The Critique of Practical Reason

Immanuel Kant's The Critique of Practical Reason asks how reason can ground moral action without reducing ethics to appetite, advantage, or externally imposed reward. Published in 1788 as the second of his three Critiques, the book follows the limits placed on theoretical reason in the Critique of Pure Reason but reaches a different conclusion about practical thought. Pure theoretical reason must be restrained when it claims knowledge beyond possible experience; pure practical reason, Kant argues, can legitimately guide conduct through principles not derived from desire. Freedom becomes central because moral obligation would be unintelligible without the capacity to act under a law reason gives itself. God and immortality enter the argument as postulates required by practical reason, not as objects proven by the traditional ontological, cosmological, or teleological arguments Kant rejects. The book can stand apart from the Groundwork of the Metaphysics of Morals, yet it also answers objections to that earlier work. Its structure mirrors Kant's critical method: an Analytic studies the faculty's valid operation, a Dialectic examines its errors, and a Doctrine of Method addresses moral education. The Critique became a foundational text for deontological ethics because it locates moral worth in rational principle and autonomy instead of expected consequences.