It is generally recognized that actions are not truly moral if they are performed in conformity with duty but not for the sake of duty alone. Nevertheless, it is almost impossible to find examples of actions performed exclusively out of a sense of duty. Nearly every action we observe can be attributed to some motive other than pure duty. Indeed, it is often impossible to know whether even our own true motives are pure.

The lack of examples of pure moral action may seem disheartening. Yet we may take heart in the fact that all rational beings may recognize that reason imposes clear moral demands.

Furthermore, we should recognize that it would be impossible for us to derive universal moral laws from specific events and experiences; since all events are contingent upon specific circumstances, none of our experiences can be a source of moral principles that apply in all cases and all circumstances. Even our idea of God, the perfect being, is not based on experience, but rather on our a priori idea of moral perfection. Developing a clearer understanding of a priori moral concepts can help to reinforce our moral sense against the distractions of competing interests and motivations.

Rational beings may align their "will" either with the objective laws of reason and morality or with subjective needs and interests. Reason's demands may be called "imperatives." "Hypothetical imperatives" command that a particular action is necessary as a means to some purpose, such as the attainment of personal happiness. "Categorical imperatives" command that some action is necessary in and of itself.

Hypothetical imperatives are regular and obvious occurrences. Anytime someone settles upon some purpose or objective, reason may make clear to them what course of action they should pursue. This undertaking is more complicated in the case of indeterminate objectives like happiness, where it is difficult to know what particular actions will bring about the goal. Nevertheless, we have no problem understanding that people have chosen to act in a certain way as a result of a hypothetical imperative.

By contrast, we cannot find evidence for categorical imperatives in the decisions and actions we observe. People may appear to act in a certain way because of a pure demand of reason, yet we can never be sure that they do not have some circumstantial interest or ulterior motive other than a pure categorical imperative. Categorical imperatives must therefore be derived a priori.

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