Critique of the Kantian philosophy
"Critique of the Kantian philosophy" is a criticism Arthur Schopenhauer appended to the first volume of his "The World as Will and Representation" (1818). He wanted to show Immanuel Kant's errors so that Kant's merits would be appreciated and his achievements furthered.
Otto Liebmann
A forerunner of Neo-Kantianism, in his best-known book, "Kant und die Epigonen", he deals with the philosophy after Kant, discussing Fichte, Schelling, Hegel, Fries, Herbart and Schopenhauer. Having credited Kant's philosophy (though criticizing it on the vital point of accepting a thing-in-itself), he focuses on what he sees as the shortcomings in the approaches of Kants successors. He frequently ends a section with the statement that one should return to Kant.