History of Western Philosophy - Bertrand Russell [406]
C. KANT'S THEORY OF SPACE AND TIME
The most important part of The Critique of Pure Reason is the doctrine of space and time. In this section I propose to make a critical examination of this doctrine.
To explain Kant's theory of space and time clearly is not easy, because the theory itself is not clear. It is set forth both in The Critique of Pure Reason and in the Prolegomena; the latter exposition is the easier, but is less full than that in the Critique. I will try first to expound the theory, making it as plausible as I can; only after exposition will I attempt criticism.
Kant holds that the immediate objects of perception are due partly to external things and partly to our own perceptive apparatus. Locke had accustomed the world to the idea that the secondary qualities—colours, sounds, smells, etc.—are subjective, and do not belong to the object as it is in itself. Kant, like Berkeley and Hume, though in not quite the same way, goes further, and makes the primary qualities also subjective. Kant does not at most times question that our sensations have causes, which he calls 'things-in-themselves' or 'noumena'. What appears to us in perception, which he calls a 'phenomenon', consists of two parts: that due to the object, which he calls the 'sensation', and that due to our subjective apparatus, which, he says, causes the manifold to be ordered in certain relations. This latter part he calls the form of the phenomenon. This part is not itself sensation, and therefore not dependent upon the accident of environment; it is always the same, since we carry it about with us, and it is a priori in the sense that it is not dependent upon experience. A pure form of sensibility is called a 'pure intuition' (Anschauung); there are two such forms, namely space and time, one for the outer sense, one for the inner.
To prove that space and time are a priori forms, Kant has two classes of arguments, one metaphysical, the other epistemological, or, as he calls it, transcendental. The former class of arguments are taken directly from the nature of space and time, the latter indirectly from the possibility of pure mathematics. The arguments about space are given more fully than those about time, because it is thought that the latter are essentially the same as the former.
As regards space, the metaphysical arguments are four in number.
(1) Space is not an empirical concept, abstracted from outer experiences, for space is presupposed in referring sensations to something external, and external experience is only possible through the presentation of space.
(2) Space is a necessary presentation a priori, which underlies all external perceptions; for we cannot imagine that there should be no space, although we can imagine that there should be nothing in space.
(3) Space is not a discursive or general concept of the relations of things in general, for there is only one space, of which what we call 'spaces' are parts, not instances.
(4) Space is presented as an infinite given magnitude, which holds within itself all the parts of space; this relation is different from that of a concept to its instances, and therefore space is not a concept but an Anschauung.
The transcendental argument concerning space is derived from geometry. Kant holds that Euclidean geometry is known a priori, although it is synthetic, i.e. not deducible from logic alone. Geometrical proofs, he considers, depend upon the figures; we can see, for instance, that, given two intersecting straight lines at right angles to each other, only one straight line at right angles to both can be drawn through their point of intersection. This knowledge, he thinks, is not derived from experience. But the only way in which my intuition can anticipate what will be found in the object is if it contains only the form of my sensibility, antedating in my subjectivity all the actual impressions. The objects of sense must obey geometry, because geometry is concerned with our ways of perceiving, and therefore we cannot perceive otherwise. This explains why geometry, though