, "that there are never any sure signs by means of which being 1 This essay is dedicated to the memory of Fred Dretske. 2 awake can be distinguished from being asleep". Accordingly, he (provisionally) concludes that he does not know that he is awake and sitting by the fire. What goes for Descartes goes for the rest of us, of course. If he is right, I do not know that I am sitting in a chair, balancing a laptop on my knees. And-it is easy to think-he is right. After all, if I were vividly dreaming that I am sitting in a chair things would seem just the same as they do when I really am sitting in a chair. 2.1. The external world skeptical argument examined Descartes is not very explicit about why there are no "sure signs" that indicate that he is awake and sitting by the fire, rather than in bed fast asleep. For some assistance, let us turn to a passage from Barry Stroud's classic book The Significance of Philosophical Scepticism, in which Stroud draws some lessons from the First Meditation: If we are in the predicament Descartes finds himself in at the end of his First Meditation we cannot tell by means of the senses whether we are dreaming or not; all the sensory experiences we are having are compatible with our merely dreaming...Our knowledge is in that way confined to our sensory experiences...There seems to be no way of going beyond them to know that the world around us really is this way rather than that. (Stroud 1984: 31, my italics) To see the significance of the italicized phrases, imagine a detective investigating a murder. Mr. Boddy has been found stabbed in the library with a chef's knife, and Colonel Mustard and Professor Plum are the two suspects. Both men wanted Boddy dead, and both lack alibis for the night of the crime. A witness says he saw a tall man with a mustache enter the library, clutching a large knife. And that's it-the witness cannot be more helpful, there are no fingerprints or incriminating blood stains, nothing. The detective's problem is that both Mustard and Plum are tall and mustached. She might sum up her predicament as follows: "The witness's testimony and my other evidence are compatible with the hypothesis that Mustard is the murderer, and the rival hypothesis that Plum is the murderer. There seems to be no way of going beyond this evidence to know that one hypothesis is correct; my evidence, in other words, does not favor one hypothesis over the other. My knowledge is therefore confined to my evidence: I know that the murderer is tall and mustached, and used a chef's knife, but that is all." 3 So the quotation from Stroud suggests the following argument for skepticism about the external world. In general-the argument begins-our evidence for claims or hypotheses about the external world consists in facts about our sensory experiences. For example, your evidence for the hypothesis that you are sitting in a chair is that you seem to see the arms of the chair, seem to feel the pressure of the chair against your back, and so on. This evidence is compatible with other hypotheses, for instance the hypothesis that you are lying in bed vividly dreaming that you are sitting in a chair. And there seems to be no way of going beyond this evidence to know that one hypothesis is correct. Your evidence, in other words, does not favor the sitting hypothesis over the dreaming hypothesis, and so you do not know that the sitting hypothesis is true. It will be useful to set out the argument with numbered premises and a conclusion: P1. If you know that the sitting hypothesis is true, you know this solely on the basis of your evidence about your sensory experiences. P2. This evidence does not favor the sitting hypothesis over the dreaming hypothesis, and so does not allow you to know that the sitting hypothesis is true. Hence: C. You do not know that the sitting hypothesis is true; that is, you do not know that you are sitting in a chair. Obviously this argument generalizes from you to others, and from claims about sitting in a chair to other sorts of external world claims. If it is sound, then everyone is completely ignorant about their environment. Setting aside the issue of whether this is faithful to Descartes' intentions, it is certainly one of the standard arguments for skepticism about the external world. Since the argument is valid, the only way to avoid the conclusion is to deny one of the premises. And in fact, one premise looks highly suspicious on closer examination, namely P1.2 According to P1, if you know that you are sitting in a chair, that knowledge is based on your evidence about your sensory experiences. Now if someone knows a hypothesis H on the basis of her evidence E, this implies that she has concluded or inferred H from E, which in turn implies that she knew E. For example, if part of the detective's evidence is that no fingerprints were found at the scene, and she knows that the murderer wore gloves on that basis, then the 2 P2 might also be called into question: see Vogel, "Skepticism and Inference to the Best Explanation", chapter 8 of this anthology. 