TED日本語 - ジョン・サール: 意識 – 私達人間に共通するもの

I'm going to talk about consciousness. Why consciousness? Well, it's a curiously neglected subject, both in our scientific and our philosophical culture.

Now why is that curious? Well, it is the most important aspect of our lives for a very simple, logical reason, namely, it's a necessary condition on anything being important in our lives that we're conscious. You care about science, philosophy, music, art, whatever -- it's no good if you're a zombie or in a coma, right? So consciousness is number one. The second reason is that when people do get interested in it, as I think they should, they tend to say the most appalling things. And then, even when they're not saying appalling things and they're really trying to do serious research, well, it's been slow. Progress has been slow.

When I first got interested in this, I thought, well, it's a straightforward problem in biology. Let's get these brain stabbers to get busy and figure out how it works in the brain. So I went over to UCSF and I talked to all the heavy-duty neurobiologists there, and they showed some impatience, as scientists often do when you ask them embarrassing questions. But the thing that struck me is,one guy said in exasperation, a very famous neurobiologist, he said, "Look, in my discipline it's okay to be interested in consciousness, but get tenure first. Get tenure first."

Now I've been working on this for a long time. I think now you might actually get tenure by working on consciousness. If so, that's a real step forward.

Okay, now why then is this curious reluctance and curious hostility to consciousness? Well, I think it's a combination of two features of our intellectual culture that like to think they're opposing each other but in fact they share a common set of assumptions. One feature is the tradition of religious dualism: Consciousness is not a part of the physical world. It's a part of the spiritual world. It belongs to the soul, and the soul is not a part of the physical world. That's the tradition of God, the soul and immortality. There's another tradition that thinks it's opposed to this but accepts the worst assumption. That tradition thinks that we are heavy-duty scientific materialists: Consciousness is not a part of the physical world. Either it doesn't exist at all, or it's something else, a computer program or some damn fool thing, but in any case it's not part of science. And I used to get in an argument that really gave me a stomachache. Here's how it went. Science is objective, consciousness is subjective, therefore there can not be a science of consciousness.

Okay, so these twin traditions are paralyzing us. It's very hard to get out of these twin traditions. And I have only one real message in this lecture, and that is, consciousness is a biological phenomenon like photosynthesis, digestion, mitosis -- you know all the biological phenomena -- and once you accept that, most, though not all, of the hard problems about consciousness simply evaporate. And I'm going to go through some of them.

Okay, now I promised you to tell you some of the outrageous things said about consciousness. One: Consciousness does not exist. It's an illusion, like sunsets. Science has shown sunsets and rainbows are illusions. So consciousness is an illusion. Two: Well, maybe it exists, but it's really something else. It's a computer program running in the brain. Three: No, the only thing that exists is really behavior. It's embarrassing how influential behaviorism was, but I'll get back to that. And four: Maybe consciousness exists, but it can't make any difference to the world. How could spirituality move anything? Now, whenever somebody tells me that, I think, you want to see spirituality move something? Watch. I decide consciously to raise my arm, and the damn thing goes up. (Laughter)

Furthermore, notice this: We do not say, "Well, it's a bit like the weather in Geneva. Some days it goes up and some days it doesn't go up." No. It goes up whenever I damn well want it to.

Okay. I'm going to tell you how that's possible. Now, I haven't yet given you a definition. You can't do this if you don't give a definition. People always say consciousness is very hard to define. I think it's rather easy to define if you're not trying to give a scientific definition. We're not ready for a scientific definition, but here's a common-sense definition. Consciousness consists of all those states of feeling or sentience or awareness. It begins in the morning when you wake up from a dreamless sleep, and it goes on all day until you fall asleep or die or otherwise become unconscious. Dreams are a form of consciousness on this definition.

Now, that's the common-sense definition. That's our target. If you're not talking about that, you're not talking about consciousness.

But they think, "Well, if that's it, that's an awful problem. How can such a thing exist as part of the real world?"

And this, if you've ever had a philosophy course, this is known as the famous mind-body problem. I think that has a simple solution too. I'm going to give it to you. And here it is: All of our conscious states, without exception, are caused by lower-level neurobiological processes in the brain, and they are realized in the brain as higher-level or system features. It's about as mysterious as the liquidity of water. Right? The liquidity is not an extra juice squirted out by the H2O molecules. It's a condition that the system is in. And just as the jar full of water can go from liquid to solid depending on the behavior of the molecules, so your brain can go from a state of being conscious to a state of being unconscious, depending on the behavior of the molecules. The famous mind-body problem is that simple.

All right? But now we get into some harder questions. Let's specify the exact features of consciousness, so that we can then answer those four objections that I made to it.

Well, the first feature is, it's real and irreducible. You can't get rid of it. You see, the distinction between reality and illusion is the distinction between how things consciously seem to us and how they really are. It consciously seems like there's -- I like the French "arc-en-ciel" - it seems like there's an arch in the sky, or it seems like the sun is setting over the mountains. It consciously seems to us, but that's not really happening. But for that distinction between how things consciously seem and how they really are, you can't make that distinction for the very existence of consciousness, because where the very existence of consciousness is concerned, if it consciously seems to you that you are conscious, you are conscious. I mean, if a bunch of experts come to me and say, "We are heavy-duty neurobiologists and we've done a study of you, Searle, and we're convinced you are not conscious, you are a very cleverly constructed robot," I don't think, "Well, maybe these guys are right, you know?" I don't think that for a moment, because, I mean, Descartes may have made a lot of mistakes, but he was right about this. You can not doubt the existence of your own consciousness. Okay, that's the first feature of consciousness. It's real and irreducible. You can not get rid of it by showing that it's an illusion in a way that you can with other standard illusions.

