No.43 Referenced from ~ Part2 - Chapter 4 - Section 8

Consistent understanding of Kant's uudgment on the third antinomy

The "understanding," which is the ability to construct concepts from intuitive representations, is constrained by the sensibility through "schemas." In contrast, "reason," which is the ability to make inferences about concepts constructed by the understanding, is not constrained in this way. Therefore, the origin of "Transcendental Dialectic" is that inferences by reason teach us something that is not constrained by the objects given by sensuous intuition, that is, that they make it possible to recognize "things in themselves."

In order for cognition other than that of "phenomena" to be possible, it is necessary that there be a gap in the scope of cognition between the various functions that make up cognition. However, Kant denies this possibility, stating in "Schematism" that this state of affairs does not exist between sensibility and understanding. (B305)

However, this is not the case in the relationship between understanding and reason, and this kind of discrepancy exists, which is why reason exerts its original metaphysical orientation, uses infinite inference, and tries to fly freely from concepts. However, as a result, it is said that reason leads to paradoxes.