4 detective must have known that no fingerprints were found at the scene. If the scene was fingerprint-free, but for some reason the detective was ignorant of this piece of evidence, then she couldn't have used it as a basis on which to extend her knowledge. As we might put it, if the detective didn't know that no fingerprints were found, this piece of evidence was not part of her evidence.3 Now consider certain non-human animals, for instance dogs. They have sensory experiences (or so we may suppose) but there is not much reason to think that they know that they have sensory experiences. Knowledge of one's own mind requires a sophistication that dogs appear to lack. So if a dog knows that there is a rabbit behind a tree by using its eyes, it is not on the basis of evidence about its sensory experiences. And if evidence about sensory experiences is not needed for a dog to have environmental knowledge, it isn't needed for us to have environmental knowledge either. You could know that you are sitting in a chair without appealing to evidence about your sensory experiences, and presumably you do. Hence P1 is false. Not surprisingly, proponents of the argument will have replies to this objection, which we cannot examine here. But whether or not those replies succeed in rescuing P1, at the very least that premise should not strike us as initially plausible. Let us see if the parallel argument for internal world skepticism is any better. 3. Skepticism about the internal world4 Let us start with an example. Suppose you are facing a cat asleep on a mat, the light is good, your visual system is working perfectly, and so on. Then, by using your eyes, you can come to know that the cat is asleep on the mat (or so we think). What you know-that the cat is asleep on the mat-has nothing to do with you or your perceptual state. The cat would have been peacefully sleeping whether or not you had been around to notice that fact. Here is a second fact: that you see the cat. It is important to realize that this is a very different sort of fact than the first. This fact, unlike the first, is about you and your perceptual state. You know the first fact, that the cat is asleep on a mat, by using your eyes. How do you know the second fact, that you see the cat? That is not an easy question to answer. 3 For a difficult but rewarding discussion of evidence and its relation to knowledge, see Williamson 2000, chapter 9. 4 The classic presentation of internal world skepticism is in Dretske 2003, to which this section is much indebted. 5 But here is a clue. Suppose I ask you a question that is not about you, or your perceptual state: "Is a cat here?" You may answer by attending to the scene before your eyes: "Yes, there's a cat, asleep on the mat". Now suppose I ask you a question that is about you and your perceptual state: "Do you see a cat?" Is your way of answering that second question much different from the way you answered the first question? That is, don't you answer the second question also by looking? And looking is, apparently, all you need to do. If there's a cat right there, then you don't need any further information to answer confidently "Yes, I do see a cat". Since this point is absolutely crucial for what follows, we should dwell on it for a moment. Consider the following example. You are reading a newspaper story about last night's baseball game, in which the Red Sox came back in the bottom of the ninth to squeak out a victory over the Yankees. If the story is sufficiently interesting, the newspaper itself will fade into the background: you will be preoccupied with the message, not the medium. If I ask you "Were the bases loaded?" you will not be thinking about the newspaper font or the color of the page. But of course you can always shift your attention back from the message (the details of the game) to the medium (the newspaper). And indeed you must, if I ask you "Is the story printed in two columns?" or "Are you reading about the game in a newspaper?" In order to answer those questions, you have to turn your attention from the home run with the bases loaded to something quite different-paper and ink, held in your hands. In other words, you can't know that you are reading about the game just by attending to the game. The point is that the newspaper example is not a good model for how you know you see something. That is, if I ask you "Do you see a cat?" you do not have to attend to something that is analogous to the newspaper (perhaps a "sensory experience" or a "visual sensation"). When you read about the Red Sox, you don't just find facts about baseball, you also find the newspaper. But when you open your eyes, your seeing is in a way invisible. What you initially find is the world, not your seeing of the world.5 This suggests that in order to know that you see, you must somehow reach that conclusion from what you see. In other words, the evidence you use to find out that you see something is simply evidence about your visual environment, your environment as revealed to you by your sense of sight. That evidence includes facts about the cat (for example, that it is 5 For a much earlier version of the newspaper example, used to argue for (something close to) the opposite conclusion, see Broad 1927, p. 247. 