"Among the important books in the history of American legal philosophy.  It includes insights into the relations between morality and law, and advances a theory of law of great practical relevance. . . . [This] is the best discussion of the demands of the rule of law in existing literature."—Robert S. Summers, Journal of Legal Education "Throughout this profound, imaginative and keenly analytical work, [Fuller] demonstrates his continuing concern with the tension in morality and law between the 'is' and the 'ought'. . . . A book of ideas should . . . provoke and contribute new thoughts. This book does both."—Barry R. Mandelbaum, New York Law Forum In this classic work the legal philosopher Lon L. Fuller explores the relationship between law and morality, distinguishing between the morality of duty and the morality of aspiration.