It is philosophical zombies that I’m most interested in here, since I’m a philosopher and they raise very interesting issues. The sort I’m most concerned with are zombies that are physically and behaviorally identical to a conscious human, but lack any conscious experience. As in this case-study of my own zombie twin, for example.
Most people doubt that zombies could exist in the actual world. (In philosophical terms, they are naturally impossible.) But many people think that they are at least logically possible – i.e. that the idea of zombie is internally consistent, and that there is at least a “possible world” where zombies exist. This logical possibility is sometimes used to draw strong conclusions about consciousness (e.g. in my book The Conscious Mind, and elsewhere).
- It can be used as a way of illustrating the “hard problem” of consciousness: why do physical processes give rise to conscious experience? This question might equally be phrased as “why aren’t we zombies?”. If any account of physical processes would apply equally well to a zombie world , it is hard to see how such an account can explain the existence of consciousness in our world.
- It can be used to raise questions about the function of consciousness: why did evolution bother to produce us if zombies would have survived and reproduced just as well? (As e.g. Flanagan and Polger have argued.)
- And it can even be used to argue against materialism. If there is a possible world which is just like this one except that it contains zombies, then that seems to imply that the existence of consciousness is a further, nonphysical fact about our world. To put it metaphorically, even after determining the physical facts about our world, God had to “do more work” to ensure that we weren’t zombies.
The general point is that the logical possibility of zombies is one way of illustrating that there is no logical entailment from physical facts to facts about consciousness, whereas there is such an entailment in most other domains. Of course even the logical possibility of zombies is controversial to some (e.g. Dennett ), as conceivability intuitions are notoriously elusive; and some scientists have been known to wonder whether anything important really follows from what is merely conceivable. I think that most arguments that use zombies can actually be rephrased in a zombie-free way, so that these arguments can be set aside if one prefers; but zombies at least provide a vivid and provocative illustration.