This adoption of the Newtonian view of space in 1768 was an important step forward in the development of Kant’s teaching, but could not, in view of the many metaphysical difficulties to which it leads, be permanently retained; and in the immediately following year—a year which, as he tells us,[629] “gave great light”—he achieved the final synthesis which enabled him to combine all that he felt to be essential in the opposing views. Though space is an absolute and preconditioning source of differences which are not conceptually resolvable, it is a merely subjective form of our sensibility.
Now it is significant that when Kant expounds this view in the Dissertation of 1770, the argument from incongruous counterparts is no longer employed to establish the absolute and pre-conditioning character of space, but only to prove that it is a pure non-conceptual intuition.
“Which things in a given space lie towards one side, and which lie towards the other, cannot by any intellectual penetration be discursively described or reduced to intellectual marks. For in solids that are completely similar and equal, but incongruent, such as the right and the left hand (conceived solely in terms of their extension), or spherical triangles from two opposite hemispheres, there is a diversity which renders impossible the coincidence of their spatial boundaries. This holds true, even though they can be substituted for one another in all those respects which can be expressed in marks that are capable of being made intelligible to the mind through speech. It is therefore evident that the diversity, that is, the incongruity, can only be apprehended by some species of pure intuition.”[630]
There is no mention of this argument in the first edition of the Critique, and when it reappears in the Prolegomena it is interpreted in the light of an additional premiss, and is made to yield a very different conclusion from that drawn in the Dissertation, and a directly opposite conclusion from that drawn in 1768. Instead of being employed to establish either the intuitive character of space or its absolute existence, it is cited as evidence in proof of its subjectivity. As in 1768, it is spoken of as strange and paradoxical, and many of the previous illustrations are used. The paradox consists in the fact that bodies and spherical figures, conceptually considered, can be absolutely identical, and yet for intuition remain diverse. This paradox, Kant now maintains[631] in opposition to his 1768 argument, proves that such bodies and the space within which they fall are not independent existences. For were they things in themselves, they would be adequately cognisable through the pure understanding, and could not therefore conflict with its demands. Being conceptually identical, they would necessarily be congruent in every respect. But if space is merely the form of sensibility, the fact that in space the part is only possible through the whole will apply to everything in it, and so will generate a fundamental difference between conception and intuition.[632] Things in themselves are, as such, unconditioned, and cannot, therefore, be dependent upon anything beyond themselves. The objects of intuition, in order to be possible, must be merely ideal.
Now the new premiss which differentiates this argument from that of 1768, and which brings Kant to so opposite a conclusion, is one which is entirely out of harmony with the teaching of the Critique. In this section of the Prolegomena Kant has unconsciously reverted to the dogmatic standpoint of the Dissertation, and is interpreting understanding in the illegitimate manner which he so explicitly denounces in the section on Amphiboly.
“The mistake ... lies in employing the understanding contrary to its vocation transcendentally [i.e. transcendently] and in making objects, i.e. possible intuitions, conform to concepts, not concepts to possible intuitions, on which alone their objective validity rests.”[633]
The question why no mention of this argument is made in the second edition of the Critique is therefore answered. Kant had meantime, in the interval between 1783 and 1787,[634] become aware of the inconsistency of the position. So far from being a paradox, this assumed conflict rests upon a false view of the function of the understanding.[635] The relevant facts may serve to confirm the view of space as an intuition in which the whole precedes the parts;[636] but they can afford no evidence either of its absoluteness or of its ideality. In 1768 they seem to Kant to prove its absoluteness, only because the other alternative has not yet occurred to him. In 1783 they seem to him to prove its ideality, only because he has not yet completely succeeded in emancipating his thinking from the dogmatic rationalism of the Dissertation.
As already noted,[637] Kant’s reason for here asserting that space is intuitive in nature, namely, that in it the parts are conditioned by the whole, is also his reason for elsewhere describing it as an Idea of Reason. The further implication of the argument of the Prolegomena, that in the noumenal sphere the whole is made possible only by its unconditioned parts, raises questions the discussion of which must be deferred. The problem recurs in the Dialectic in connection with Kant’s definition of the Idea of the unconditioned. In the Ideas of Reason Kant comes to recognise the existence of concepts which do not conform to the reflective type analysed by the traditional logic, and to perceive that these Ideas can yield a deeper insight than any possible to the discursive understanding. The above rationalistic assumption must not, therefore, pass unchallenged. It may be that in the noumenal sphere all partial realities are conditioned by an unconditioned whole.
Concluding Paragraph.[638]—The wording of this paragraph is in keeping with the increased emphasis which in the Introduction to the second edition is given to the problem, how a priori synthetic judgments are possible. Kant characteristically fails to distinguish between the problems of pure and applied mathematics, with resulting inconsecutiveness in his argumentation.