The laws of the freedom are called moral laws and while, according to Kant, they say respect only to the exterior actions, and its legality: they are called legal; but, if they also demand that these laws must be the principles of determination of the actions, they are ethical. In the Metaphysics of the customs, Kant strengthens in the classic distinction between the moral legislation and the legal one. as starting point indicates the initial problem of the legal philosophy, that is the distinction between both. In this direction, what effectively it distinguishes the two legislaes is not only the fact of a legislation to be internal and to another external one, but specifically the idea of the duty as impulse. Therefore, to understand this idea, it must be considered that better all legislation possesss two constituent elements, which is: the objective element that means the representation of the law as necessary to the action and that in such a way it converts the action into having, and a subjective element that binds the representation of the law to the bedding of determination of the will for accomplishment of such action. At the first moment, it is had what Kant called of theoretical knowledge of the possibility of practical rule e, in as, the duty as impulse.
The implication more immediate of this distinction it is the fact of that the characteristic duties of the legal legislation are external, therefore do not demand the idea of an interior duty. Moral in ample direction understands the doctrine of the customs in such a way englobando the right how much the ethics, the first one is the proper a legality, the correspondence to the legal law; the second a morality, the ethical conscience. For Kant some concepts are common to the two parts of the metaphysics of the customs, between them, the duty and the obligation.