  Many philosophers have held that external reasons are, in fact, harder to explain than internal ones; even some who were no skeptics about external reasons, like Immanuel Kant (see the entry on  Kant’s moral philosophy.)    So what makes external reasons so puzzling? One idea is that they are puzzling because they leave so little on the basis of which to explain why they are reasons for the people for whom they are reasons. Internal reasons are shared only by certain people—people with the requisite desires. So Max’s desires can be used to explain why he has the internal reasons that he has. But categorical external reasons like those Kant was concerned about (and which are required in order to reconcile Moral Rationalism with Moral Absolutism) are supposed to be reasons for any agent, no matter what she is like. So the only thing to which we can appeal in order to explain why Max has these reasons is the fact that Max is an agent. Some philosophers have accordingly invested great energy in developing robust enough accounts of agency to be able to explain moral reasons. For example, Christine Korsgaard (1996) maintains that reasons derive from the demands of autonomy, or being regulated by stable principles that define ones’ self, which she identifies as a necessary condition for acting at all.