(_c._) _The Physico-theological proof._—If thus neither conception nor experience can furnish a proof for the divine existence, there still remains a third attempt, viz., to start from a determinate experience, and endeavor to see whether the existence of a supreme being can not be inferred from the arrangement and condition of things in the world. Such is the physico-theological proof, which starts from the evidences of design in nature, and directs its argument as follows: there is evidently design in the universe; this is extraneous to the things of the world, and adheres to them only contingently; there exists therefore a necessary cause of this design which works with wisdom and intelligence; this necessary cause must be the most real being; the most real being has therefore necessary existence.—To this Kant answers: The physico-theological proof is the oldest, clearest, and most conformable to the common reason. But it is not demonstration (apodictic). It infers, from the form of the world, a proportionate and sufficient cause of this form; but in this way we only attain an originator of the form of the world, and not an originator of its matter, a world-builder, and not a world-creator. To help out with this difficulty the cosmological proof is brought in, and the originator of the form becomes conceived as the necessary being lying at the ground of the content. Thus we have an absolute being whose perfection corresponds to that of the world. But in the world there is no absolute perfection; we have therefore only a very perfect being; to get the most perfect, we must revert again to the ontological proof. Thus the teleological proof rests upon the cosmological, while this in turn has its basis in the ontological, and from this circle the metaphysical modes of proof cannot escape.
From these considerations, it would follow that the ideal of a supreme being is nothing other than a regulative principle of the reason, by which it looks upon every connection in the world _as if_ it sprang from an all-sufficient and necessary cause; in order that, in explaining this connection, it may establish the rule of a systematic and necessary unity, it being also true that in this process the reason through a transcendental subreption cannot avoid representing to itself this formal principle as constitutive, and this unity as personal. But in truth this supreme being remains for the simply speculative use of the reason, a mere but faultless ideal, a conception which is the summit and the crown of the whole human knowledge, whose objective reality, though it cannot be proved with apodictic certainty, can just as little be disproved.