One of Kant’s categories—a priori concepts the possession and applicability of which are necessary conditions of possible experience—is a concept of necessity. But it is unclear why the concept of necessity, as Kant defines it, should be a category thus understood. My aim is to offer a reading of Kant that fills this lacuna: the category of necessity is required to make necessity as it features in the world of experience understandable: a concept that the understanding can grasp and employ (...) in cognition of objects. Kant’s view has potential wider significance for accounts of the function of necessity judgments. (shrink)