The Nicomachean Ethics is, by many accounts, the first systematic treatise on ethics ever written. While Plato takes up a variety of ethical themes and topics throughout the dialogues, nowhere does he treat them as explicitly and deliberately as Aristotle. While Aristotle agrees with Plato that morality involves achieving harmony between reason and the emotions and appetites, and that good moral development begins in childhood, he largely rejects Plato’s metaphysics and replaces it with his own distinctively and thoroughly naturalistic method for engaging in ethical inquiry. A good human being, like all good things, fulfills its function or purpose well. What sets humans apart from plants and animals is their rational capacities; as such, the human function must consist in the proper development and exercise of these rational capacities. Intellectual and moral virtues represent different aspects of theoretical and practical rationality; we should cultivate them in accordance with the “Doctrine of the Mean.” For instance, courage lies at a wisdom-governed middle between a deficiency of courage, cowardice, and an excess of courage, rashness.
Stanford Encyclopedia of Philosophy, at http://plato.stanford.edu/entries/aristotle/
Pamela Stubbart, Program in Philosophy and Education, Teachers College, Columbia University