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. The really valid argument adduced by Kant for the _a priori_ character of our apprehension of space is based on the nature of geometrical judgements. The universality of our judgements in geometry is not based upon experience, i. e. upon the observation of individual things in space. The necessity of geometrical relations is apprehended directly in virtue of the mind's own apprehending nature. Unfortunately in the present context Kant ignores this argument and substitutes two others, both of which are invalid. 1. "Space is no empirical conception[14] which has been derived from external[15] experiences. For in order that certain sensations may be related to something external to me (that is, to something in a different part of space from that in which I am), in like manner, in order that I may represent them as external to and next to each other, and consequently as not merely different but as in different places, the representation of space must already exist as a foundation. Consequently, the representation of space cannot be borrowed from the relations of external phenomena through experience; but, on the contrary, this external experience is itself first possible only through the said representation."[16] Here Kant is thinking that in order to apprehend, for example, that A is to the right of B we must first apprehend empty space. He concludes that our apprehension of space is _a priori_, because we apprehend empty space _before_ we become aware of the spatial relations of individual objects in it. [14] _Begriff_ (conception) here is to be understood loosely not as something opposed to _Anschauung_ (perception), but as equivalent to the genus of which _Anschauung_ and _Begriff_ are species, i. e. _Vorstellung_, which maybe rendered by 'representation' or 'idea', in the general sense in which these words are sometimes used to include 'thought' and 'perception'. [15] The next sentence shows that 'external' means, not 'produced by something external to the mind', but simply 'spatial'. [16] B. 38, M. 23-4.