Freedom and practical reason › Reading responsibility through the argument

Return to the threatened witness. Kant's question is not whether a sufficiently vivid fear can influence behavior. It is whether fear determines everything the person has reason to do. Recognizing that false testimony should be refused supplies a different standpoint from predicting which desire will win.

For a careful reading, distinguish four questions: what principle is proposed, whether it can have the authority of a law, what actually determines the will, and what practical reason is entitled to assume. The answers concern different parts of the book. Mixing them can turn moral faith into a motive of reward, or turn uncertainty about behavior into a denial of obligation.

The second Critique joins moral responsibility to an account of reason's authority. Its challenge is to explain how an embodied, desiring agent can recognize a requirement that does not derive its validity from desire. The fact of reason names Kant's starting point; the rest of the book develops what accepting that starting point commits practical thought to.