This chapter looks at Kant’s understanding of the relationship between laws of nature and those of freedom in order to further explain Kant’s grounding argument at 4:453. The two sets of laws constitute two systems, the first governing phenomenal nature and the second the intelligible world, that is, the systematic interrelation of rational wills. How the two sets of laws relate reveal one fundamental philosophical system that can be grasped correctly only from the standpoint of practical reason, namely, that of the agent making use of its intelligence in its practical activity. It is the same understanding and the very same transcendental subject who gives the law to nature, who also gives the law to itself, using the same set of concepts, only differently applied. Our law-giving function in both worlds grounds the primacy of our membership in the intelligible world. Different criteria of application of these concepts to noumenal and phenomenal worlds are discussed, and I show how Kant avoids objections to the idea of timeless agency. Kant espouses a modified Leibizianism through which the intelligible and sensible worlds are harmonized indirectly by the author of nature, who harmonizes the functions in us through which the two are constituted.