What is morally permissible, and what is morally obligatory? These questions form the core of a vast amount of philosophical reasoning. In his Fundamental Principles of the Metaphysic of Morals, Immanuel Kant developed a basis for the answers.

Kant's test, known as the Categorical Imperative, is a logical proof of the Golden Rule and the centerpiece of this work. It constitutes his best-known contribution to ethical discussion, and a familiarity with his reasoning in this book is essential to students of philosophy, religion, and history.