Arthur Schopenhauer - Influences - Criticism of Kant

Criticism of Kant

Main article: Schopenhauer's criticism of the Kantian philosophy See also: On the Basis of Morality and Schopenhauer's criticism of Kant's schemata

Schopenhauer accepted Kant's double-aspect of the universe — the phenomenal (world of experience) and the noumenal (the true world, independent of experience). Some commentators suggest that Schopenhauer claimed that the noumenon, or thing-in-itself, was the basis for Schopenhauer's concept of the will. Other commentators suggest that Schopenhauer considered will to be only a subset of the "thing-in-itself" class, namely that which we can most directly experience.

Schopenhauer's identification of the Kantian noumenon (i.e., the actually existing entity) with what he termed "will" deserves some explanation. The noumenon was what Kant called the Ding an Sich, the "Thing in Itself", the reality that is the foundation of our sensory and mental representations of an external world. In Kantian terms, those sensory and mental representations are mere phenomena. Schopenhauer departed from Kant in his description of the relationship between the phenomenon and the noumenon. According to Kant, things-in-themselves ground the phenomenal representations in our minds; Schopenhauer, on the other hand, believed phenomena and noumena to be two different sides of the same coin. Noumena do not cause phenomena, but rather phenomena are simply the way by which our minds perceive the noumena, according to the Principle of Sufficient Reason. This is explained more fully in Schopenhauer's doctoral thesis, On the Fourfold Root of the Principle of Sufficient Reason.

Schopenhauer's second major departure from Kant's epistemology concerns the body. Kant's philosophy was formulated as a response to the radical philosophical skepticism of David Hume, who claimed that causality could not be observed empirically. Schopenhauer begins by arguing that Kant's demarcation between external objects, knowable only as phenomena, and the Thing in Itself of noumenon, contains a significant omission. There is, in fact, one physical object we know more intimately than we know any object of sense perception: our own body.

We know our human bodies have boundaries and occupy space, the same way other objects known only through our named senses do. Though we seldom think of our body as a physical object, we know even before reflection that it shares some of an object's properties. We understand that a watermelon cannot successfully occupy the same space as an oncoming truck; we know that if we tried to repeat the experiment with our own body, we would obtain similar results – we know this even if we do not understand the physics involved.

We know that our consciousness inhabits a physical body, similar to other physical objects only known as phenomena. Yet our consciousness is not commensurate with our body. Most of us possess the power of voluntary motion. We usually are not aware of the breathing of our lungs or the beating of our heart unless somehow our attention is called to them. Our ability to control either is limited. Our kidneys command our attention on their schedule rather than one we choose. Few of us have any idea what our liver is doing right now, though this organ is as needful as lungs, heart, or kidneys. The conscious mind is the servant, not the master, of these and other organs; these organs have an agenda which the conscious mind did not choose, and over which it has limited power.

When Schopenhauer identifies the noumenon with the desires, needs, and impulses in us that we name "will," what he is saying is that we participate in the reality of an otherwise unachievable world outside the mind through will. We cannot prove that our mental picture of an outside world corresponds with a reality by reasoning; through will, we know – without thinking – that the world can stimulate us. We suffer fear, or desire: these states arise involuntarily; they arise prior to reflection; they arise even when the conscious mind would prefer to hold them at bay. The rational mind is, for Schopenhauer, a leaf borne along in a stream of pre-reflective and largely unconscious emotion. That stream is will, and through will, if not through logic, we can participate in the underlying reality beyond mere phenomena. It is for this reason that Schopenhauer identifies the noumenon with what we call our will.

In his criticism of Kant, Schopenhauer claimed that sensation and understanding are separate and distinct abilities. Yet, for Kant, an object is known through each of them. Kant wrote: "... here are two stems of human knowledge ... namely, sensibility and understanding, objects being given by the former and thought by the latter ." Schopenhauer disagreed. He asserted that mere sense impressions, not objects, are given by sensibility. According to Schopenhauer, objects are intuitively perceived by understanding and are discursively thought by reason (Kant had claimed that (1) the understanding thinks objects through concepts and that (2) reason seeks the unconditioned or ultimate answer to "why?"). Schopenhauer said that Kant's mistake regarding perception resulted in all of the obscurity and difficult confusion that is exhibited in the Transcendental Analytic section of his critique.

Lastly, Schopenhauer departed from Kant in how he interpreted the Platonic ideas. In The World as Will and Representation Schopenhauer explicitly stated:

...Kant used the word wrongly as well as illegitimately, although Plato had already taken possession of it, and used it most appropriately.

Instead Schopenhauer relied upon the Neoplatonist interpretation of the biographer Diogenes Laërtius from Lives and Opinions of Eminent Philosophers. In reference to Plato’s Ideas, Schopenhauer quotes Laërtius verbatim in an explanatory footnote.

Diogenes Laërtius (III, 12) Plato ideas in natura velut exemplaria dixit subsistere; cetera his esse similia, ad istarum similitudinem consistencia. (Plato teaches that the Ideas exist in nature, so to speak, as patterns or prototypes, and that the remainder of things only resemble them, and exist as their copies.)