The formal in Nature, in this narrower signification, is then the regularity of all the objects of experience, and in so far as they are known a priori, their necessary regularity. But it has been just demonstrated that the laws of Nature can never be known a priori in objects, in so far as they are considered not as the objects of a possible experience but as things in themselves. We are not here concerned with things in themselves (the qualities of which we put on one side), but merely with things as the objects of a possible experience, and the sum-total of which is properly what we call Nature. And I now ask, whether, if the question be as to the possibility of a cognition of Nature a priori, it would be better to formulate the problem, as follows: How is it possible to cognise a priori the necessary regularity of things as objects of experience? or, How is the necessary regularity of experience itself in respect of all its objects, generally [possible to be cognised a priori]?
Seen in its true light, the solution of the problem, whether presented in the one or in the other form, in respect of the pure cognition of Nature (which constitutes the real point of the question) is in the end altogether the same. For the subjective laws under which alone an experiential cognition of things is possible, are valid also of those things as objects of a possible experience (though not indeed as things in themselves; but the latter we are not here consider- ing). It is quite the same, then, whether I say: Without the law—that on an event being perceived, it must invariably be referred to something preceding it, upon which it follows according to a universal rule—a judgment of perception can never avail as experience; or whether I express myself thus: Everything that experience teaches us, happens, must have a cause.
It is, however, advisable to choose the first formula. For as we can have a knowledge a priori and before all given objects, of those conditions under which alone an experience in respect of them is possible, but never of what laws, they, without reference, to a possible experience, are subordinated to, in themselves; we shall not be able to study the nature of things a priori, otherwise than by investigating the conditions and universal (although subjective) laws, under which such a knowledge is alone possible (in respect of mere form), as experience, and in accordance therewith deter- mine the possibility of things as objects of experience. Were I to choose the second mode of expression and seek the conditions aprioriunder which Nature is possible as an object of experience, I should easily be led into misunderstand- ing, and fancy I had to explain Nature as a thing in itself, and I should then be fruitlessly involved in endless endeavours to seek laws for things of which nothing is given me.
We shall here, therefore, be simply concerned with experience, and the universal and a priori given conditions of its possibility, and thence determine Nature as the complete object of all possible experience. I think it will be understood, that I do not refer to the rules for the observation of a nature already given, which presuppose experience, or how through experience we can arrive at the laws of Nature, for these would not then be laws a priori, and would give no pure science of Nature; but how the conditions aprioriof the possibility of experience are at the same time the sources from which all the universal laws of Nature must be derived.