Sunday, September 03, 2006

Physicalism: Reduction and Unity

The article "There is no question of physicalism" by Crane and Mellor is pretty good, at least for the first half. They argue that there is no non-vacuous version of physicalism that is true. One thing they say that is in accord with what Dupre said is that physicalism depends on a unity of science thesis that doesn't look like it will work out. I was initially surprised to see that, but after giving it some thought, it makes sense. The grand pyramid of unified science has physics at the bottom and everything else building up on top of it. Each successive layer is reducible to the one below it, ultimately reducible to physics. So the story goes. Mellor and Crane point out that there is no reason to believe this microreduction thesis. There are phenomena that physics studies (Mach's law, special relativity) that do not look reducible or require macroscopic objects. In any case, they argue, it isn't explained what kind of physics we are supposed to be reducing to. The choices are present physics and future physics. If the prior, then we a priori rule out entitites of future physics if that ontology differs from the present's. If the future, how can we say what that ontology will be? That's a convincing dilemma.

The most interesting point of the article was when they pressed the question of why microphysical reduction gets this sort of ontological say. The answer seems to come from Occam's razor: if you can reduce one domain of entities to another, then you should take the smaller domain. But, just because everything has these micro-constituents, does that give us reason to think that the macro-things don't exist? Their answer is no. Their reason is that the microreduction thesis doesn't by itself say anything about the existence of macroscopic objects. In order to get that, you have to bring in auxialiary premises, one of which is a massive application of Occam's razor. But, once you deploy Occam's razor, what force does Crane and Mellor's point have? It looks undermined to me.

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