Aenesidemus is a German book published anonymously by Professor Gottlob Ernst Schulze of Helmstedt in 1792.
Schulze attempted to refute the principles that Karl Leonhard Reinhold established in support of Immanuel Kant's Critique of Pure Reason (1781).
Its complete title, in English translation, was Aenesidemus or Concerning the Foundations of the Philosophy of the Elements Issued by Professor Reinhold in Jena Together with a Defense of Skepticism against the Pretensions of the Critique of Reason (German: Aenesidemus oder über die Fundamente der von dem Herrn Professor Reinhold in Jena gelieferten Elementar-Philosophie.
Nebst einer Vertheidigung des Skepticismus gegen die Anmassungen der Vernunftkritik).
Kant, however, was guilty of begging the question in that he presupposed that the thing-in-itself exists and causally interacts with observing subjects.
[2] If we were to take critical philosophy seriously, we would commit ourselves to resolving experiences into two parts — a system of universal subjective forms on one side, and a mass of amorphous, meaningless objective matter on the other.
Kant's response was indicated in his letter to Jakob Sigismund Beck, December 4, 1792: Reinhold wrote that true skepticism rested on the fact that only the observing subject felt what was in its consciousness.
Arthur Schopenhauer agreed with Schulze: ["Therefore the world as [REPRESENTATION], in which aspect alone we are here considering it, has two essential, necessary, and inseparable halves.