The advice that results from this information will not always be what a priori ideals would dictate. Objections to naturalism 1. At best, its claims about knowledge, whether in actuality true or false, are unjustified, because any flaws in our methods will prevent us from uncovering our errors. At worst, we may simply conclude that our current reasoning practices are paradigms of proper belief formation when in fact they may be deeply flawed. In order to justify one set of claims, some other set must be taken for granted, at least temporarily.
Epistemology is logically prior to science.
We must first figure out what makes beliefs justified, and in an a priori manner. Until we do so, we have no way of judging if our current beliefs are a useful source of information about the beliefs we ought to have to have knowledge. Prescriptions about knowledge must take into account human cognitive abilities and limitations. Science will tell us how far human beings tend to be from the ideal and what might be required for getting them closer to the ideal. The a posteriori methods of science tell us not only what human beings are capable of, but the correct rules of epistemic justification as well.