Act Only According To That Maxim

This is Kant's first formulation of the Categorical Imperative, from the Groundwork of the Metaphysics of Morals (1785), Section II. It is his attempt to derive a universal principle of morality from reason alone, without appeal to God, consequences, or human desire. The test Kant proposes — can your maxim become a universal law without contradiction? — was intended to replace the "Golden Rule" with a more rigorous rational foundation and remains the most discussed principle in modern ethics.