The mind, then, has a faculty of sensible receptivity (sensibility) through which it has the power to form pure intuitions. We have seen this power illustrated by the above thought-experiment; and Kant will later claim that it is crucially at work in the construction of geometrical figures and arithmetical products. He holds that the mind possesses two forms of sensible intuition: that by which extension and figure are represented is called ‘outer intuition’, and that by which succession and the simultaneous are represented is called ‘inner intuition’. It is because the mind possesses these two a priori forms of sensible intuition that it can also become conscious of appearances – that is, of empirical intuitions.When the object which exists independently of the mind (the thing in itself, or transcendental object) affects our sensibility, we become conscious of appearance(s) in outer or inner intuition: in other words, we have an outer or inner empirical intuition.
Space and time
Now the key question is: When we perceive objects in space or time, what is the relationship between this space or time (and so spatial or temporal objects), on the one hand, and our forms of outer or inner intuition (and so appearances), on the other? Restricting the possibilities to space, does space exist independently of any property of our mind and, hence, of outer intuition? If so, space must either exist in itself or be a relation between things in themselves. In either case, our perceptual knowledge of spatial objects would have to be gained by means of an inference from what exists in the mind, i.e. by means of an inference from appearances in our outer intuition to spatial objects existing outside the mind. Or is space to be identified with a property of our mind – that is, with pure outer intuition? If so, our perceptual knowledge of spatial objects will be the same as, or at least a subset of, our knowledge of appearances in outer intuition. On this latter alternative, no inference to what exists outside the mind, viz. to things in themselves, would be required for gaining perceptual knowledge. Similar questions and replies go for time.
When Kant specifically turns to discuss space and time, rather than the forms of our intuition, he immediately signals that what concerns him is how space and time are related to our outer and inner intuitions: ‘What then are space and time? Are they real existences? Are they only determinations or relations of things, yet such as would belong to things even if they were not intuited? Or are space and time such that they belong only to the form of intuition, and therefore to the subjective constitution of the mind, apart from which they could not be ascribed to anything whatsoever?’ (A 23/B 37).
Three views of space and time are on offer here; and it seems clear that Kant regards them as exhaustive. According to the first, the Newtonian (or absolute) view, space and time exist not only independently of being perceived, but independently of any objects (understood as things in themselves) in space or time. This is the view being referred to when it is asked if space and time are real existences. According to the second, Leibnizian (or relational), view, space and time do exist independently of being perceived, but do not exist independently of things in themselves. Space and time are merely the relations holding between things in themselves, which we confusedly perceive by means of sensations in our minds. This is the view that is being referred to when it is asked if space and time are only relations or determinations of things (in themselves), yet such as would belong to things (in themselves) even if they were not intuited.
Kant rejects both these views in favour of a third: viz. that space and time are to be equated with our outer and inner a priori intuitions, respectively. This is the view that he is referring to when he asks if space and time ‘belong . . . only to the subjective constitution of the mind, apart from which they could not be ascribed to anything’. He provides two types of argument for this third view and against the alternative, Newtonian and Leibnizian, views. The first type he calls the ‘Metaphysical Exposition’ of our concepts of space and time; and the second, he calls the ‘Transcendental Exposition’ of these concepts. In dealing with both these expositions, I shall first discuss space and then deal, much more briefly, with time.
The Metaphysical and Transcendental Expositions of space
As regards the Metaphysical Exposition of space, its method is to begin with certain very general thoughts about space (e.g. that each subject thinks that there is only one, and not a multiplicity of, spaces in which he can place objects), and then to show that such thoughts can only be justified if space is a pure (or a priori) intuition. Kant presumably takes it that the proponents of the opposing views of space acknowledge that any acceptable view must accommodate these ideas. I shall follow the text of the B edition, which is divided into four arguments. (The A edition has five arguments; but the third is replaced in the B edition by the Transcendental Exposition.)
Metaphysical Exposition
The first two arguments of the Metaphysical Exposition are designed to show that we have an a priori, and not an empirical, conception of space.
Argument 1: In the opening argument, Kant considers whether our conception of space can have been arrived at from a number of outer experiences, viz. from an empirical consciousness of certain relations holding between the contents of sensations, relations like alongside of, at a distance from, and so on. However, if we had formed our concept of space from outer experiences, it must be possible to think of these experiences independently of thinking of the concept which has allegedly been acquired by means of them. For example, our empirical concept table can be formed by first having sensed instances of the concepts leg, flat top, etc., and acquiring the concept table therefrom. This is possible because the former concepts can be acquired from sensations without presupposing the latter concept. But, Kant contends, we cannot conceivably have built up our concept of space empirically by means of first observing certain relations between outer appearances. For, in order to be empirically conscious of outer appearances as e.g. alongside of or at a distance from each other, we must already have set the manifold of apprehended sensations (out of which the appearances are constituted) together in space.
It is worth remarking that, in the forthcoming Transcendental Analytic, Kant does offer an explanation of why it is that we cannot be empirically conscious of the relations between outer appearances without presupposing the existence of space. This explanation hinges on the argument (which we will examine later) that, in order to be empirically conscious of any relations between appearances, certain synthetic a priori principles must first be applied to the manifold of apprehended sensations or representations. Some of these principles make possible the consciousness of the given manifold as collectively existing in one space, thereby allowing us to have empirical, relational knowledge of outer appearances. On this account, we cannot begin with an empirical consciousness of relations holding between outer appearances and then derive our concept of space therefrom.The very capacity to experience any relations between outer appearances already requires us to have set the manifold of representations constituting the given appearances in one space. It is instructive to compare Argument 1 regarding space with the parallel argument for time (A 30/B 46). In the latter, it is held that time cannot be derived from experiencing the relations of