Batman Jr. said:
Why does materialism have to lead only to p-zombies? How can you show that physical processes cannot account for consciousness?
How can materialism imply anything more than p-zombies? The physical world only deals with structure and function. Consciousness has to play a fruitful role in some scientific theory describing the world. But it is clear that if the world is physically closed that it can be described entirely from a 3rd person perspective (ie objective perspective).
Here is what I have said on this subject before:
Let me address the reason why I think materialism is unintelligible. What we need to do is take a look at materialism to see if it is internally consistant. Now the particular question I would like to address is why should we suppose that other peoples bodies are "inhabited" by conscious minds (or why phenomenal consciousness is associated with brains). Your argument no doubt will be that materialism stipulates this to be so; it is an axiomatic premise of materialism. But this makes your definition of materialism an arbitrary one. A metaphysic which glosses over awkward facts. Allow me to explain.
It seems to me that materialism should stipulate that the physical exhausts reality. That once we have completely described the Universe in physical terms then we have said all that can be said about the Universe or reality.
But what is the physical? It seems to me that it should be everything, that, at least in principle, can be observed by anyone with appropriate faculties and suitable instruments. In other words all that is objective exists, or to put it another way, all that is discernable from the third person perspective exists. This will also include things which can only be indirectly seen (although strictly speaking I reject the direct/indirect dichotomy). This then includes such entities as electrons, because although they can only be "indirectly" seen they nevertheless play fruitful roles in our theories describing the world ie we need to hypothesise electrons in order to explain certain aspects of reality.
Now there is something peculiar about conscious experience which marks it off from all other existents. It is simply this. It cannot be observed or detected by anyone with appropriate faculties and/or suitable instruments! Thus according to my prior definition of the physical it is not a physical existent. Thus I may have toothache to take an arbitrary example. But you cannot observe that toothache, all you can obseve is the effects of the toothache, the grimace of pain for example. Conscious experiences in other words are irreducibly private.
Now you will no doubt say that by observing the grimace, or at least by observing the neurons fire, then you are observing the toothache since materialism holds that the toothache and its neural correlates are one and the same thing, or at least aspects of the same thing. But an objective examination of this toothache will necessarily leave out the subjective irreducibly sensation of pain. The actually sensation of pain does not figure into the physical facts about the pain according to our prior definition of the physical. Nor can we infer the sensation of pain since, unlike an electron, the (phenomenological) pain does not play a part in any description of our behaviour. The pain per se cannot play a part because pain per se is not part of the objective publically accessible realm. Only the neural correlates of the pain can play any fruitful role in our theories.
In short then either a materialist has to concede his metaphysic is internally inconsistent, or he must arbitrarily include phenomenological consciousness within his world picture. But if he opts for the latter then the whole prima facie plausibility of his world view crumbles away. No longer can he say that for something to exist it must be in principle be directly observable or play a fruitful role in some theory about the world, because this then necessarily precludes phenomenological consciousness. He
has to expand the notion of the physical to even include things that cannot be directly or even indirectly detected, even in principle!
This is what materialism entails and is just one of many reasons why we should reject this metaphysic.