Imagine a being that is exactly like you in every physical respect, down to the very atoms. This being walks and talks just like you and is behaviorally indistinguishable. Now imagine that this being doesn’t have any conscious sensations. You might prick this being on the arm and he/she might respond with a loud “ouch!” but they didn’t actually feel anything.
Do you think you have this being in your imagination? If so, according to David Chalmers, you have just proved physicalism- the idea that your mind, like everything else in the universe, is ultimately physical – false. How did you accomplish such a remarkable philosophical feat? Because you imagined a world that was physically identical to ours yet differed in one crucial respect: the beings on this zombie-world don’t have any conscious sensations, or raw-feeling. There are “additional facts” to the physical: experiences, sensations, etc. It is only necessary that this zombie-world is logically possible i.e. conceivable in order to prove physicalism false.
But before you get excited that your conceptual powers have defeated a long-standing philosophical position, I want to ask you some questions. Did you really imagine such a world? How would you prove to me that you, in fact, imagined such a world? Say you were David Chalmers, a philosopher, and wanted to show the world that you had in fact conceived a zombie-world and therefore shown physicalism to be wrong. How would you do this? You might engage in a variety of different behaviors such as flat out telling people verbally or writing long philosophical articles extolling in great detail how you in fact conceived of a zombie-world.
The key point here is that it is only through behavior that one could show that you have in fact conceived of a zombie-world. This is crucial because the zombie-world argument rests upon the idea that it isn’t physical actions that matter, it is the conscious sensations that go along with the behavior that matters, at least for the argument’s sake. The argument for additional facts only works if it is indeed possible to conceive of a world physically identical to ours yet differing in a very important way. But, how would you show to another person that you had indeed conceived of such an argument if not through physical behavior? Conceiving the conception of zombie-world is not quite the same as conceiving zombie-world itself.
Allow me to summarize: If the only possible way to show that you have actually conceived of the zombie-world is through actions, namely the writing of sophisticated philosophical arguments and verbal behavior, then doesn’t that undermine the purpose of such arguments in the first place?
Imagine you were having a conversation with a zombie-version of yourself. Do you think you would be convinced that he was indeed a zombie if his only argument was “But, I swear to Zeus that I have indeed conceived of zombie-world!You have to believe me!” Would you not be extremely skeptical of such arguments?