Kant's Moral Law: Groundwork of the Metaphysics of Morals ranks with Plato's Republic and Aristotle's Ethics as one of the most important works of moral philosophy ever written. In Moral Law, Kant argues that a human action is only morally good if it is done from a sense of duty, and that a duty is a formal principle based not on self-interest or from a consideration of what results might follow. From this he derived his famous and controversial maxim, the categorical imperative: "Act as if the maxim of your action were to become by your will a universal law of nature." H. J. Paton's translation remains the standard in English for this work. It retains all of Kant's liveliness of mind, suppressed intellectual excitement, moral earnestness, and pleasure in words. The commentary and detailed analysis that Paton provides is an invaluable and necessary guide for the student and general reader.