Kant argued that moral requirements are based on a standard of rationality he dubbed the "Categorical Imperative" (CI). Immorality thus involves a violation of the CI and is thereby irrational. This argument was based on his striking doctrine that a rational will must be regarded as autonomous, or free in the sense of being the author of the law that binds it.

The fundamental principle of morality — the CI — is none other than this law of an autonomous will. Thus, at the heart of Kant's moral philosophy is a conception of reason whose reach in practical affairs goes well beyond that of a Humean ‘slave' to the passions. Moreover, it is the presence of this self-governing reason in each person that Kant thought offered decisive grounds
Kant's first formulation of the CI states that you are to "act only in accordance with that maxim through which you can at the same time will that it become a universal law."

First, formulate a maxim that enshrines your reason for acting as you propose. Second, recast that maxim as a universal law of nature governing all rational agents, and so as holding that all must, by natural law, act as you yourself propose to act in these circumstances. Third, consider whether your maxim is even conceivable in a world governed by this law of nature. If it is, then, fourth, ask yourself whether you would, or could, rationally will to act on your maxim in such a world. If you could, then your action is morally permissible.

Kant held that ordinary moral thought recognized moral duties toward ourselves as well as toward others. Hence, together with the distinction between perfect and imperfect duties, we recognize four categories of duties: perfect duties toward ourselves, perfect duties toward others, imperfect duties toward ourselves and imperfect duties toward others

Kant's example of a perfect duty to others concerns a promise you might consider making but have no intention of keeping in order to get needed money

At the heart of Kant's moral theory is the position that rational human wills