F. H. Jacobi The first to criticize the concept of a thing-in-itself was
F. H. Jacobi, with the expression:
G. E. Schulze The anonymously published work
Aenesidemus was one of the most successful attacks against the project of Kant. According to Kant's teaching, things-in-themselves cannot cause appearances, since the
category of
causality can only find application to objects of experience. Kant, therefore, does not have the right to claim the existence of things-in-themselves. This contradiction was subsequently generally accepted as being the main problem of the thing-in-itself. The attack on the thing-in-itself, and the skeptical work in general, had a big impact on
Fichte, and
Schopenhauer called
G. E. Schulze, who was revealed to be the author, “the acutest" of Kant's opponents.
Johann Gottlieb Fichte Initially
Fichte embraced
Kantian philosophy, including a thing-in-itself, but the work of Schulze made him revise his position. The system which Fichte subsequently published,
Science of Knowledge, scraps the thing-in-itself.
Schopenhauer In his "
Critique of the Kantian Philosophy" appended to
The World as Will and Representation (1818),
Arthur Schopenhauer agreed with the critics that the manner in which Kant had introduced the thing-in-itself was inadmissible, but he considered that Kant was right to assert its existence and praised the distinction between thing-in-itself and appearance as Kant's greatest merit. As he wrote in volume 1 of his
Parerga and Paralipomena, "Fragments of the History of Philosophy," §13:
Mainländer A unique position is taken by
Philipp Mainländer, who hailed Kant for breaking the rules of his own philosophy to proclaim the existence of a thing-in-itself. ==See also==