To understand Kant’s arguments that practical philosophy justifies certain beliefs about things in themselves, it is necessary to see them in the context of his criticism of German rationalist metaphysics. The three traditional topics of Leibniz-Wolffian special metaphysics were rational psychology, rational cosmology, and rational theology, which dealt, respectively, with the human soul, the world-whole, and God. In the part of the Critique of Pure Reason called the Transcendental Dialectic, Kant argues against the Leibniz-Wolffian view that human beings are capable of a priori knowledge in each of these domains, and he claims that the errors of Leibniz-Wolffian metaphysics are due to an illusion that has its seat in the nature of human reason itself. According to Kant, human reason necessarily produces ideas of the soul, the world-whole, and God; and these ideas unavoidably produce the illusion that we have a priori knowledge about transcendent objects corresponding to them. This is an illusion, however, because in fact we are not capable of a priori knowledge about any such transcendent objects. Nevertheless, Kant attempts to show that these illusory ideas have a positive, practical use. He thus reframes Leibniz-Wolffian special metaphysics as a practical science that he calls the metaphysics of morals. On Kant’s view, our ideas of the soul, the world-whole, and God provide the content of morally justified beliefs about human immortality, human freedom, and the existence of God, respectively; but they are not proper objects of speculative  knowledge.[20]