Kant taught that an action could only count as the action of a good will if it satisfied the test of the Categorical Imperative. Kant's version of duty-based ethics was based on something that he ...

Although our own will is the source of value, Kant is not a subjectivist: Need two modes of evaluation: an action has moral worth if it is done for the sake of duty. an action is morally correct if ...

He called this the "categorical imperative." Today we would formulate it like this: You should only do what is the best for all. In 1781, Kant published what is probably his most important work.