(a) The Pure Intuitions (Transcendental Aesthetic).%—­The first part of the Critique of Reason, the Transcendental Aesthetic, lays down the position that space and time are not independent existences, not real beings, and not properties or relations which would belong to things in themselves though they were not intuited, but forms of our intuition, which have their basis in the subjective constitution of our, the human, mind.  If we separate from sensuous intuition all that the understanding thinks in it through its concepts, and all that belongs to sensation, these two forms of intuition remain, which may be termed pure intuitions, since they can be considered apart from all sensation.  As subjective conditions (lying in the nature of the subject) through which alone a thing can become an object of intuition for us, they precede all empirical intuitions or are a priori.

Space and time are neither substantial receptacles which contain all that is real nor orders inhering in things in themselves, but forms of intuition.  Now all our representations are either pure or empirical in their origin, and either intuitive or conceptual in character.  Kant advances four proofs for the position that space and time are not empirical and not concepts, but pure intuitions:  (1) Time is not an empirical concept which has been abstracted from experience.  For the coexistence or succession of phenomena, i.e., their existence at the same time or at different times (from which, as many believe, the representation of time is abstracted), itself presupposes time—­a coexistence or succession is possible only in time.  It is no less false that space is abstracted from the empirical space relations of external phenomena, their existence outside and beside one another, or in different places, for it is impossible to represent relative situation except in space.  Therefore experience does not make space and time possible; but space and time first of all make experience possible, the one outer, the other inner experience.  They are postulates of perception, not abstractions from it. (2) Time is a necessary representation a priori.  We can easily think all phenomena away from it, but we cannot remove time itself in view of phenomena in general; we can think time without phenomena, but not phenomena without time.  The same is true of space in reference to external objects.  Both are conditions of the possibility of phenomena. (3) Time is not a discursive or general concept.  For there is but one time.  And different times do not precede the one time as the constituent parts of which it is made up, but are mere limitations of it; the part is possible only through the whole.  In the same way the various spaces are only parts of one and the same space, and can be thought in it alone.  But a representation which can be given only by a single object is a particular representation or an intuition.  Because, therefore, of the oneness of space and time, the representation