The Virtues of Functionalism

As I see it, functionalism about the mind (the view that all mental states can be defined purely in terms of a relation between sensory inputs and behavioral outputs), has three primary benefits. That is, there are three primary reasons a contemporary philosopher, with a physicalist bent and a strong respect of science, may want to accept it. They are the following:

(1) Functionalism, unlike the identity-theory of mind, preserves multiple realizability. What this means is that different neural structures could, in principle, realize one and the same type of mental state. This is important because it seems, for example, implausible that lower animals which seem to be conscious, but lack our particular neural structure, could not realize a mental state like pain. But if functionalism is true, all that's needed to preserve the same type of mental state is to have the same type of sensory inputs and behavioral outputs.

(2) Functionalism is compatible with a strong supervenience physicalism. The reason for this is that, if mental states are defined purely in terms of a relation between sensory inputs and behavioral outputs, then mental states will always and only supervene on those types of facts, which are (obviously) purely physical. So, functionalism is well-grounded in the physical world, and indeed dependent upon it.

(3) Functionalism makes sense from an evolutionary standpoint. Unlike dualism, forms of epiphenomenalism, and even simple property-dualism, functionalism has a plausible evolutionary story. If mental states really do function as a means of sensory inputs eventually having specific behavioral outputs, then its obvious why and how they could have evolved: Evolution selects for behavior, and if some type of mental state provided for the necessary means to achieve that survival-beneficient behavior, it would be selected for and, well, here we are today.