Perhaps the most fundamental and distinctive idea of Kantian moral psychology is that no behavior can count as action unless it is performed on a subjective practical principle, or a maxim of action. The maxim is supposed to provide the target of moral assessment of all actions, whether this assessment is prospective or retrospective. The presence of a maxim is also supposed to illuminate how it is that agents are active in, hence responsible for, the peculiar species of events we (...) call actions. To put the point roughly, agents are the sources of their actions in that they have in some sense affirmed or endorsed the maxims of these actions. (shrink)