Philosophically inclined psychologists and psychologically inclined philosophers often hold that the substantive discoveries of psychology can provide an empirical foundation for epistemology. In this paper it is argued that the ambition to found epistemology empirically faces certain unnoticed difficulties. Empirical theories concerned with knowledge?gaining abilities have been historically associated with specific epistemological views such that the epistemology gives preferential support to the substantive theory, while the theory empirically supports the epistemology. Theories attribute to the subject just those epistemic abilities which (...) associated epistemologies attribute to the scientist. The concept of epistemological significance is introduced as the significance a psychological theory can have for modifying the epistemological suppositions with which the theory was originally associated. Substantive psychological theories are strongly constrained by the epistemologies used in their development; the endorsement an epistemology receives from its associated theory should carry no weight. The alliance between psychology and epistemology is not progressive to the development of either field. Alternative sources of progress in epistemology and psychology are suggested. (shrink)