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.)

So I do, of course, reject much that is central not only to the psychology of Descartes and Kant, but to their epistemology as well. No doubt, the best available theories of today will look primitive in comparison with what we are in a position to understand hundreds of years from now.

One of the goals of scientific theorising is to develop concepts which are adequate to the phenomena under study. In my view, things should work the same way in epistemology. We want to know what knowledge actually amounts to, not what our folk concept of knowledge is, since, just as with our pretheoretical concept of acidity, it might contain all sorts of misunderstandings and leave out all manner of important things.

Here, as in so many other cases, however, it turns out that a very commonsensical idea looks far less attractive when one examines some of the experimental work which is not available to us from the armchair.

By putting the first-person point of view in a naturalistic perspective, I believe that we may genuinely come to understand it for the first time.

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?

What we need to do, however, is figure out what our best available theories of the mind suggest about epistemological issues, while we recognise that we may need to change our views on these questions as new evidence comes in.