The illusion is natural and inevitable, according to Kant.
Reason is the source of transcendent principles.
These principles are concocted by reason in its effort to unify the principles of the understanding by completing them. They employ Ideas, concepts whose intended objects are, as it were, free-standing, and which provide a foundation for the objects of experience. The basis of Wolff's division was this. Psychology's object is the soul, which is a special kind of contingent being. Cosmology concerns the world, which is the aggregation of all contingent beings which exist.