Bealer has a number of reasons for thinking that a naturalistic epistemology is self-undermining. Let me focus on one of these. (I've tried to take on all of them in the first chapter of Knowledge and Its Place in Nature.)

What I hankered for was an account of knowledge which would do far more than get our intuitions about cases right; I wanted a kind of account which would somehow be explanatory.

The fact that we have been able to develop a successful science, which issues in ever more accurate predictions and broader explanations, is the real ground for confidence that we are in a position to gain knowledge of the world around us. At the same time, one might ask how it is that the cognitive equipment we have came about, and here, no doubt, our evolutionary origins are relevant.

There is a worry that many have expressed that, on the naturalistic way of approaching philosophical questions, philosophy will somehow be co-opted by science. I'm not much worried about this.

If we want to make sense of the possibility of successful inductive inference, and if we want to explain the possibility of laws of nature, we will need to appeal to something like natural kinds. This is, to be sure, a metaphysical commitment, but it is a metaphysical commitment that is implicit in science, as I see it.

Rather, although belief may be adequate for explaining the behavior of individual animals - an animal which believes that p will behave no differently from an animal which knows that p - talk of knowledge is necessary once one begins to look at explaining the cognitive capacities of a species.

I was often asked how one could even make sense of this. Isn't the category of knowledge something that we project upon the world, rather than something that we discover in it?