Lomasky offers accounts of public choice and of political philosophy, in which these disciplines have complementary theories of motivation, and suggests that each discipline can learn something from the other. This note argues that these two theories of motivation share a common weakness: an a priori, non-empirical mode of analysis. Political philosophy models human beings as rational moral agents; public choice theory treats individuals as rationally self-interested. Neither theory is concerned with the psychology of actual human motivation. This common feature facilitates the transfer of ideas between the two disciplines, but it limits the usefulness of both. There is more to political motivation than can be captured by theories of reason.