Kant was among the first[i] to break decisively with the eudaimonistic tradition of classical ethics by declaring that the moral principle is entirely distinct and divergent from the principle of happiness (G 4:393, KpV 5:21-27).[ii] I am going to argue that what is at issue in Kant’s rejection of eudaimonism is not fundamentally any question of ethical value or the priority among values. On the contrary, on these matters Kant shares the views which led classical ethical theory from Socrates onward to embrace eudaimonism. Instead, where Kant breaks with classical ethics is in the conception of human nature. Kant’s conception of human nature so altered the application of moral principles that it forced a change in the way happiness was conceived, leading to a reversal of what had earlier been thought about the relation of the principle morality to the pursuit of happiness.