If we wish to regard the world in the light of the "thing itself," we shall easily see that the world "itself" and the world as it appears, the world of phenomena, differ only in the same way in which the whole differs from its component parts. The world "itself" is nothing else but the sum total of its phenomena. The same holds good of that part of the world phenomena which we call reason, spirit, faculty of thought. Although we distinguish between the faculty of thought and its phenomena or manifestations, yet the faculty of thought "itself," or "pure" reason, exists in reality only in the sum total of its manifestations. Seeing is the physical existence of the faculty of sight. We possess the whole only by means of its parts, and we can possess reason, like all other things, only by the help of its effects, by its various thoughts. But we repeat that reason does not precede thought in the order of time. On the contrary thoughts generated by perceptible objects serve as a basis for the development of the concept of the faculty of thought. Just as the understanding of the world movements has taught us that the sun is not revolving around the earth, so the understanding of the thought process tells us that it is not the faculty of thought which creates thought, but vice versa, that the concept of this faculty is created out of a series of concrete thoughts. Hence the faculty of thought practically exists only as the sum total of our thoughts, just as the faculty of sight exists only through the sum of the things that we see.
These thoughts, this practical reason, serve as the material out of which our brain manufactures the concept of "pure" reason. Reason is necessarily impure in practice, which means that it must connect itself with some object. Pure reason, or abstract reason without any special content, cannot be anything else but the general characteristic of all concrete reasoning processes. We possess this general nature of reason in two ways: In an impure state, that is as practical and concrete phenomenon, consisting of the sum of our real perceptions, and in a pure state, that is theoretically or abstractly, in the concept. The phenomenon of reason is distinguished from reason "itself" just as the real animals are distinguished from the concept of the animal.
Every actual reasoning process is based on some real object which has many qualities like all things in nature. The faculty of thought extracts from this many-sided object those properties which are general or common with it. A mouse and an elephant, as the objects of our reasoning activity, lose their differences in the general animal concept. Such a concept combines many things under one uniform point of view, it develops one general idea out of many concrete things. Since understanding is the general or common quality of all reasoning processes, it follows that reason in general, or the general nature of the reasoning process, consists in abstracting the general ideal character from any concrete thing perceptible by the help of the senses.
Reason being unable to exist without some objects outside of itself, it is understood that we can perceive "pure" reason, or reason "itself," only by its practical manifestations. We cannot find reason without objects outside of it with which it comes in contact and produces thought, any more than we can find any eyes without light. And the manifestations of reason are as varied as the objects which supply its material. It is plain, then, that reason has no separate existence "in itself," but that on the contrary the concept of reason is formed out of the material supplied by the senses.
Mental processes appear only in connection with perceptible phenomena. These processes are themselves phenomena of sense perception which, in connection with a brain process, produce the concept of the faculty of thought "itself." If we analyze this concept, we find that "pure" reason consists in the activity of producing general ideas out of concrete materials, which include so-called immaterial thoughts. In other words, reason may be characterized as an activity which seeks for unity in every multiplicity and equalizes all contrasts whether it deals with the many different sides and parts of one or of more objects. All these different statements describe the same thing in different words, so that the reader may not cling to the empty word, but grasp the living concept, the manifold object, in its general nature.
Reason, we said, exists in a "pure" state as the development of the general out of the special, of the abstract out of concrete sense perceptions. This is the whole content of pure reason, of scientific understanding, of consciousness. And by the terms "pure" and "whole" we simply indicate that we mean the general content of the various thought processes, the general form of reason. Apart from this general abstract form, reason, like all other things, has also its concrete, special, sense form which we perceive directly through our experience. Hence our entire process of consciousness consists in the experience of the senses, that is in the physical process, and its understanding. Understanding is the general reflection of any object.
Consciousness, as the Latin root of the word indicates, is the knowledge of being in existence. It is a form, or a quality, of existence which differs from other forms of being in that it is aware of its existence. Quality cannot be explained, but must be experienced. We know by experience that consciousness includes along with the knowledge of being in existence the difference and contradiction between subject and object, thinking and being, between form and content, between phenomenon and essential thing, between attribute and substance, between the general and the concrete. This innate contradiction explains the various terms applied to consciousness, such as the organ of abstraction, the faculty of generalization or unification, or in contradistinction thereto the faculty of differentiation. For consciousness generalizes differences and differentiates generalities. Contradiction is innate in consciousness, and its nature is so contradictory that it is at the same time a differentiating, a generalizing, and an understanding nature. Consciousness generalizes contradiction. It recognizes that all nature, all being, lives in contradictions, that everything is what it is only in co-operation with its opposite. Just as visible things are not visible without the faculty of sight, and vice versa the faculty of sight cannot see anything but what is visible, so contradiction must be recognized as something general which pervades all thought and being. The science of understanding, by generalizing contradiction, solves all concrete contradictions.