Theory of the Moral System: Including a Possible Reason Why Sin Exists is a philosophical treatise written by Ezra Hall Gillett and originally published in 1855. The book explores the nature of morality and attempts to provide a comprehensive theory of the moral system. Gillett argues that morality is based on the idea of duty, and that moral principles are universal and objective. He also delves into the concept of sin, examining why it exists and...