Thus Kant analyses the assumption of moral judgment. But it is still no more than an assumption, and he has to ask how it can be reconciled with the seemingly contradictory principle of causation. The analysis of the third antinomy in the first _Critique_, as we saw, prepared the way by maintaining that the same action might be phenomenally determined, and free as the action of a thing in itself, were there another form of causality--free causality or self-determination. For the existence of such another form of causality the first _Critique_ offered no evidence. Kant’s concern is to show that morality assumes it; for the claim of duty is that a man should not act as a creature of inclination, of likes and dislikes. Duty claims to cut across all such empirical considerations. The motive to do what duty demands must come from elsewhere. It may then be found to be a claim that man should act not as a part of the physical world, but as a moral being. For man, as well as an observer and understander of other men, is also a moral agent. As such he stands in quite different relations to other men. He treats them and himself as moral agents, responsible for their actions. As a member of the world of moral relations he acknowledges a system of rights and duties, he holds himself responsible to other men as they are responsible to him, and all this has nothing to do with what a man wants or does not want to do, with how easy or how difficult he may find it to perform what duty demands. In this he is assuming in himself and other men a power of determining the will in accordance with the moral law. That, just because it takes no account of likes and dislikes, cannot be derived from these or from considerations of circumstances or environment. It must be deducible from the nature of man as a moral being. In obeying the moral law, then, man will be obeying a law that comes from himself. His will will be self-legislative. This power of acting in accordance with a law that comes from the nature of man as a rational, responsible being, and not as a member of the world of causes and effects, is moral freedom; it is the assumption of all moral judgment and action. It cannot, Kant holds, be _explained_. For all explanation is the work of the understanding, and that can explain only phenomena. It is enough that the first _Critique_ has shown that phenomenal causality is not inconsistent with the possibility of another causality. In the moral sphere we act and judge as if we were free. The moral law and duty make claims upon us on the same assumption. Moral freedom, then, is the ground of the possibility of moral experience.