Zombies may imitate a smile but do they do not experience happiness.

Do you believe in zombies? No, not those zombies. Philosophical zombies. They look just like people. In philosophical terms, they are physically identical to us. They have brains, blood flows around their bodies, they laugh at appropriate times, and if you pinch them, they are likely to say ‘Ow!’ Functionally, they are indistinguishable. However, they lack consciousness.

There’s a key similarity between both kinds of zombie: each is said to lack consciousness. Moreover, most of us hope neither exists outside of fiction. While the place of regular zombies is in stories (usually horror), the place of philosophical zombies is in thought experiments (usually in philosophy of mind).

Now here’s why it matters: how do you prove that somebody—even somebody you’ve known for your entire life (e.g., a friend or someone with whom you’re in love)—is not a philosophical zombie?

Sure, you can sense the signals of their body (e.g., the sounds it makes, the light it reflects, the odours it gives off). But on what basis is your experience of them indicative of theirs?

Maybe you deduce mental life in them by analogy to yours. However, this takes a Cartesian leap of faith; for what is your philosophical argument? (Wittgenstein speaks of experience as a ‘beetle in the box’ which can only be inferred in someone else and not articulated, given private language’s inaccessibility.)

Maybe you can send them to a neurophysiologist to find ‘correlates of consciousness’; but this won’t prove experience alone.

In short: in your experience, yours is the only consciousness you are directly aware of.

And here’s the point: if we conceive of philosophical zombies as a logical possibility and believe that humans are distinguishable from them, it follows that we should refute physicalism as a means of explaining consciousness (David Chalmers). Why?

The very conceivability of zombies undermines explanations of consciousness in physicalism’s terms. (Remember, zombies share all our physical features.) We need something else to tell us apart from zombies since physicalism fails to show we are different.

The power of this argument, of course, rests on how conceivable we think zombies are. If you think zombies are conceivable, you have a problem in having no way of verifying others’ consciousness. If you don’t, you’re burying your head in the non-philosophical sand until you come up with a convincing argument.

But what does this argument say about the power of philosophy?

Maybe it’s best not to think about zombies at all.

ED: Any zombies out there?
SHAUN: Don't say that!
ED: What?
SHAUN: That.
ED: What?
SHAUN: That. The Z word. Don't say it.
ED: Why not?
SHAUN: Because it's ridiculous!
ED: [sighs and rolls his eyes] All right … Are there any out there, though? Shaun of the Dead (2004)