Okay, the second feature is this one that has been such a source of trouble to us, and that is, all of our conscious states have this qualitative character to them. There's something that it feels like to drink beer which is not what it feels like to do your income tax or listen to music, and this qualitative feel automatically generates a third feature, namely, conscious states are by definition subjective in the sense that they only exist as experienced by some human or animal subject, some self that experiences them. Maybe we'll be able to build a conscious machine. Since we don't know how our brains do it, we're not in a position, so far, to build a conscious machine.

Okay. Another feature of consciousness is that it comes in unified conscious fields. So I don't just have the sight of the people in front of me and the sound of my voice and the weight of my shoes against the floor, but they occur to me as part of one single great conscious field that stretches forward and backward. That is the key to understanding the enormous power of consciousness. And we have not been able to do that in a robot. The disappointment of robotics derives from the fact that we don't know how to make a conscious robot, so we don't have a machine that can do this kind of thing.

Okay, the next feature of consciousness, after this marvelous unified conscious field, is that it functions causally in our behavior. I gave you a scientific demonstration by raising my hand, but how is that possible? How can it be that this thought in my brain can move material objects? Well, I'll tell you the answer. I mean, we don't know the detailed answer, but we know the basic part of the answer, and that is, there is a sequence of neuron firings, and they terminate where the acetylcholine is secreted at the axon end-plates of the motor neurons. Sorry to use philosophical terminology here, but when it's secreted at the axon end-plates of the motor neurons, a whole lot of wonderful things happen in the ion channels and the damned arm goes up. Now, think of what I told you. One and the same event, my conscious decision to raise my arm has a level of description where it has all of these touchy-feely spiritual qualities. It's a thought in my brain, but at the same time, it's busy secreting acetylcholine and doing all sorts of other things as it makes its way from the motor cortex down through the nerve fibers in the arm. Now, what that tells us is that our traditional vocabularies for discussing these issues are totally obsolete. One and the same event has a level of description where it's neurobiological, and another level of description where it's mental, and that's a single event, and that's how nature works. That's how it's possible for consciousness to function causally.

Okay, now with that in mind, with going through these various features of consciousness, let's go back and answer some of those early objections.

Well, the first one I said was, consciousness doesn't exist, it's an illusion. Well, I've already answered that. I don't think we need to worry about that. But the second one had an incredible influence, and may still be around, and that is, "Well, if consciousness exists, it's really something else. It's really a digital computer program running in your brain and that's what we need to do to create consciousness is get the right program. Yeah, forget about the hardware. Any hardware will do provided it's rich enough and stable enough to carry the program."

Now, we know that that's wrong. I mean, anybody who's thought about computers at all can see that that's wrong, because computation is defined as symbol manipulation, usually thought of as zeros as ones, but any symbols will do. You get an algorithm that you can program in a binary code, and that's the defining trait of the computer program. But we know that that's purely syntactical. That's symbolic. We know that actual human consciousness has something more than that. It's got a content in addition to the syntax. It's got a semantics.

Now that argument, I made that argument 30 -- oh my God, I don't want to think about it - more than 30 years ago, but there's a deeper argument implicit in what I've told you, and I want to tell you that argument briefly, and that is, consciousness creates an observer-independent reality. It creates a reality of money, property, government, marriage, CERN conferences, cocktail parties and summer vacations, and all of those are creations of consciousness. Their existence is observer-relative. It's only relative to conscious agents that a piece of paper is money or that a bunch of buildings is a university.

Now, ask yourself about computation. Is that absolute, like force and mass and gravitational attraction? Or is it observer-relative? Well, some computations are intrinsic. I add two plus two to get four. That's going on no matter what anybody thinks. But when I haul out my pocket calculator and do the calculation, the only intrinsic phenomenon is the electronic circuit and its behavior. That's the only absolute phenomenon. All the rest is interpreted by us. Computation only exists relative to consciousness. Either a conscious agent is carrying out the computation, or he's got a piece of machinery that admits of a computational interpretation. Now that doesn't mean computation is arbitrary. I spent a lot of money on this hardware. But we have this persistent confusion between objectivity and subjectivity as features of reality and objectivity and subjectivity as features of claims. And the bottom line of this part of my talk is this: You can have a completely objective science, a science where you make objectively true claims, about a domain whose existence is subjective, whose existence is in the human brain consisting of subjective states of sentience or feeling or awareness. So the objection that you can't have an objective science of consciousness because it's subjective and science is objective, that's a pun. That's a bad pun on objectivity and subjectivity. You can make objective claims about a domain that is subjective in its mode of existence, and indeed that's what neurologists do. I mean, you have patients that actually suffer pains, and you try to get an objective science of that.

Okay, I promised to refute all these guys, and I don't have an awful lot of time left, but let me refute a couple more of them. I said that behaviorism ought to be one of the great embarrassments of our intellectual culture, because it's refuted the moment you think about it. Your mental states are identical with your behavior? Well, think about the distinction between feeling a pain and engaging in pain behavior. I won't demonstrate pain behavior, but I can tell you I'm not having any pains right now. So it's an obvious mistake. Why did they make the mistake? The mistake was- and you can go back and read the literature on this, you can see this over and over - they think if you accept the irreducible existence of consciousness, you're giving up on science. You're giving up on 300 years of human progress and human hope and all the rest of it. And the message I want to leave you with is, consciousness has to become accepted as a genuine biological phenomenon, as much subject to scientific analysis as any other phenomenon in biology, or, for that matter, the rest of science.

Thank you very much.

(Applause)