  So both parts of Kant’s philosophy are about autonomously constructing a world, but in different senses. In theoretical philosophy, we use our categories and forms of intuition to construct a world of experience or nature. In practical philosophy, we use the moral law to construct the idea of a moral world or a realm of ends that guides our conduct (4:433), and ultimately to transform the natural world into the highest good. Finally, transcendental idealism is the framework within which these two parts of Kant’s philosophy fit together (20:311). Theoretical philosophy deals with appearances, to which our knowledge is strictly limited; and practical philosophy deals with things in themselves, although it does not give us knowledge about things in themselves but only provides rational justification for certain beliefs about them for practical purposes.