 Arthur Schopenhauer (1788–1860) heaped a great deal of invective on Fichte, Schelling, and Hegel. For that reason, Schopenhauer is not always included among the German idealists. And indeed, nothing could be further from Hegel’s version of absolute idealism than Schopenhauer’s theory on which behind the realm of appearances constructed in accordance with our own conceptions of space, time, and causality—his form of the empirical realism side of transcendental idealism—there is a unitary reality that is utterly irrational or at least arational—his form of Kant’s ontological realism, but flipped from practical to theoretical and from rational to arational. Nevertheless, since Schopenhauer works within a Kantian framework, and identifies underlying reality with pure activity, although of an arational rather than rational kind, it is useful to think of him within the framework of idealism.