Immanuel Kant
On the concepts of pure reason

Kant calls the basic concepts of metaphysics "ideas". They are different from the concepts of understanding in that they are not limited by the critical stricture limiting knowledge to the conditions of possible experience and its objects. "Transcendental illusion" is Kant's term for the tendency of reason to produce such ideas. Although reason has a "logical use" of simply drawing inferences from principles, in "The Transcendental Dialectic", Kant is concerned with its purportedly "real use" to arrive at conclusions by way of unchecked regressive syllogistic ratiocination. The three categories of relation, pursued without regard to the limits of possible experience, yield the three central ideas of traditional metaphysics:

Although Kant denies that these ideas can be objects of genuine cognition, he argues that they are the result of reason's inherent drive to unify cognition into a systematic whole. Leibnizian-Wolffian metaphysics was divided into four parts: ontology, psychology, cosmology, and theology. Kant replaces the first with the positive results of the first part of the Critique. He proposes to replace the following three with his later doctrines of anthropology, the metaphysical foundations of natural science, and the critical postulation of human freedom and morality.
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