The topic that I wish to consider is that of the significance, both systematic and historical, for Kant's system as a whole of the postulates of pure practical reason, more specifically, of the two theological postulates concerning the existence of God and personal immortality which form the basis of Kant's moral theology. My discussion will proceed by way of an examination of the problems of Kant's moral theology in the eyes of his early contemporaries, for whom it constituted a crux in Kant's project. Different views were taken by Kant's contemporaries of what exactly follows from this regarding the coherence and completeness of Kant's Critical philosophy. For the thinkers I will be looking at here, the miscarriage of the moral theology constituted a fatal fault in Kantianism. For the German Idealists, the moral theology instead provided a vital clue as to how the Kantian system could be, and showed why it needed to be, transformed into a more radical idealism. The role of the practical postulates in the development of German Idealism demands a separate treatment; what I will argue here is simply that the practical postulates do indeed represent a point at which Kant's philosophical system displays a deep and interesting tension, in light of which both historical responses are prima facie intelligible
