Hume has a special place in justifications of claims made for rational choice theory to offer a unified language and explanatory framework for the social sciences. He is invoked in support of the assumptions characterising the instrumental rationality of agents and the constancy of their motivations across different institutional settings. This paper explores the problems with the expansionary aims of rational choice theory through criticism of these appeals to Hume. First, Hume does not assume constancy. Moreover, Hume’s sensitivity to the (...) relationships between institutional setting and individual motivation owes something to the relative transparency of the plural language of vices and virtues that he employs. Second, rational choice theory’s minimal modification of Hume’s account of the relation of reason and the passions through the introduction of constraints of consistency on preferences is unstable. (shrink)