In the Transcendental Dialectic, Kant formulates a principle he calls the “supreme principle of pure reason” (hereafter, ‘SP’). According to SP, if a conditioned object is given, then the whole series of its conditions and hence something unconditioned is also given (A308/B365). Most interpreters take SP to be Kant’s rendering of the rationalist’s Principle of Sufficient Reason (hereafter, ‘PSR’), which says that everything has a sufficient reason that explains why it is the way it is. I argue that this obscures (...) an important distinction in Kant’s philosophy between two different explanatory demands. For Kant, SP’s demand for unconditioned conditions expresses a demand for what I call explanatory completeness, i.e., for explanations to come to an end in things that do not require explanation. In contrast, the PSR as Kant understands it expresses a demand for what I call exceptionless explicability, i.e., for nothing to lack an explanation. These demands are not the same, and they even stand in tension in Kant’s view if neither is subject to restriction. Once we see this, we better understand the predicament Kant thinks we face as rational inquirers who seek both explanatory completeness and exceptionless explicability. (shrink)