Certain philosophical arguments apparently show that the having of beliefs is tied conceptually to rationality. Such a view, however, seems at odds both with the possibility of irrational belief and with recent empirical discoveries in the psychology of reasoning. The aim of this paper is to move toward a reconciliation of these apparently conflicting perspectives by distinguishing between internalist and externalist conceptions of rationality. It is argued that elements of each are required for a satisfactory theory, one that allows for (...) the possibility of irrationality and makes sense of empirical findings without violating conditions on belief ascription. Normative theories, on this view, constrain the latter while remaining silent on the character of actual psychological mechanisms. (shrink)