When Kant speaks about the moral law, he is essentially referring to that sense of obligation to which our will often responds. We all know the experience — we are sometimes pulled in a certain direction, not because we desire to act in that way, but in spite of our desire to act in the opposite way.
This pull is toward that moral sense which Kant believes each of us has, in virtue of being rational and free. It is conscience. Actually, it is deeper than conscience, because our conscience can be mistaken. Conscience arises because of certain structure of human consciousness — it is the structure of human reason and human will.
The Moral Order
Having mastered epistemology and metaphysics, Kant believed that a rigorous application of the same methods of reasoning would yield an equal success in dealing with the problems of moral philosophy. Thus, in the Kritik der practischen Vernunft (Critique of Practical Reason) (1788), he proposed a “Table of the Categories of Freedom in Relation to the Concepts of Good and Evil,” using the familiar logical distinctions as the basis for a catalog of synthetic a priori judgments that have bearing on the evaluation of human action, and declared that only two things inspire genuine awe: “der bestirnte Himmel über mir und das moralische Gesetz in mir” (“the starry sky above and the moral law within”). Kant used ordinary moral notions as the foundation ffor a derivation of this moral law in his Grundlegung zur Metaphysik der Sitten (Grounding for the Metaphysics of Morals) (1785).
From Good Will to Universal Law
We begin with the concept of that which can be conceived to be good without qualification, a good will. Other good features of human nature and the benefits of a good life, Kant pointed out, have value only under appropriate conditions, since they may be used either for good or for evil. But a good will is intrinsically good; its value is wholly self-contained and utterly independent of its external relations. Since our practical reason is better suited to the development and guidance of a good will than to the achievement of happiness, it follows that the value of a good will does not depend even on the results it manages to produce as the consequences of human action.
Kant’s moral theory is, therefore, deontological: actions are morally right in virtue of their motives, which must derive more from duty than from inclination. The clearest examples of morally right action are precisely those in which an individual agent’s determination to act in accordance with duty overcomes her evident self-interest and obvious desire to do otherwise. But in such a case, Kant argues, the moral value of the action can only reside in a formal principle or “maxim,” the general commitment to act in this way because it is one’s duty. So he concludes that “Duty is the necessity to act out of reverence for the law.”
According to Kant, then, the ultimate principle of morality must be a moral law conceived so abstractly that it is capable of guiding us to the right action in application to every possible set of circumstances. So the only relevant feature of the moral law is its generality, the fact that it has the formal property of universalizability, by virtue of which it can be applied at all times to every moral agent. From this chain of reasoning about our ordinary moral concepts, Kant derived as a preliminary statement of moral obligation the notion that right actions are those that practical reason would will as universal law.