6 black and furry), and facts about the cat's spatial relation to you (for example, that you are facing it). Now if someone claims to know hypothesis H on the basis of evidence E, one can challenge whether E really is good enough evidence for H by formulating a rival hypothesis H* that seems to be equally well supported by E. This happens all the time in science and everyday life, and was the basic idea of the external world skeptical argument, using the dreaming hypothesis as the alternative. But what hypothesis should we oppose to the seeing hypothesis, that you see a cat? For maximum vividness and generality we can make the alternative hypothesis as radical as can be. Consider the hypothesis that you do not have a mind at all. Outwardly you look and behave just as a minded person does, but really all is dark within: you do not see anything, think or believe or want or feel anything, and so on. So, in particular, you do not see the cat, despite its being (say) a few feet away in front of you in broad daylight. Call this the mindless hypothesis. Now your evidence about your visual environment-that the cat is black and furry, that you are facing it a few feet away in broad daylight, and other similar pieces of evidence-are compatible with both the seeing hypothesis and the rival mindless hypothesis. Offhand, it is not clear at all why this evidence favors the seeing hypothesis over the mindless hypothesis. Compare our earlier discussion of external world skepticism: if you agree that your evidence about your sensory experiences doesn't favor the sitting hypothesis over the dreaming hypothesis, then the parallel move for internal world skepticism should seem hard to resist. And if the evidence you have for the seeing hypothesis doesn't favor it over the mindless hypothesis, you don't know that the seeing hypothesis is true-you don't know that you see a cat. We can now set out our parallel argument with numbered premises and a conclusion: P1*. If you know that the seeing hypothesis is true, you know this solely on the basis of your evidence about your environment. P2*. This evidence does not favor the seeing hypothesis over the mindless hypothesis, and so does not allow you to know that the seeing hypothesis is true. Hence: C*. You do not know that the seeing hypothesis is true; that is, you do not know that you see a cat. 7 Notice that P1* seems more secure than P1. P1* was defended by reflection on how we actually go about discovering that we see things like cats, and is immune to the animals objection. If P1 is defensible at all, its defense is less straightforward. So far, so good, but how is the argument supposed to generalize to all mental states? It is fairly easy to see how the argument of the previous section generalizes-that's why it amounts to an argument for skepticism about the external world, rather than merely for skepticism about sitting. P1 seems no less plausible if we replace "the sitting hypothesis" by "the hypothesis that it's raining", or "the hypothesis that the earth is round", and so on. But now consider various other hypotheses about your mental life, say: The believing hypothesis: that you believe that the cat is asleep on the mat The liking hypothesis: that you like chocolate The feeling hypothesis: that you feel a twinge in your elbow Are the corresponding versions of P1* at all plausible? Perhaps surprisingly, a case can be made that they are. Take the believing hypothesis first. On the face of it, your way of answering the question "Do you believe that the cat is asleep on the mat?" (a question about your own mind) is not much different from your way of answering the very different question "Is the cat asleep on the mat?" In both cases you consider the cat, its state of wakefulness, and its relation to the mat, not your own mind. Once you have good evidence that the cat is asleep on the mat, then that is all you need to conclude that you believe that the cat is asleep on the mat.6 Now take the liking hypothesis. Why do you think you like chocolate? Isn't the answer something about the chocolate? You like chocolate because it tastes good. That is a fact about the chocolate, not about you. When you savor a piece of chocolate on your tongue, your sensory systems are detecting features of the chocolate, in particular its agreeable sweet taste. On the basis of this evidence about the chocolate you conclude that you like it. Finally, the feeling hypothesis. Surely here the corresponding version of P1* is obviously wrong! Well, that's right, if the "environment" is taken to be the environment external to your body, but there is no reason to adopt such a narrow construal. Your body is as much a part of your physical environment as the cat and the piece of chocolate. So consider the question "Do you feel a twinge in your elbow?" How do you go about answering it? By examining your own mind, wherever that is? No, by examining the elbow, of course. If there is the sort of disturbance 6 For an in-depth examination of this idea, see Moran 2001. 