> but this does not preclude imagining a p-zombie, any more than a knowledge of anatomy and aerodynamics precludes imagining a dragon.

It kind of does. The argument goes: if you can imagine a p-zombie, then in your mind it's possible that consciousness is not tied to physical qualities. Therefore, physicalism would necessarily be false.

It took me awhile to accept this, but the solution is simple: p-zombies can't exist because I can't imagine them. And this is because consciousness must serve a functional purpose, and so p-zombies would be distinguishable from humans.