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[Music] Hi, I'm David Charas. I'm professor of philosophy at New York University. I work especially in the philosophy of mind and consciousness. And today I'm going to talk about zombies. Philosophical zombies, that is.
Philosophical zombies arise when philosophers are thinking about consciousness and its relationship to the physical world. Phenomenal consciousness, as philosophers call it, is the subjective experience of the mind and the world. Conscious experience from the first person point of view. We say a being is conscious in this sense if there is something it is like to be that being from the first person perspective. So humans are conscious. At least I'm conscious. There's something it's like to be me. And I hope there's something it's like to be you. Most people think that dogs are conscious. They have subjective experience. There's something it's like to be them. Most people think that rocks are not conscious. There's nothing it's like to be a rock. A rock has no first person perspective involving feelings and perceptions and thoughts.
Many philosophers think that consciousness poses the biggest challenge to materialism, the view that the world is wholly physical or material. The big question is, how can objective physical processes like neurons firing in the brain explain the subjective experience of consciousness? The sensation of the color red, the feeling of pain, the experience of thoughts running through one's mind.
There are a number of arguments against materialism based on consciousness. There's the knowledge argument. There's the explanatory argument, which you'll touch on elsewhere, but I'm going to focus on what philosophers call the conceivability argument, which focuses on philosophical zombies.
What is a philosophical zombie? A philosophical zombie is a being that's physically identical to a conscious human being, but that isn't conscious. There's nothing it's like to be a zombie. For a zombie, everything is dark inside, kind of like that rock. Um, there's no subjective experience for a zombie. But from the outside, they look just like a normal human being. So, my zombie twin might be behaving just like me, even saying all these things, but would have no consciousness on the inside.
Now, zombies, as philosophers think about them, are quite distinct from the zombies you find in Hollywood movies and distinct from the zombies you find in various ancient traditions, such as the voodoo tradition in Haiti. The zombies you find in Hollywood movies tend to be dead, but reanimated, brought back to life. They behave very unlike ordinary human beings. Maybe they even have some kind of subjective experience. Maybe it tastes like something to them when they eat their victims. The zombies of the Haitian voodoo tradition are traditionally understood as beings that lack free will. They're poisoned, um, and therefore someone can take them over as servants. They have no free will of their own. So all these zombies lack something. Hollywood zombies lack life. The voodoo zombies lack free will. But philosophical zombies lack consciousness. That's what that's what's missing. They're outwardly like normal humans, but they lack consciousness.
Few people think that zombies actually exist. Proponents of zombies usually don't say that, you know, there are zombies actually around us. But many philosophers argue that zombies are at least conceivable. We can coherently imagine that other people are not conscious. When you see me talking, it's a coherent possibility for you that I'm having no subjective experience. I'm just as processes in my brain brain. I'm talking about them and so on. Even if you imagine all of the brain processes of an ordinary human being, it seems to be no contradiction in the idea that they're not conscious. If that's right, then zombies are at least conceivable.
Philosophical zombies can be used for many different philosophical purposes. One use for them is to raise the philosophical problem of other minds, which we can put as saying, how do we know that the people around us aren't zombies? How do we know that they're conscious at all? It also raises questions about the function of consciousness in the physical world. Why didn't evolution produce zombies? If zombies lacking consciousness can do all the things that we do, why did evolution produce consciousness at all? That's still very much an open question.
But the use I'm interested in today is using philosophical zombies to argue against a materialist view of the world. And here the basic idea is that, yeah, there could be a purely physical world, but that would be a world of zombies with no consciousness at all. Philosophers have turned this into an argument, sometimes called the conceivability argument or sometimes just called the zombie argument. The argument goes like this. First, zombies are conceivable. Second, if zombies are conceivable, they're metaphysically possible. Third, if zombies are metaphysically possible, then materialism is false. The conclusion of the argument, putting all these premises together, is that materialism is false.
Now, each of these premises can be disputed. As always in philosophy, um, arguments aren't proofs of their conclusion because, uh, there's room to dispute the premises. And materialists have responded to this argument in various different ways. But first, the basic intuitive idea behind this argument is the following. If zombies are conceivable, then let's think about God creating the world metaphorically as a kind of metaphor. Then if zombies are conceivable, it seems that God could have created a zombie world, one that's physically like ours, but that lacks consciousness. If so, then to make sure that there's consciousness in the world, to make sure we're conscious, God needs to do more work beyond creating the physical world. God needs to put consciousness into the world, too. And from that, it seems to follow that consciousness is something non-physical.