8 in the elbow that has the character of a twinge (rather than a dull ache, for example), then you will answer "Yes, I do feel a twinge in my elbow".7 Of course this is only a sketch of an argument for a fully general skepticism about the internal world. But let's assume that the details can be filled out. Does the argument face any obvious objections? 4. Two objections It is easy enough to feel the pull of the skeptic's claim that you can't rule out the hypothesis that you are dreaming. Many books and movies trade on this idea. It is considerably harder to see the force of skepticism about the internal world-the claim that you don't know that you have a mind might understandably strike you as too absurd to be worth discussing. Still, philosophy does not progress by dismissing arguments for absurd conclusions, but by carefully explaining where they go awry. Let us consider two objections. Seeing why neither works will help clarify the skeptical argument, and indicate that diagnosing its flaws is no easy matter. The first objection is that something must have gone badly wrong with the argument because the mindless hypothesis is incoherent. According to the mindless hypothesis, the objection runs, it seems to you that you have a mental life. It seems to you that you see, believe, desire, and so forth-even though you do not. But if it seems to you that such-and-such, then you are not mindless, because seemings are mental states. If it seems to you that you see a cat, then you might not be seeing a cat, but you certainly have a mind. This objection rests on a simple confusion. If you find it tempting, then you have failed to grasp just how outlandish the mindless hypothesis really is. According to the mindless hypothesis, it does not seem to you that you see a cat, for exactly the reason given in the objection. If the mindless hypothesis is right, you do not perceive, believe, or desire, and neither does it seem to you that you see, believe, or desire. The mindless hypothesis is not incoherent- at least, not in the way the first objection claims. So it is not misleadingly named: in the mindless scenario you are facing the cat with your eyes open, yet you seem to see nothing. 7 It is clear that the corresponding version of P2* is plausible for the believing hypothesis: how could the evidence that the cat is on the mat favor the believing hypothesis over the mindless hypothesis? The cat would be on the mat whether you believed it or not. Exercise: are the corresponding versions of P2* as plausible for the liking and feeling hypotheses? (See also Dretske 2003, pp. 4-6.) 9 The second objection also rests on a confusion, but this time it is more subtle. Return to the argument for external world skepticism, and the skeptic's claim that your knowledge is confined to evidence about your sensory experiences: there is no way of "going beyond" this evidence to know what the external world is like. If the argument for internal world skepticism is parallel, the internal world skeptic should presumably say something similar-namely, your knowledge is confined to evidence about your environment: there is no way of going beyond this evidence to know what the internal world is like. But wait-if the skeptic concedes that you know something then the mindless hypothesis is false! (You can't know something if you don't have a mind.) All that is quite correct, but it does not affect the argument. The skeptic is not arguing that the mindless hypothesis is true, but rather that you do not know that it is false. If it is false, then you do have a mind, and in particular you know various things about your environment. But, according to the skeptic, that is all you know-you can't "go beyond" this evidence to know what your mental life is like. The second objection does highlight one difference between external and internal world skepticism. The external world skeptic will allow that you have knowledge of some evidence (namely, evidence about your sensory experiences) if the dreaming hypothesis is true. In contrast, the internal world skeptic will not allow that you have any knowledge if the mindless hypothesis is true. That difference does not spoil the parallel between the two arguments, however. * * * * * The point of this article is not to convince you that you don't know anything about your own mind. Rather, the point is to highlight the problem of self-knowledge. We surely know a lot about our own minds-yet it is obscure how this is possible. Our knowledge of cats is quite well understood; our knowledge that we see cats, on the other hand, remains a mystery. 10 Bibliography Broad, C. D. 1927. Scientific Thought. London: Kegan Paul, Trench, Trubner & Co. Dretske, F. 2003. How do you know you are not a zombie? Privileged Access: Philosophical Accounts of Self-Knowledge, ed. B. Gertler. Aldershot: Ashgate. Moran, R. 2001. Authority and Estrangement. Princeton, NJ: Princeton University Press. Stroud, B. 1984. The Significance of Philosophical Scepticism. Oxford: Oxford University Press. Williamson, T. 2000. Knowledge and Its Limits. Oxford: Oxford University Press.