In the argument of the second edition the thesis is again established by reference to the infinity of space. But in all other respects the argument differs from that of the first edition. A general conception, which abstracts out common qualities from a plurality of particulars, contains an infinite number of possible different representations _under_ it; but it cannot be thought as containing an infinite number of representations _in_ it. Space must, however, be thought in this latter manner, for it contains an infinite number of coexisting parts.[448] Since, then, space cannot be a concept, it must be an intuition. The definiteness of this conclusion is somewhat obscured by the further characterisation of the intuition of space as _a priori_, and by the statement that it is the _original_ (_ursprüngliche_) representation which is of this intuitive nature. The first addition must here, again, just as in the fourth argument, be regarded as merely a recapitulation of what has already been established, not a conclusion from the present argument. The introduction of the word ‘original’ seems to be part of Kant’s reply to the objections which had already been made to his admission in the first edition that there is a conception as well as an intuition of space. It is the _original given intuition_ of space which renders such reflective conception possible. The chief difficulty of these proofs arises out of the assertion which they seem to involve that space is given as actually infinite. There are apparently, on this point, two views in Kant, which were retained up to the very last, and which are closely connected with his two representations of space, on the one hand as a _formal intuition_ given in its purity and in its completeness, and on the other hand as the _form of intuition_, which exists only so far as it is constructed, and which is dependent for its content upon given matter. =Third Argument, and Transcendental Exposition of Space.=--The distinction between the metaphysical and the transcendental expositions, introduced in the second edition of the _Critique_,[449] is one which Kant seems to have first made clear to himself in the process of writing the _Prolegomena_.[450] It is a genuine improvement, marking an important distinction. It separates out two comparatively independent lines of argument. The terms in which the distinction is stated are not, however, felicitous. Kant’s reason for adopting the title metaphysical is indicated in the _Prolegomena_:[451] “As concerns the sources of metaphysical cognition, its very concept implies that they cannot be empirical.... For it must not be physical but metaphysical knowledge, _i.e._ knowledge lying beyond experience.... It is therefore _a priori_ knowledge, coming from pure understanding and pure Reason.”