There are many topics within philosophical discussion. One can even distinguish them for their relevance in different areas of research. Some are relevant for political theory and political science, some for sociology, others for literary and film theory, and some for psychology. It is the last of these that I am interested in. I want to know how humans cognize their environment. Typically, this is understood within the broad study area of Philosophy of Mind. The question is wide. It may even involve some biology, depending on the standpoint. My present worry, however, does not concern the relevance of philosophical discussions within theory of mind. Rather, I am worried about the philosophy-psychology relation itself. How, if at all, are we supposed to cash out the psychological data in philosophical terms?
One way to do this, the one I can imagine (at least), is to assume that all philosophical claims depend upon implicit or explicit assumptions about human psychology. Thus, I tend to think that ANY philosophical theory of, say, perception or perceptual content, MUST fit in the evidence from psychological studies. I know of, at least, three ways of attacking this claim.
One possible attack comes from the hardcore narrow-minded philosopher. According to her, whether or not philosophy meets the psychological data is, at best, a matter of coincidence. Thus if, say, a Cartesian theory of knowledge comes out to be psychologically non-sense, still there might be some room for it within the altar of philosophy. I think this view is either too arrogant, or too humble. In both cases, it turns out to be useless.
Another possible attack comes from the hardcore separatist. According to her, philosophy and psychology split. One is concerned with psychological facts, the latter with logical facts. Thus, when we wonder whether Descartes theory is correct, we wonder whether it is logically consistent. And it might be logically consistent even if psychologically impossible. One reply to this, the one I have to offer, is to demand that the subject matter be determined. It might very well be (though I doubt it) that logical and psychological questions split at some point. Nevertheless, if both philosophers and psychologists are wondering about the same subject matter (i.e., how humans cognize their environment), it better be that their answers are consistent with each other.
Finally, a third attack comes from fans of philosophical prior. According to her, philosophy is always prior to any other inquiry. As such, it must first be answered before any other inquiry can get started. Psychological evidence presupposes a solution to the central philosophical issues. Thus, it is useless, for philosophical purposes, to appeal to psychological data. It turns out to be some sort of a vicious circle. I believe the history of science has greatly retorted to this objection. If philosophical solutions were really needed, we would have no scientific development for the past millennia – assuming, as it seems to be, that no agreed theory has come up for philosophical problems about cognition since, at least, Aristotle. It seems that psychology is pretty well off without solving philosophical problems.
The way I see this, logically consistent theories of knowledge are plentiful. The number of good, acceptable ones is pretty large. In any case, it is definitely larger than the number of acceptable psychological accounts of human cognition. After all, logical laws bound logical inquiry, whereas psychological inquiry is bound by the data. It seems to me to be natural to expect that the psychological accounts narrow down the inquiry by eliminating logically possible, yet unsuitable, accounts of cognition. And this can be done by demanding from our philosophy that it fits-in the psychological data.