Introduction: Freedom, Duty and Law

The system of the metaphysics of morals is divided into the doctrine of right and the doctrine of virtue — into the duties that can be externally enforced and those that cannot.

The faculty of desire in accordance with concepts, insofar as the ground determining it to action lies within itself and not in its object, is called a faculty of doing or refraining as one pleases. Insofar as it is joined with one's consciousness of the ability to bring about its object by one's action, it is called choice. The freedom of choice is its independence from being determined by sensible impulses; this is the negative concept of freedom. The positive concept is the capacity of pure reason to be of itself practical.

The laws of freedom, as distinguished from laws of nature, are called moral laws. Insofar as they are directed merely to external actions and their conformity to law, they are called juridical laws; but if they also require that they themselves be the determining grounds of actions, they are ethical laws. Conformity with the first is legality; with the second, morality.

All lawgiving can therefore be distinguished with respect to the incentive. Lawgiving which makes an action a duty, and also makes this duty the incentive, is ethical. But lawgiving which does not include the incentive of duty in the law, and so admits an incentive other than the idea of duty itself, is juridical. So I may keep a promise because I fear the law, and this is enough for right; but to keep it because it is my duty is virtue.

Kant's distinction between "right" (Recht), which concerns outward actions and can be enforced, and "virtue" (Tugend), which concerns inner motives and cannot, is the basis of the whole work.

The supreme principle of the doctrine of morals is: act on a maxim which can also hold as a universal law. Any maxim that does not so qualify is contrary to morals.