" Kant himself betrays his consciousness of the untenable nature of his doctrine of the categories by the fact that in the third chapter of the Analytic of Principles (phaenomena et noumena) several long passages of the first edition (p. 241, 242, 244-246, 248-253) are omitted in the second - passages which displayed the weakness of that doctrine too openly. So, for example, he says there (p. 241) that he has not defined the individual categories, because he could not define them even if he had wished to do so, inasmuch as they were susceptible of no definition. In saying this he forgot that at p. 82 of the same first edition he had said: 'I purposely dispense with the definition of the categories although I may be in possession of it." This then was, sit venia verbo, wind. But this last passage he has allowed to stand. And so all those passages wisely omitted afterwards betray the fact that nothing distinct can be thought in connection with the categories, and this whole doctrine stands upon a weak foundation. "

― Arthur Schopenhauer , The World as Will and Representation, Vol. 2