The author aims to vindicate the widely held belief -- recently doubted by philosophers, however -- that the most important truths of morality can be identified by the natural reasoning faculties of human beings. The author argues that those requirements which reasonable people regard as necessary to protect them against subjugation amount to a complete set of justice principles. According to the author, reason requires us to refrain from subjugating one another; thus, justice principles are requirements of reason. Further, the author reasons that the concept of justice, which emerges from what prevents subjugation, expresses the underlying rationale of the social-contract tradition in moral philosophy. Interwoven with the author's argument for justice as reason's answer to subjugation is an interpretation of the history of contractarian moral theory from Hobbes to Rawls. The author's theory indicates what is correct in Rawl's "A Theory of Justice" and identifies its flaw in not indicating what justice provides as reason's answer to subjugation. Chapter notes, subject index.