 Although Aristotle is deeply indebted to Plato’s moral philosophy, particularly Plato’s central insight that moral thinking must be integrated with our emotions and appetites, and that the preparation for such unity of character should begin with childhood education, the systematic character of Aristotle’s discussion of these themes was a remarkable innovation. No one had written ethical treatises before Aristotle. Plato’s Republic, for example, does not treat ethics as a distinct subject matter; nor does it offer a systematic examination of the nature of happiness, virtue, voluntariness, pleasure, or friendship. To be sure, we can find in Plato’s works important discussions of these phenomena, but they are not brought together and unified as they are in Aristotle’s ethical writings.