The Copernican revolution with which Kant transformed the question of whether knowledge is possible into the query as to how knowledge is possible, constitutes one stage in the development of epistemology from a speculative to an observational science — i.e., one that proceeds from the investigation of concrete, existent objects rather than from a small number of presupposed concepts. This path, leading from speculation to examination of the concrete objects of research — for epistemology, to the investigation of the various individual sciences — is long and arduous, and even now it has been traversed only a small part of the way. Although epistemological research has for a long time had some relation to mathematics and physics, and a more concrete exploration of biology and the humanities has recently been launched as well, we undoubtedly still stand at the very beginning of this enterprise. One major task for the epistemological inquiry into a specific discipline is bound up with tracing the course of development of that science — in particular, the radical shifts and readjustments in a science that promise to furnish the epistemologist with valuable information. Seen from this angle, psychology also currently deserves the special attention of epistemology.