Esa Diaz-Leon

A posteriori physicalism is the combination of two appealing views: physicalism (i.e. the view that all facts are either physical or entailed by the physical), and conceptual dualism (i.e. the view that phenomenal truths are not entailed a priori by physical truths). Recently, some philosophers such as Goff (2011), Levine (2007) and Nida-Rümelin (2007), among others, have suggested that a posteriori physicalism cannot explain how phenomenal concepts can reveal the nature of phenomenal properties. In this paper, I wish to defend a posteriori physicalism from this new and interesting challenge, by arguing that a posteriori physicalists have the resources to explain how phenomenal concepts can reveal at least something of what it would take for the corresponding phenomenal property to be instantiated.

In this paper I examine Chalmers and Jackson’s defence of the a priori entailment thesis, that is, the claim that microphysical truths a priori entail ordinary non-phenomenal truths such as ‘water covers 60% of the Earth surface’, which they use as a premise for an argument against the possibility of a reductive explanation of consciousness. Their argument relies on a certain view about the possession conditions of macroscopic concepts such as WATER, known as ascriptivism. In the paper I distinguish two versions of ascriptivism: reductive versus non-reductive ascriptivism. According to reductive ascriptivism, competent users of a concept have the ability to infer truths involving such concept from lower-level truths, whereas according to non-reductive ascriptivism, all that is required in order to be a competent user of a concept is to be able to infer truths involving that concept from other truths, which need not be lower-level truths. I argue, first, that the a priori entailment thesis is committed to reductive ascriptivism, and secondly, that reductive ascriptivism is problematic because it trivializes the notion of a priori knowledge. Therefore, I conclude that Chalmers and Jackson have not presented a convincing case for the claim that microphysical truths entail ordinary non-phenomenal truths a priori, especially when we understand this claim in the sense that is relevant for their argument against the possibility of a reductive explanation of consciousness.