Abstract: Perfectionism is one of the leading moral views of the Western tradition, defended by Plato, Aristotle, Aquinas, Leibniz, Hegel, Marx, Nietzsche, and Green. Defined broadly, it holds that what is right is whatever most promotes certain objective human goods such as knowledge, achievement, and deep personal relations. Defined more narrowly, it identifies these goods by reference to human nature, so the human good consistsin developing the properties fundamental to human beings. If it is fundamental to humans to be rational (Aristotle), to labor (Marx), or to exercise power (Nietzsche), developing these traits is best. This book tries to formulate the most defensible version of perfectionism using contemporary analytic techniques. It first examines narrow perfectionism, asking what kind of properties human nature consists in (distinctive? essential?); how these properties are identified; and what they are. It then explores issues relevant to both broad and narrow perfectionism, including whether each person should pursue just his own perfection or everyone's; how perfectionist goods are compared and aggregated; and in what particular times they are. On the last topic it develops an “Aristotelian” theory of the value of theoretical and practical rationality, as embodied in beliefs and ends with specified formal properties. The book closes by examining perfectionism's implications for political questions about liberty and equality.

Keywords: achievement, Aristotle, equality, ethics, good, human nature, knowledge, liberty, morality, objective, perfectionism, rationality, value