But there are a number of objections to this argument, and the materialists have put forth. The zombie argument is extremely controversial. The first kind of objection says zombies are not even conceivable. If we really try to imagine them in detail, we'll fail. You just haven't tried well enough to imagine all the details. Dualists at this point reply that even when we imagine all the details, consciousness may be absent. What's going on here is not just a lack of detail. It's a principled gap between, you know, objective physical processes and subjective experience.
A second objection is that conceivability doesn't entail metaphysical possibility. Just because you can conceive that something's the case doesn't mean the world really could have been that way. You know, philosophers like examples like this. It's conceivable that water isn't H2O, but it's not possible. Once we really understand chemistry, we can understand why H2O just is water and there's no difference between them. By analogy, they'll say it's conceivable that consciousness isn't physical. It's conceivable there be some non-physical consciousness, but once we understand neuroscience, we'll understand that consciousness just is a brain process. So that it's not possible that consciousness isn't physical. Consciousness is a process in the brain. This is a very complex argument. But some dualists have replied that at least there are certain kinds of conceivability that do entail possibility, like idealized conceivability with full information and full reasoning. And they'll argue that zombies are actually ideally conceivable in that sense. Of course, that's controversial.
Third, some materialists have said that metaphysical possibility tells us nothing about the actual world. Perhaps there's a possible world where consciousness is non-physical, but our world isn't like that. So, mere possibility is irrelevant for materialism. In reply, the dualist says that to be a materialist, you have to say that physical processes necessitate consciousness. There is a necessary connection between brain processes and consciousness, not just a correlation. If zombies are even metaphysically possible, then brain processes don't necessitate consciousness. They merely correlate with consciousness. And that's not materialism anymore. That's itself a form of dualism.
Philosophical zombies also raise issues in the philosophical analysis of artificial intelligence. A central question in the philosophy of artificial intelligence or AI is, could AI systems running on computers be conscious? For example, in the TV series Star Trek: The Next Generation, we see Commander Data, an android, and the question is raised in the series, is he conscious? Could this silicon machine be conscious? And it seems there are two hypotheses. Hypothesis one is that Data is conscious. He has a rich conscious mind full of the experience of people. He's seeing thoughts running through his head. "I am conscious, therefore I am." Feelings of pain and so on. That's the hypothesis that he's conscious. On an alternative hypothesis, Data is a zombie. He behaves in many sophisticated ways. He speaks, maybe he reasons, but he has no subjective experience. Where subjective experience is concerned, he's just a blank. These are two hypotheses about artificial intelligence systems. They'll be conscious or they'll be zombies. So, hypothesis one, there's something it's like to be Data. Hypothesis two, Data functions like a human, but he's not conscious. There's nothing it's like to be him.
Some materialists may themselves say that Data is a zombie. Some materialists think consciousness is biological. They may say Data lacks biology, therefore he's not conscious. He's a kind of zombie. Other materialists think that consciousness is a computational process of the kind you might find in a computer. Then they may say that Data is conscious and he's not a zombie. Dualists will say it's conceivable and possible that Data is a zombie, just as it's conceivable and possible that a biological system with a brain is a zombie. But property dualism is compatible with AI systems being conscious. We can conceive of zombies with brains like ours that are not conscious, but as a matter of fact, we're not zombies. Likewise, we could conceive of AI systems with silicon processes that lack consciousness, but it doesn't follow from that that in practice they'll be conscious. That's itself an open question for the science and the philosophy of consciousness.
The question of whether AI systems are conscious or zombies, whether they can be conscious, that's central to the future of artificial intelligence. If AI systems are zombies, then it seems that basically they're just tools for us to use with no subjective experience, no rights of their own. But if AI systems are conscious, then it seems they might eventually be people, be thinking systems with conscious perception, feeling, thought, desires, reasoning. And indeed, it seems that if they have all that, then they may well be people with rights of their own. That if so, if AI systems are not zombies, that will have very strong conclusions for the future of AI, for the future of technology, and perhaps even the future of humanity.
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