special kind of skepticism

3 Other Minds There is one special kind of skepticism which continues to be a problem even if you assume that your mind is not the only thing there is -that the physical world you seem to see and feel around you, including your own body, really exists. That is skepticism about the nature or even existence of minds or experiences other than your own. How much do you really know about what goes on in anyone else’s mind? Clearly you observe only the bodies of other creatures, including people. You watch what they do, listen to what they say and to the other sounds they make, and see how they respond to their environment — what things attract them and what things repel them, what they eat, and so forth. You can also cut open other creatures and look -19- at their physical insides, and perhaps compare their anatomy with yours. But none of this will give you direct access to their experiences, thoughts, and feelings. The only experiences you can actually have are your own: if you believe anything about the mental lives of others, it is on the basis of observing their physical construction and behavior. To take a simple example, how do you know, when you and a friend are eating chocolate ice cream, whether it tastes the same to him as it tastes to you? You can try a taste of his ice cream, but if it tastes the same as yours, that only means it tastes the same to you: you haven’t experienced the way it tastes to him. There seems to be no way to compare the two flavor experiences directly. Well, you might say that since you’re both human beings, and you can both distinguish among flavors of ice cream — for example you can both tell the difference between chocolate and vanilla with your eyes closed — it’s likely that your flavor experiences are similar. But how do you know that? The only connection you’ve ever observed between a type of ice cream and a flavor is in your own case; so what reason do you have to think that similar correlations hold for other human beings? Why isn’t it just as consistent with all the evidence that chocolate tastes to him the way vanilla tastes to you, and vice versa? -20- The same question could be asked about other kinds of experience. How do you know that red things don’t look to your friend the way yellow things look to you? Of course if you ask him how a fire engine looks, he’ll say it looks red, like blood, and not yellow, like a dandelion; but that’s because he, like you, uses the word “red” for the color that blood and fire engines look to him, whatever it is. Maybe it’s what you call yellow, or what you call blue, or maybe it’s a color experience you’ve never had, and can’t even imagine. To deny this, you have to appeal to an assumption that flavor and color experiences are uniformly correlated with certain physical stimulations of the sense organs, whoever undergoes them. But the skeptic would say you have no evidence for that assumption, and because of the kind of assumption it is, you couldn’t have any evidence for it. All you can observe is the correlation in your own case. Faced with this argument, you might first concede that there is some uncertainty here. The correlation between stimulus and experience may not be exactly the same from one person to another: there may be slight shades of difference between two people’s color or flavor experience of the same type of ice cream. In fact, since people are physically different from one another, this wouldn’t be surprising. But, you might say, -21- the difference in experience can’t be too radical, or else we’d be able to tell. For instance, chocolate ice cream couldn’t taste to your friend the way a lemon tastes to you, otherwise his mouth would pucker up when he ate it. But notice that this claim assumes another correlation from one person to another: a correlation between inner experience and certain kinds of observable reaction. And the same question arises about that. You’ve observed the connection between puckering of the mouth and the taste you call sour only in your own case: how do you know it exists in other people? Maybe what makes your friend’s mouth pucker up is an experience like the one you get from eating oatmeal. If we go on pressing these kinds of questions relentlessly enough, we will move from a mild and harmless skepticism about whether chocolate ice cream tastes exactly the same to you and to your friend, to a much more radical skepticism about whether there is any similarity between your experiences and his. How do you know that when he puts something in his mouth he even has an experience of the kind that you would call a flavor? For all you know, it could be something you would call a sound — or maybe it’s unlike anything you’ve ever experienced, or could imagine. -22- If we continue on this path, it leads finally to the most radical skepticism of all about other minds. How do you even know that your friend is conscious? How do you know that there are any minds at all besides your own? The only example you’ve ever directly observed of a correlation between mind, behavior, anatomy, and physical circumstances is yourself. Even if other people and animals had no experiences whatever, no mental inner life of any kind, but were just elaborate biological machines, they would look just the same to you. So how do you know that’s not what they are? How do you know that the beings around you aren’t all mindless robots? You’ve never seen into their minds — you couldn’t — and their physical behavior could all be produced by purely physical causes. Maybe your relatives, your neighbors, your cat and your dog have no inner experiences whatever. If they don’t, there is no way you could ever find it out. You can’t even appeal to the evidence of their behavior, including what they say — because that assumes that in them outer behavior is connected with inner experience as it is in you; and that’s just what you don’t know. To consider the possibility that none of the people around you may be conscious produces an uncanny feeling. On the one hand it seems -23- conceivable, and no evidence you could possibly have can rule it out decisively. On the other hand it is something you can’t really believe is possible: your conviction that there are minds in those bodies, sight behind those eyes, hearing in those ears, etc., is instinctive. But if its power comes from instinct, is it really knowledge? Once you admit the possibility that the belief in other minds is mistaken, don’t you need something more reliable to justify holding on to it? There is another side to this question, which goes completely in the opposite direction. Ordinarily we believe that other human beings are conscious, and almost everyone believes that other mammals and birds are conscious too. But people differ over whether fish are conscious, or insects, worms, and jellyfish. They are still more doubtful about whether onecelled animals like amoebae and paramecia have conscious experiences, even though such creatures react conspicuously to stimuli of various kinds. Most people believe that plants aren’t conscious; and almost no one believes that rocks are conscious, or kleenex, or automobiles, or mountain lakes, or cigarettes. And to take another biological example, most of us would say, if we thought about it, that the individual cells of which our bodies are composed do not have any conscious experiences. -24- How do we know all these things? How do you know that when you cut a branch off a tree it doesn’t hurt the tree — only it can’t express its pain because it can’t move? (Or maybe it loves having its branches pruned.) How do you know that the muscle cells in your heart don’t feel pain or excitement when you run up a flight of stairs? How do you know that a kleenex doesn’t feel anything when you blow your nose into it? And what about computers? Suppose computers are developed to the point where they can be used to control robots that look on the outside like dogs, respond in complicated ways to the environment, and behave in many ways just like dogs, though they are just a mass of circuitry and silicon chips on the inside? Would we have any way of knowing whether such machines were conscious? These cases are different from one another, of course. If a thing is incapable of movement, it can’t give any behavioral evidence of feeling or perception. And if it isn’t a natural organism, it is radically different from us in internal constitution. But what grounds do we have for thinking that only things that behave like us to some degree and that have an observable physical structure roughly like ours are capable of having experiences of any kind? Perhaps trees feel things in a way totally different from us, but we -25- have no way of finding out about it, because we have no way of discovering the correlations between experience and observable manifestations or physical conditions in their case. We could discover such correlations only if we could observe both the experiences and the external manifestations together: but there is no way we can observe the experiences directly, except in our own case. And for the same reason there is no way we could observe the absence of any experiences, and consequently the absence of any such correlations, in any other case. You can’t tell that a tree has no experience, by looking inside it, any more than you can tell that a worm has experience, by looking inside it. So the question is: what can you really know about the conscious life in this world beyond the fact that you yourself have a conscious mind? Is it possible that there might be much less conscious life than you assume (none except yours), or much more (even in things you assume to be unconscious)?