1. THE TRANSCENDENTAL ÆSTHETICS.—To anticipate at once the answer, we may say that the apriori principles of our knowledge through the sense, the original forms of sensuous intuition, are space and time. Space is the form of the external sense, by means of which objects are given to us as existing outside of ourselves separately and conjointly; time is the form of the inner sense, by means of which the circumstances of our own soul-life become objects to our consciousness. If we abstract every thing belonging to the matter of our sensations, space remains as the universal form in which all the materials of the external sense must be arranged. If we abstract every thing which belongs to the matter of our inner sense, time remains as the form which the movement of the mind had filled. Space and time are the highest forms of the outer and inner sense. That these forms lie apriori in the human mind, Kant proves, first, directly from the nature of these conceptions themselves; and, secondly, indirectly by showing that without apriori presupposing these conceptions, it were not possible to have any certain science of undoubted validity. The first of these he calls the _metaphysical_, and the second the _transcendental discussion_.
(1.) In the _metaphysical discussion_ it is to be shown, (_a_) that space and time are apriori given, (_b_) that these notions belong to the sensory (æsthetics) and not to the understanding (logic), _i. e._ that they are intuitions and not conceptions, (_a_) That space and time are apriori is clear from the fact that every experience, before it can be, must presuppose already a space and time. I perceive something as external to me; but this external presupposes space. Again, I have two sensations at the same time and successively; this presupposes time, (_b_) Space and time, however, are by no means conceptions, but forms of intuition, or intuitions themselves. For in every universal conception the individual is comprehended under it, and is not a part of it; but in space and time, all individual spaces and times are parts of and contained within the universal space and the universal time.