David Chalmers' famous zombie argument

Is it true that consciousness is constituted by (or: supervenes on) matter? No, it is not. In his book The Conscious Mind. In Search of a Fundamental Theory David Chalmers provides an interesting argument against the claim that matter constitutes consciousness. I shall briefly paraphrase his argument. According to Hume's dictum conceivability entails metaphysical possibility. That is to say, if we can conceive of some state of affairs X, then, plausibly, X is metaphysically possible. Now, surely, unconscious zombies that are materially and behaviorally identical to conscious human beings are conceivable. For, to conceive of such zombies we don't need to do anything more than to conceive of some finite collection of externally observable structures, actions and responses. An appeal to internal conscious states is thus not necessary. But then Hume's aforementioned dictum entails that it is metaphysically possible for there to be unconscious zombies that are materially and behaviorally identical to conscious human beings. And from this it follows that consciousness is not constituted by matter. For, if it would, then such zombies would in fact not be metaphysically possible at all. So, indeed, materialism fails.