In his doctrine of transcendental idealism, Kant argued the sum of all objects, the empirical world, is a complex of appearances whose existence and connection occur only in our representations.
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.
Aenesidemus, which I consider one of the most remarkable products of our decade, has convinced me of something which I admittedly already suspected: that even after the labors of Kant and Reinhold, philosophy is still not a science.
The inconsistencies in which Kant was involved through the faulty course taken by him in this respect were demonstrated to him by G. E. Schultze who in his ponderous and diffuse manner expounded the matter first anonymously in his Aenesidemus ... and then in his Kritik der theoretischen Philosophie.
[7]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.