Chalmers on the Apriority of Modal Knowledge

Abstract

David Chalmers's book on consciousness (1996) has a number of admirable qualities it is bold, imaginative, articulate, well informed, and in a number of places, enormously illuminating. It is also true, however, that several passages in the book have significant flaws. I discuss two of these passages in the present note. A main point of the book is to argue for property dualism that is, for the claim that the intrinsic properties of conscious experiences are distinct from all physical and functional properties. Chalmers's argument for this claim can be summarized as follows: 'In order for the facts of consciousness to be reductively explainable in terms of physical and/or functional facts, it must be the case that it is logically impossible for there to be a world w such that (a) w is just like the actual world with respect to all physical and functional facts, but (b) w fails to contain all of the facts of consciousness that obtain in the actual world. Now it is epistemologically appropriate to test for logical possibility and logical impossibility by a priori methods, and in particular, it is appropriate to test for whether it is logically possible for there to be a world that meets conditions (a) and (b) by seeing whether one can conceive of such a world. When we apply this test, we find that it has a positive outcome. Thus, for example, we find that we can conceive of a world in which the physical and functional facts are the same as they are in the actual world but in which consciousness is altogether absent a world in which there are physical/functional twins of all beings who possess consciousness in the actual world but in which those twins are zombies. It turns out, then, that it is logically possible for there to be a world that meets conditions (a) and (b), and by the same token, it turns out that the facts of consciousness are not reducible to physical and/ or functional facts. We can conclude from this that the properties in virtue of which states count as conscious experiences are distinct from physical and functional properties.' It is clear that this argument for property dualism depends heavily on the claim that we have a priori access to logical possibility. In the present paper I examine two passages in which Chalmers appears to offer justifications for this view. The passages I focus on are not the only ones in the book that offer such justifications, and in fact Chalmers informs me that the passages in question are not the ones that he regards as making the strongest case for his view. Despite this disavowal by Chalmers, however, it seems to me to be important to subject the passages in question to critical scrutiny.