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Schopenhauer (& Kantian metaphysics): *
In his "Critique of the Kantian Philosophy" (appended to The World as Will and Representation) Schopenhauer stated that Kant was right to assert “the thing-in-itself “& praised Kant's distinction between phenomenon & noumenon. However he also agreed with the critics, that Kant’s explanation of “the thing-in-itself” was inadmissible. In Parerga and Paralipomena (1851) he states while Kant was right to assert a thing-in-itself from which every phenomenon derives its existence, he derived the truth of this from the given representation itself (the phenomenon) combined with the a priori laws or categories, specifically the law of causality. As an a priori category, causality only supplies knowledge when applied to the field of possible experience & not outside it. Since the noumenon is by definition outside experience, using causality to prove its existence is logically incorrect.
To grasp the noumenon we need an entirely different course, which Schopenhauer claims is found with introspection- inner awareness, starting with your body. It is both object but also a manifestation of Will. Schopenhauer replaces noumenon with Will. Observable reality is an expression of Will, each individual is an expression of their own personal Will. Will is not rational however but is endless striving, blind impulse with no end in view, devoid of knowledge, lawless, absolutely free, entirely self-determining & almighty. In the world as Will, there is no God to comprehend, the world is inherently meaningless. Will controls the actions, appetites & emotions and while people are capable of understanding Will, few do. Schopenhauer was building on the transcendental idealism of Kant, but developed an atheistic metaphysical & ethical system that rejected German idealism. Schopenhauer maintains that we create the violent state of nature, the individuation we impose upon things, is imposed upon a blind striving energy that, once it becomes individuated and objectified, turns against itself, consumes itself, and does violence to itself.
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Nietzsche (and materialism): *
In 1866 a young Nietzsche read Friedrich Albert Lange's History of Materialism. He was intrigued greatly by the rise of Materialism & science, Darwin's theory of evolution & the rebellion against tradition and authority. Years later, in The Gay Science (1882) he extolled the merits of science & scepticism. Nietzsche had no time for metaphysics; he attacked the thing in itself (Kant) and cogito ergo sum (Descartes) as un-falsifiable beliefs based on naive acceptance of previous notions and fallacies. In Beyond Good and Evil he promoted over all else the science of psychology, what he called “the queen of the sciences” which was “on the path to the fundamental problems.”
Probably the most critical assessment in terms of his materism is found in The Will to Power where he sketches out his “Perspectivism,” a clear rejection of objective metaphysics, claiming no evaluation of objectivity can transcend cultural formations or subjective designations;, there are no objective facts, nor any knowledge of a thing-in-itself. There are no ethical or epistemological absolutes. Rules, be they of science of philosophy are constantly reassessed according to circumstances. Today’s “Truth” is created by integrating different vantage points together. This idea, that one value-system is no more worthy than the next, has become a common premise in modern social science.