- Thomas Bontly's discussion of naturalism raises another set of issues related to the realization of mental states by physical states. Naturalism is both a constraint upon, and a goal of, much of current philosophy of mind, but Bontly's discussion elegantly reminds us that few if any of us are able to say what naturalism2 is. For some, naturalism is simply a methodological thesis (a position reflected in "Sober (Elliott) - The Principle of Conservatism in Cognitive Ethology") — to be natural is to subject to investigation by a battery of methods recognizable as scientific. Bontly's claim is that naturalism, if it is a substantive thesis at all, is a thesis about the way in which mental states are realized in the world described by physics. After all, a central tenet of naturalism seems to be that the respective ontologies of the various branches of science comprise a unity.
- One common way to cash out the presumed unity implicit in naturalism is to appeal to causal closure. Everything that is natural, it is commonly supposed, comprises a domain which is causally closed and complete. To make a case that putative entities of a certain kind constitute part of the natural world one simply has to show their role in the causal structure of the world. The way to demonstrate that intentional states are natural is to show how they are realized in the world by states susceptible of strictly physical description. The way to demonstrate the autonomy of the intentional sciences seems to require that intentional states play some irreducible causal role in the closed causal structure of the physical world. But the rub is that the causal closure of the physical world is incompatible with the causal efficacy of mental states. If we insist that the mental must be realized in the physical we risk either the causal exclusion of the mental or causal over-determination in the sense that every event with a mental cause also has a sufficient physical cause.
- Bontly is dubious of this sort exclusion argument. It threatens to introduce either exclusion or over-determination for every cause which supervenes3 on some physical state or other. Supervenient properties are not in general excluded by their subvening physical realizers. So the fact that mental states supervene4 on physical states should not exclude them from being independently causally efficacious. Nor, in general, is it the case that demonstrating the causal efficacy of a property of a given kind requires demonstrating the manner of its physical realization. There is little reason to suppose that the overly stringent naturalistic standards that have been applied in the realm of intentional psychology are any more appropriate there than in any other field of the natural sciences.
Footnote 1: Taken from "Walsh (Denis) - Naturalism, Evolution and Mind: Editor's Introduction".
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