Freedom and practical reason › Maxims and laws

Kant distinguishes a maxim from a practical law. A maxim is an agent's subjective principle of action. It says what the person proposes to do under certain circumstances and for what end. A practical law claims objective validity for rational agents, rather than expressing one person's preference.

A maxim is therefore more informative than an isolated action label. "I will borrow money" leaves out the circumstances and purpose. "When I need money, I will obtain it by making a promise I intend to break" identifies a proposed way of acting. Moral assessment concerns that principle, not just the outward movement of signing a document.

In the second Critique, Kant formulates the fundamental law through universal legislation: act so that the maxim of your will could also hold as a principle of legislation for everyone. The demand concerns what a rational will can legislate, rather than what an individual happens to find acceptable.

This formulation should not be confused with asking whether a behavior is popular. A practice could be widespread and still rest on a principle that cannot justify itself as a law for everyone. Nor is the test simply whether the agent would enjoy the outcome. Kant's question is about the authority of the principle from which the person acts.