Chapter Five focuses on the concept of God and argues that Kant’s conception of a postulate has much more in common with the general nature of ideas of reason than it does with any claim to existence. Well before the Critique of Practical Reason, Kant developed the notion of a postulate along with the similar notions of transcendental hypothesis, idea of reason, and belief, each indicating various degrees of merely heuristic use of a concept. Kant’s position is unsettled in this development. In the second Critique, Kant’s discussion of the postulate of God continues to include ontological and merely heuristic elements. I show the plausibility of reading the postulate of God as having immanent reference, that is, to empirical agents’ moral lives, rather than transcendent reference, that is, to a being in itself. In the practical point of view empirical moral agents operate with the concept of God for certain purposes but relate it only to the ought, not to the is. Kant’s work after the second Critique, particularly the Opus Postumum, emphasize this use of the concept of God. The postulates thus fit within a metaphysical naturalism and a moral idealism.