Kant's Theory of Knowledge

by H. A. Prichard

It is the aim of the Aesthetic to deal with the a priori knowledge which relates to the sensibility. This knowledge, according to Kant, is concerned with space and time. Hence he has to show firstly that our apprehension of space and time is a priori, i. e. that it is not derived from experience but originates in our apprehending nature; and secondly that within our apprehending nature this apprehension belongs to the sensibility and not to the understanding, or, in his language, that space and time are forms of perception or sensibility. Further, if his treatment is to be exhaustive, he should also show thirdly that space and time are the only forms of perception. This, however, he makes no attempt to do except in one passage,[1] where the argument fails. The first two points established, Kant is able to develop his main thesis, viz. that it is a condition of the validity of the a priori judgements which relate to space and time that these are characteristics of phenomena, and not of things in themselves.

It will be convenient to consider his treatment of space and time separately, and to begin with his treatment of space. It is necessary, however, first of all to refer to the term 'form of perception'. As Kant conceives a form of perception, it involves three antitheses.

(1) As a form of perception it is opposed, as a way or mode of perceiving, to particular perceptions.

(2) As a form or mode of perception it is opposed to a form or mode of conception.

(3) As a form of perception it is also opposed, as a way in which we apprehend things, to a way in which things are.

While we may defer consideration of the second and third antitheses, we should at once give attention to the nature of the first, because Kant confuses it with two other antitheses. There is no doubt that in general a form of perception means for Kant a general capacity of perceiving which, as such, is opposed to the actual perceptions in which it is manifested. For according to him our spatial perceptions are not foreign to us, but manifestations of our general perceiving nature; and this view finds expression in the assertion that space is a form of perception or of sensibility.[2]

Unfortunately, however, Kant frequently speaks of this form of perception as if it were the same thing as the actual perception of empty space.[3] In other words, he implies that such a perception is possible, and confuses it with a potentiality, i. e. the power of perceiving that which is spatial. The confusion is possible because it can be said with some plausibility that a perception of empty space—if its possibility be allowed—does not inform us about actual things, but only informs us what must be true of things, if there prove to be any; such a perception, therefore, can be thought of as a possibility of knowledge rather than as actual knowledge.

The second confusion is closely related to the first, and arises from the fact that Kant speaks of space not only as a form of perception, but also as the form of phenomena in opposition to sensation as their matter. "That which in the phenomenon corresponds to[4] the sensation I term its matter; but that which effects that the manifold of the phenomenon can be arranged under certain relations I call the form of the phenomenon. Now that in which alone our sensations can be arranged and placed in a certain form cannot itself be sensation. Hence while the matter of all phenomena is only given to us a posteriori, their form [i. e. space] must lie ready for them all together a priori in the mind."[5] Here Kant is clearly under the influence of his theory of perception.[6] He is thinking that, given the origination of sensations in us by the thing in itself, it is the business of the mind to arrange these sensations spatially in order to attain knowledge of the spatial world.[7] Space being, as it were, a kind of empty vessel in which sensations are arranged, is said to be the form of phenomena.[8] Moreover, if we bear in mind that ultimately bodies in space are for Kant only spatial arrangements of sensations,[9] we see that the assertion that space is the form of phenomena is only Kant's way of saying that all bodies are spatial.[10] Now Kant, in thus asserting that space is the form of phenomena, is clearly confusing this assertion with the assertion that space is a form of perception, and he does so in consequence of the first confusion, viz. that between a capacity of perceiving and an actual perception of empty space. For in the passage last quoted he continues thus: "I call all representations[11] pure (in the transcendental sense) in which nothing is found which belongs to sensation. Accordingly there will be found a priori in the mind the pure form of sensuous perceptions in general, wherein all the manifold of phenomena is perceived in certain relations. This pure form of sensibility will also itself be called pure perception. Thus, if I abstract from the representation of a body that which the understanding thinks respecting it, such as substance, force, divisibility, &c., and also that which belongs to sensation, such as impenetrability, hardness, colour, &c., something is still left over for me from this empirical perception, viz. extension and shape. These belong to pure perception, which exists in the mind a priori, even without an actual object of the senses or a sensation, as a mere form of sensibility." Here Kant has passed, without any consciousness of a transition, from treating space as that in which the manifold of sensation is arranged to treating it as a capacity of perceiving. Moreover, since Kant in this passage speaks of space as a perception, and thereby identifies space with the perception of it,[12] the confusion may be explained thus. The form of phenomena is said to be the space in which all sensations are arranged, or in which all bodies are; space, apart from all sensations or bodies, i. e. empty, being the object of a pure perception, is treated as identical with a pure perception, viz. the perception of empty space; and the perception of empty space is treated as identical with a capacity of perceiving that which is spatial.[13]

The existence of the confusion, however, is most easily realized by asking, 'How did Kant come to think of space and time as the only forms of perception?' It would seem obvious that the perception of anything implies a form of perception in the sense of a mode or capacity of perceiving. To perceive colours implies a capacity for seeing; to hear noises implies a capacity for hearing. And these capacities may fairly be called forms of perception. As soon as this is realized, the conclusion is inevitable that Kant was led to think of space and time as the only forms of perception, because in this connexion he was thinking of each as a form of phenomena, i. e. as something in which all bodies or their states are, or, from the point of view of our knowledge, as that in which sensuous material is to be arranged; for there is nothing except space and time in which such arrangement could plausibly be said to be carried out.

As has been pointed out, Kant's argument falls into two main parts, one of which prepares the way for the other. The aim of the former is to show firstly that our apprehension of space is a priori, and secondly that it belongs to perception and not to conception. The aim of the latter is to conclude from these characteristics of our apprehension of space that space is a property not of things in themselves but only of phenomena. These arguments may be considered in turn.