In Mental Acts, Geach, criticizing some doctrines about concept and judgment, offers his own views about them. I shall examine his accounts of concept-formation, exercises of concepts, judgment as mental acts, and the analogy-theories of psychological concepts. All of these are intimately interconnected. Geach begins by affiming the existence of mental acts, reports of which are categorical, not hypotetical or semi-hypothetical statements. His main reason for rejecting Ryle’s view that psychological statements are hypothetical or semi-hypothetical statements about overt behaviour is that “actus est prior otentia”.