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.____________________