A Beginner's History of Philosophy, Vol. 2: Modern Philosophy

by Herbert Ernest Cushman

(1) Sense-perception has (a) a content of sense qualities, like sound, color, etc., and (b) the relations of space and time.

(2) Space and time originally belong to the subject as its forms of sense-perception, and are not introduced from without by experience.

(3) By means of space and time a priori knowledge is possible.

If there is any validity in perceptual knowledge, it depends upon the constitution of space and time; not upon the character of the empirical content, or the sensations. The question about the validity of sense-perception, then, is a question about the reliability of mathematics.

There are two elements in sense-perception: a necessary and constant, and a changing and accidental. Space and time are the constant element. They are homogeneous,and always one and the same in quality. They are unities, for there is only one space and one time, and the many spaces and times are only divisions of this oneness. All the differences in space and time are due to the relation and movements of bodies, and are not inherent in space and time themselves. How is this unity and homogeneity of space and time to be explained? By assuming that space and time are original and uniform functions of perception, the forms of perception, the ways of apprehension, the “prehensile organs of our sensibility.” They are the ways in which we synthesize on the lower level of consciousness. If they were given in experience, there is no reason why the several spaces and times should not be intrinsically different, like different bodies with different qualities. However, by conceiving them to be mental syntheses in the level of perception, they explain the universality of the laws of mathematics. They are the colored spectacles that all human beings wear; or, to use another figure, they are the mould into which all sensations are run. Being the unchangeable forms of our sensuous receptivity, they have a validity for the entire compass of perception. They are universal because one experience of space and time is valid for all spaces and times; they are necessary because we cannot think of objects apart from them; they are perceptual syntheses because they increase knowledge. Of course we are unconscious of this perceptual synthesis of the sensory elements in space and time. The process takes place automatically. We can nevertheless analyze the process after it has taken place, and speak of the sensations as the materials of knowledge, and the forms of space and time as the a priori elements. But in actualconscious experience, sensations never come to us in their rawness. They are never turned over to the understanding unless they bear the stamp of space and time. The process of knowledge, therefore, starts with complex material—complex because it has been synthesized below consciousness. In other words, perceptions come into the process of knowledge with two aspects: (1) their permanent and necessary form; and (2) their accidental and changing content.

2. In What does the Validity of the Understanding Consist? Kant’s discussion of the synthesis of the understanding is given in the Analytic, the second part of his Critique. His treatment of the understanding is similar to that of perception. The understanding, be it remembered, is regarded by Kant as the second stage in the process of a complete synthesis of knowledge. It is synthesis on a higher level than perception. Indeed, perception is the material which the understanding synthesizes. As in the Æsthetic Kant seeks to show: (1) the a priori factors of the understanding and (2) that these a priori factors give to knowledge its validity. The unifying principle of perception is the mathematical; but physical nature, which is the subject-matter of the study of the understanding, is more than mathematical, more than an aggregate of space and time forms, more than shapes and motions. Nature exists as a connected system of substances, causes, etc. Natural science possesses besides its mathematical basis a number of general a priori principles for the validity of its conclusions.

Kant’s task was therefore only begun by showing that perception possesses the universal and synthetic principles of space and time. Perception is only thebeginning of knowledge. It is not knowledge, but only subjective consciousness. On the other hand, the understanding is the faculty of knowledge, and therefore Kant seeks to point out its a priori or universal elements, and by their presence prove its validity.

Since the days of Aristotle the general terms used in reasoning have been called categories. Any class-term or genus may be called a category. There are certain summa genera, the most extensive classes or classes with the lowest connotation, that have been traditionally known as categories, because everything that can be affirmed in a judgment must come under some one or other of them. Aristotle names ten,—substance, quality, quantity, etc. But these Aristotelian categories are classes of analytical relations, such as formal logic treats. They are the classes of the attributes and relations into which objects may be analyzed. These evidently are not what Kant is seeking. He is in search of synthetic categories. He is looking for the synthetic forms of the understanding itself, which transform perceptions into objects of knowledge. He is not looking merely for abstract conceptions. For ideas become nature objects only when they are thought as things with qualities universal to every human mind. The understanding creates out of the perceptions the objects of thought which form the nature-world; and the categories of the understanding are the constitutive principles of such objects. The categories are the relating forms of synthesis through which objects arise. The most difficult part of the Critique is called the “Deduction of the Categories,” in which Kant attempts to derive the synthetic forms of the understanding from the various kinds of judgment. Kant’s list is curiousbut unimportant, and only two of these categories are useful,—substance and cause. He divides the categories into four general kinds and enumerates three categories of each of these kinds, as follows:—

Categories of Quantity,—Unity, Plurality, Totality.

Categories of Quality,—Reality, Negation, Limitation.