Let's put to one side doubts that the presupposition that whether to rely or not on our cognitive faculties is a question of rational decision making. Not to rely on our faculties condemns us to a brief life of frustration. The naturalist will reject (2). Our faculties may be accidental, in the sense of contingent, but so is the Eiffel Tower. And they may not have arisen without accidental events such as random genetic mutations. But Bill ignores natural selection---the winnowing out of those mutations that diminish fitness relative to those that enhance it. We have reason to think that natural selection and genetic mutation have built effective and reliable legs, hearts, and digestive systems. Why not cognitive faculties too?1. It is rational to rely on our cognitive faculties to provide access to truths external to them.The limbs of the triad are individually plausible but collectvely inconsistent: they cannot all be true. From any two limbs one can validly argue to the negation of the remaining one. So, corresponding to our antilogism there are three valid syllogisms. One of them is a design argument that argues to the negation of (3) and the affirmative conclusion that behind the evolutionary process is intelligent, providential guidance. "And this all men call God."
2. It would not be rational to rely on our cognitive faculties if they had come about by an unguided process of natural selection operating upon random genetic mutations.
3. Our cognitive faculties did come about by an unguided process of natural selection operating upon random genetic mutations.
To resist this design argument, the naturalist must reject either (1) or (2). To reject (2) is to accept the rationality of believing both that our cognitive faculties arose by accident and that they produce reliable beliefs. It is to accept the rationality of something that, on the face of it, is irrational. To reject (1) is not very palatable either. But I suppose one could bite the bullet and say, "Look, we are not justified in relying on our cognitive faculties, we just rely on them and so far so good."
In a comment to the post Bill adds,
I am not confident about this topic, but I'll venture the following. I wonder whether reliable faculties are more conducive to reproductive fitness than unreliable ones. You will agree that reliability cannot be defined in terms of fitness. One cannot say that cognitive faculties are reliable just in case they lead to reproductive success. As I understand it, reliable faculties are those that can be trusted to deliver truth more often than not. It may well be that false beliefs are more adaptive than true ones.
Well, reliable legs, hearts, and digestive systems seem to be more conducive to reproductive fitness than unreliable ones. What reason has Bill to think that cognitive faculties fare any different?