Chalmers, Dennett, and the Zombies
The most striking thing about Chalmers' view of mind is how close to Dennett's it is in many respects. Contra Searle and other doubters, he argues for a strong form of AI in which any computer, what's more, every physical system that is an implementation of a suitable program (the one neurons in the brain implement, for example) will become conscious. The only point of disagreement with Dennett (except from some minor quibbles) is that for Dennett the conscoiusness is the information processing (IP), while for Chalmers consciousness is an extra fundamental feature of the world, correlated with the IP by contingent laws of nature akin to the fundamental laws of physics. This is the difference which Chalmers makes between "reductive" (bad) and "nonreductive" (good) functionalism.
But what is the cash value of the distinction? If it walks and quacks like a duck, it is a duck. If all and only all IP systems of a certain kind instantiate consciousness, the natural instinct of any scientist will be to apply Occam's Razor and say that consciousness just is the IP. It makes for a simpler worldview, makes science more unified (consciousness doesn't look like the kind of entity that appears in other fundamental physical laws), and dissolves all the paradoxes about epiphenomenalism and phenomenal judgements that trouble Chalmers.
Chalmers would protest that this is "not taking consciousness seriously". The connection between consciousness and IP is natural, not conceptual. One can imagine (concieve, in Chalmers' wording) beings with all the usual IP going on that a normal brain has but with no real, first-person point of view consciousness. This is the (in?)famous "zombie argument", which Chalmers coaches in a lot of modal terminology (possible worlds, primary and secondary intensions, and the like; Richard Chapell has a series of recent posts explaining these concepts). Dennett finds the argument ridiculous and preposterous, but his refutations are less than convincing, because he doesn’t touch what in my opinion are the deep sources of the disagreement between Chalmers and him.
Scientists would, in my opinion, not buy the zombie argument because they see little use for a distinction between a "conceptual" and a "nomological" necessitation of consciousness by physical facts. Is mass conceptually defined as a form of energy, or a distinct thing only nomologically correlated to it? It doesn't matter; as long as we agree in the pysical predictions made this is only a pragmatical question on how to axiomatize pysics. A 19th century pysicist would probably be able to "concieve" mass with no energy; does this prove anything? No; our concepts change and evolve with the growth of scientific knowledge; what is concievable now may become unconcievable later and vice-versa. Concepts are just tools for describing the world, and we can change them and reform them if we need to.
This picture of science, familiar since Quine, is pressupposed by Dennett, but implicitly rejected by Chalmers. When he talks of adding consciousness to the list of fundamental physical properties of the world, and adding the IP-consciousness correlation laws to the list of fundamental laws of nature, he overlooks that physics (despite common talk, even by physicists, even sometimes by me on behalf of convinience) does not provide a list of fundamental properties and a list of fundamental laws. It may provide a fundamental theory or a list of them (currently, they would be the Standard Model + Quantum Field Theory, and General Relativity, although we know that is not the end of the story as quantum gravity is left out) but not a list of fundamental entities the world is made of with a list of contingent laws of nature holding between them. What an entity such like the electromagnetic field is, is defined by what laws of nature it obeys and therefore by its relations with other entities. We can choose to make some features definitional and some others nomological, but that is mostly a matter of convinience and is subject to possible change in light of new knowledge. (This is, by the way, the reason I dislike the ubiquitous talk of “possible worlds” to frame philosophical questions. What counts as a possible world depends on the concepts used to describe them, which are subject to change with scientific progress.) Dennett himself makes the point when (addressing other thought experiments different from the zombie argument, but similar in style) he says:
Smiling demons, cow-sharks, Blockheads, and Swampmen are all, some philosophers think, logically possible, even if they are not nomologically possible, and these philosophers think this is important. I do not. Why should the truth-maker question cast its net this wide? Because, I gather, otherwise its answer doesn't tell us about the essence of the topic in question. But who believes in real essences of this sort nowadays? Not I.
I suspect Chalmers could agree with this with respect to all scientific concepts except consciousness. He would say that the concepts of phenomenal red or of pain cannot be subjected to the redefinitions possible for other scientific concepts. Our knowledge of them is by their intrinsic features (it is essential to pain, that it feels painful, while any functional properties of the state "being in pain" are not essential). This is the way Rorty characterizes the similar disagreement between Nagel and Dennett in his masterful essay "Holism, Intrinsicality, and the Ambition of Trascendence" (for Dennett and his critics). But this shows that all the zombie arguments are question-begging, because to carry any force they must assume that there is something very special about consciousness that distinguishes it from other subjects for science in the first place. A Dennettian would simply deny that the scientific description of consciousness requires concepts different in nature to those used in other areas.
To summarise, we can imagine a dialogue beetween Chalmers and Dennett to proceed like this:
C: We can concieve of zombies, therefore physics and IP do not conceptually entail consciousness, therefore consciousness is not identical to physical IP, even if it is universally correlated with it.
D: But if the correlation is indeed universal, then we better redefine our concept of consciousness to make it identical with physical IP and have a simpler scientific picture.
C: We cannot do that, because our present concept of consciousness captures intrinsic features of it, which cannot be done away with by redefinition.
D: This kind of intrinsic grasp on a concept does not exist anywhere else in science. To assume it does exist for phenomenal concepts is question-begging, because it makes from the start consciousness different from all other things.
Of course, this does not refute Chalmers' dualism; it merely shows that there is no non-circular agument for it. Dennett can still acknowledge the powerful tug of what he calls The Zombie Hunch as an "intuition", while going on to argue that reasons of scientific progress such as simplifying and clearing of "mysteries" our picture of the world speak in favour of not listening to that intuition.
If you want to know more about zombies and their use in philosophy, this resource page is the right place to go.