 Explanations in terms of reasons have several features that distinguish them from explanations in terms of causes. Reasons purport to justify the actions they explain, and indeed so called “external reasons” (Williams 1981) only justify action, without purporting to explain it. Reasons can be evaluated, and they are responsive to criticism. Reasons, unlike causes, must be intelligible to those for whom they are reasons. On grounds such as these, many philosophers have questioned whether explanations of human action can be causal explanations (von Wright 1971, Winch 1958). Yet merely giving a reason — even an extremely good reason — fails to explain an agent’s action, if the reason was not in fact “effective.” Someone might, for example, start attending church regularly and give as his reason a concern with salvation. But others might suspect that this agent is deceiving himself and that the minister’s attractive daughter is in fact responsible for his renewed interest in religion. Donald Davidson (1963) argued that what distinguishes the reasons that explain an action from the reasons that fail to explain it is that the former are also causes of the action. Although the account of rationality within economics differs in some ways from the  folk psychology  people tacitly invoke in everyday explanations of actions, many of the same questions carry over (Rosenberg 1976, ch. 5; 1980, Hausman 2012).