We have in nature, according to Kant, a partnership between the irrational and the rational factors. And thereupon he proceeds to argue that we impose laws on nature, understanding thereby that we get hold of reality or objectivity in so far as we are able to imprint the rational element upon the irrational. The positing of the thing _per se_, which has proved a stumbling-block to many, is no more than a confession that we shall never succeed entirely in this business of subjecting the irrational to the rational factor. The thing _per se_ is the X that remains over when the rational function has done its utmost. A thing, a real object, is that which is imprinted with, penetrated with, rationality. The manifolds of space and time, of juxtaposition and sequence are incapable of completely receiving this imprint, that is, of completely responding to our quest for reality, and this their incompetency is expressed in the notion of the thing _per se_. To return to the main question as to the difference between the method by which science proceeds and the reverse method prescribed to ethics, I ask, Why is absolute knowledge of nature impossible? The answer is, Because absolute knowledge would mean the completely rational construction of nature, and this is prevented by the irrational element existing in it. But why has the relative knowledge we possess the character of certainty? Why are we sure of the law of gravitation? Why are we justified in saying that science within certain limits plants her foot on _terra solida_? Because at certain points the sense data do coincide with the rational requirements. There are recurrent phenomena of such a kind, coupled together in such a way, that each is capable of mathematical measurement, and that the sequence of the one after the other can therefore be predicted. Nature might have been arranged quite otherwise. The time spans might have been so long, as to prevent our observing the recurrences. A day-fly cannot observe the periodicity of the earth’s revolution around its axis. The fact however that there is this partial correspondence between human rationality and the unknown nature of things is a bare fact, incapable of explanation.[24] The answer, then, I take it, is: our knowledge of nature is relative, which means incompletely rational, because of the foreign element in nature unamenable to the operation of the rational, the synthetic, function. This relative knowledge is none the less certain, that is, in some sense absolute, because of the partial coincidence of the phenomena of nature and the synthetic processes of the mind.