No.61 Referenced from ~ Part2 - Chapter 2 - Section 4

The thing-in-itself is not a concept that is derived from phenomena by the law of the excluded middle of classical logic

The problem is that the division of "immanence/transcendence" that Kant derived as "phenomenon/thing-in-itself" is identified with the logical division of "knowable/unknowable". There is room for discussion as to whether the origins of the concepts of "phenomenon" and "thing-in-itself" are the same as the two logical domains of knowable/unknowable.

It can also be pointed out that Kant's repeated statement that "phenomena are not things in themselves" may be a negation as a "partial negation," which shows rather a relationship between the two, just as when he says that "salt water is not fresh water."

The distinction between "Or-thing-in-itself" and "And-thing-in-itself" mentioned at the end of "Part 2 Chapter 1 Break" also suggests that the understanding that there is a complete separation between phenomena and the thing itself may be incorrect. In addition, the multiplicity of meanings of the concept of negation in intuitionistic logic, which was explored in "Part 2 Chapter 4 Hard study," also seems to suggest the nature of the negation side of phenomena.