About Face: Philosophical Naturalism, the Heuristic Identity Theory, and Recent Findings about Prosopagnosia*

1. Introduction It was a scientist, Ullin Place (1956), who first proposed the modern psycho-physical identity theory. Over subsequent decades, though, it has been philosophers of mind, who have seized on Place's proposal. Those philosophers directed most of their energies at finding fault with the identity theory. Armed with logic, ordinary language, an endless supply of intuitions about mind and mentality, thought experiments, and attention to the accomplishments of computers, philosophers-functionalists especially-assembled a list of arguments against the identity theory, most of which, however, fall into one or the other of two categories. The first group involves various apparent failures of the putative identities to satisfy Leibniz's law with regard to such matters as spatial properties, representational contents, consciousness, etc. Arguments about the identity theory's putative explanatory gaps and about its inability to surpass correlations are the most popular formulations of the first group's complaints. Broadly, the arguments hold either that the identity theory fails to explain how the brain can be said, sensibly, to possess various psychological properties or that any (conceivable) evidence for an identity of mind and brain can establish no more than correlations between them. By contrast, arguments of the second sort do not fret about the identity theory's alleged explanatory failures. Instead, the general strategy is to burden the identity theory with an embarrassment of riches. Multiple realizability arguments point to the prospect of so many possible physical arrangements realizing psychological states as to make the identity theory appear parochial in its focus on the human brain. William Bechtel and I have argued in two joint papers (Bechtel and McCauley 1999 and McCauley and Bechtel 2001) and independently (McCauley 2007 and Bechtel 2008) for a version of the identity theory, which we have dubbed Heuristic Identity Theory (HIT), that avoids both of these sorts of objections and squares better with actual scientific practice than earlier versions of the identity theory. We both see HIT as but one component of a larger naturalist program in philosophy that maintains that, all things being equal, philosophical projects in general are pursued more responsibly when they are pursued in the light of the activities, the methods, and the findings of the empirical sciences that philosophy has spawned both in centuries past and, in the cases of the psychological and cognitive sciences, fairly recently. (See, for example, Thagard 2010.) Exploring the identity theory within the framework of the sciences that …