Reduce Them All: A General Theory of Psychophysical Reduction

I propose and defend a novel version of reductive functionalism about mental phenomena. This theory makes three key contributions. First, I argue that reduction should be understood as a question of ‘nomic equivalence’ between tokens of the reducing and base type, as well as the inheritance of causal powers by the former from the latter. This definition sets aside issues about, e.g., the priority of physics over other special sciences. Second, I suggest a solution to what I call the generality problem. This problem is that other such theories offer only ‘local’ or species-specific reductions, such that human pain reduces to physical type H, dog pain to physical type D, and so on, but fail to explain what all pain states have in common. I argue that the Homeostatic Property Cluster theory of natural kinds offers a framework in which both more finely grained, type-reducible mental categories as well as broader, species-general mental categories count as natural kinds. Finally, I add a tool to the reductionist’s kit for responding to the multiple realizability objection. I propose a novel functionalism in which mental states are the core, rather than the total realizers of functional roles. This allows the reductionist to handle a distinct class of multiple realizers: those where the core component is embedded differently in distinct realizing mechanisms. For instance, digital video displays are multiply realizable in (at least) LCD and CRT form, but such displays share a core component that is ‘doing the work’ of displaying videos by illuminating various pixels. By identifying the functional (and in this case artifactual) kind with the core component of pixel illuminators, we can reduce it to the sufficiently similar physical bases of those illuminators