Deontology and categorical imperative:

In deontological ethics an action is considered morally good because of some characteristic of the action itself, not because the product of the action is good. Deontological ethics holds that at least some acts are morally obligatory regardless of their consequences for human welfare. Descriptive of such ethics are such expressions as “Duty for duty’s sake,” “Virtue is its own reward,” and “Let justice be done though the heavens fall.”

By contrast, teleological ethics (also called consequentialist ethics or consequentialism) holds that the basic standard of morality is precisely the value of what an action brings into being. Deontological theories have been termed formalistic, because their central principle lies in the conformity of an action to some rule or law.

The first great philosopher to define deontological principles was Immanuel Kant, the 18th-century German founder of critical philosophy (see Kantianism). Kant held that nothing is good without qualification except a good will, and a good will is one that wills to act in accord with the moral law and out of respect for that law rather than out of natural inclinations. He saw the moral law as a categorical imperative—i.e., an unconditional command—and believed that its content could be established by human reasonalone. Thus, the supreme categorical imperative is: “Act only on that maxim through which you can at the same time will that it should become a universal law.” Kant considered that formulation of the categorical imperative to be equivalent to: “So act that you treat humanity in your own person and in the person of everyone else always at the same time as an end and never merely as means.” The connection between those two formulations, however, has never been entirely clear. In any event, Kant’s critics questioned his view that all duties can be derived from a purely formal principle and argued that, in his preoccupation with rational consistency, he neglected the concrete content of moral obligation.