Michael Smith attempts to solve the moral problem by arguing that our moral beliefs constitute a rational constraint on our desires. In particular, Smith defends the ‘practicality requirement’, which says that rational agents who believe that an action is right must have some desire to perform that action. We clarify and examine Smith’s argument. We argue that, for the argument to be sound, it must make two crucial assumptions about the rational agent in question: that facts about her desires are (...) transparent to her, and that she believes that she is rational. We conclude that if Smith has solved the moral problem then he has done so only for a restricted class of subjects—those who satisfy these two assumptions. (shrink)