It is a well executed, though flawed, counter to Fodor’s arguments. First they give a nice rundown of the underdetermination issue I posted about here.
Then they discuss the “intensional fallacy”. They argue that the crux of F & P’s argument can be seen as trying to split up the causal efficacious trait and the selected-for trait. This means that F & P believe that there is no way to connect the evolutionary reason – the trait that increased an organism’s fitness – with our explanation of the trait that was selected-for. Block & Kitcher argue that it is trivial to match the two up because
selection-for is a causal notion, and, since causation is extensional, so is selection-for.
Insofar as we believe that our explanation of the selected-for trait is extensional, i.e. truth-preserving when switching between different names of the same thing, we can say that we do pick out the causally efficacious trait.
Unfortunately Block and Kitcher sacrificed our normal concept of explanation to make this counter-argument. They note that explanations are never normally extensional, but that we are making an exception in this case. This is ok to do because
we thinking beings can give (intensional) explanations in terms of [one trait] rather than the other properties. In giving the explanation, we (thinking beings) describe the property in our preferred way.
I do not understand what is going on here. Basically it looks as if “preferred way” is just a fancy way to say “own words”, but describing something in our own words doesn’t make it right. Nor is it a reason to change what should count as an explanation.
Unless Block and Kitcher are prepared to give further justification as to why we should disregard our normal understanding of explanation, it looks as if their solution to Fodor’s argument is ad hoc. They are using explanation* — which is a special kind of explanation that can be extensional — but they have not given a reason why explanation* should be preferred over of regular explanation (outside of causing Fodor trouble). Without this reason, the use of explanation* is ad hoc, and hence the argument fails because it turns on an ad hoc premise: the assumption that explanation* can be substituted for explanation.
However, I did say above that Block and Kitcher’s argument is well executed: My argument against using an ad hoc term-term* distinction is obscure compared to their argument and so, for the vast majority of people, it will appear that their argument is effective. Overall this is a good thing: less nonsense needs to surround evolution (though I’ll be a little sad to see it go: I’m #1 in a Google search for “fodor what darwin got wrong“).
[EDIT: I’ve put up a new analysis (24 March 2010) of Fodor’s argument here: Hypotheses Natura Non Fingo. It also includes a review of the responses of Block, Kitcher and Sober ]
For my take on what Fodor got wrong, see my post What Fodor Got Wrong, and the follow up Dismantling Fodor’s Argument (also linked above in reference to underdetermination). I’ll post something soon specifically addressing the intensionality issue: Fodor’s Intensional Criticism of Evolution.