Now, it would certainly be impossible to obtain a glance into the internal construction of Nature, if an invasion of Nature were not possible through freedom. It is true that Nature acts openly and freely; its acts however are never isolated, but performed under a concurrence of a host of causes, which must first be excluded if we are to obtain a pure result. Nature must therefore be compelled to act under certain definite conditions, which either do not exist in it at all, or else exist only as modified by others.—Such an invasion of Nature we call an experiment. Every experiment is a question put to Nature, to which she is compelled to give a reply. But every question contains an implicit à priori judgment; every experiment that is an experiment, is a prophecy; experimenting itself is a production of phenomena. The first step, therefore, towards science, at least in the domain of physics, is taken when we ourselves begin to produce the objects of that science.
(b) We know only the self-produced; knowing, therefore, in the strictest acceptation of the term, is a pure knowing à priori. Construction by means of experiment, is, after all, an absolute self-production of the phenomena. There is no question but that much in the science of Nature may be known comparatively à priori; as, for example, in the theory of the phenomena of electricity, magnetism, and even light. There is such a simple law recurring in every phenomenon that the results of every experiment may be told beforehand; here my knowing follows immediately from a known law, without the intervention of any particular experience. But whence then does the law itself come to me? The assertion is, that all phenomena are correlated in one absolute and necessary law, from which they can all be deduced; in short, that in natural science all that we know, we know absolutely à priori. Now, that experiment never leads to such a knowing, is plainly manifest, from the fact that it can never get beyond the forces of Nature, of which itself makes use as means.
As the final causes of natural phenomena are themselves not phenomenal, we must either give up all attempt ever to arrive at a knowledge of them, or else we must altogether put them into Nature, endow Nature with them. But now, that which we put into Nature has no other value than that of a pre-supposition (hypothesis), and the science founded thereon must be equally hypothetical with the principle itself. This it would be possible to avoid only in one case, viz., if that pre-supposition itself were involuntary, and as necessary as Nature itself. Assuming, for example, what must be assumed, that the sum of phenomena is not a mere world, but of necessity a Nature—that is, that this whole is not merely a product, but at the same time productive, it follows that in this whole we can never arrive at absolute identity, inasmuch as this would bring about an absolute transition of Nature, in as far as it is productive, into Nature as product, that is, it would produce absolute rest; such wavering of Nature, therefore, between productivity and product, will, of necessity, appear as a universal duplicity of principles, whereby Nature is maintained in continual activity, and prevented from exhausting itself in its product; and universal duality as the principle of explanation of Nature will be as necessary as the idea of Nature itself.
This absolute hypothesis must carry its necessity within itself, but it must, besides this, be brought to empiric proof; for, inasmuch as all the phenomena of Nature cannot be deduced from this hypothesis as long as there is in the whole system of Nature a single phenomenon which is not necessary according to that principle, or which contradicts it, the hypothesis is thereby at once shown to be false, and from that moment ceases to have validity as an hypothesis.
By this deduction of all natural phenomena from an absolute hypothesis, our knowing is changed into a construction of Nature itself, that is, into a science of Nature à priori. If, therefore, such deduction itself is possible, a thing which can be proved only by the fact, then also a doctrine of Nature is possible as a science of Nature; a system of purely speculative physics is possible, which was the point to be proved.
Remark.—There would be no necessity for this remark, if the confusion which still prevails in regard to ideas perspicuous enough in themselves did not render some explanation with regard to them requisite.
The assertion that natural science must be able to deduce all its principles à priori, is in a measure understood to mean that natural science must dispense with all experience, and, without any intervention of experience, be able to spin all its principles out of itself—an affirmation so absurd that the very objections to it deserve pity. Not only do we know this or that through experience, but we originally know nothing at all except through experience, and by means of experience, and in this sense the whole of our knowledge consists of the data of experience. These data become à priori principles when we become conscious of them as necessary, and thus every datum, be its import what it may, may be raised to that dignity, inasmuch as the distinction between à priori and à posteriori data is not at all, as many people may have imagined, one originally cleaving to the data themselves, but is a distinction made solely with respect to our knowing, and the kind of our knowledge of these data, so that every datum which is merely historical for me—i. e. a datum of experience—becomes, notwithstanding, an à priori principle as soon as I arrive, whether directly or indirectly, at insight into its internal necessity. Now, however, it must in all cases be possible to recognize every natural phenomenon as absolutely necessary; for, if there is no chance in nature at all, there can likewise be no original phenomenon of Nature fortuitous; on the contrary, for the very reason that Nature is a system, there must be a necessary connection for everything that happens or comes to pass in it, in some principle embracing the whole of Nature. Insight into this internal necessity of all natural phenomena becomes, of course, still more complete, as soon as we reflect that there is no real system which is not, at the same time, an organic whole. For if, in an organic whole, all things mutually bear and support each other, then this organization must have existed as a whole previous to its parts—the whole could not have arisen from the parts, but the parts must have arisen out of the whole. It is not, therefore, WE KNOW Nature, but Nature IS, à priori, that is, everything individual in it is predetermined by the whole or by the idea of a Nature generally. But if Nature is à priori, then it must be possible to recognize it as something that is à priori, and this is really the meaning of our affirmation.
Such a science, like every other, does not deal with the hypothetical, or the merely probable, but depends upon the evident and the certain. Now, we may indeed be quite certain that every natural phenomenon, through whatever number of intermediate links, stands in connection with the last conditions of a Nature; the intermediate links themselves, however, may be unknown to us, and still lying hidden in the depths of Nature. To find out these links is the work of experimental research. Speculative physics have nothing to do but to show the need of these intermediate links;[[18]] but as every new discovery throws us back upon a new ignorance, and while one knot is being loosed a new one is being tied, it is conceivable that the complete discovery of all the intermediate links in the chain of Nature, and therefore also our science itself, is an infinite task. Nothing, however, has more impeded the infinite progress of this science than the arbitrariness of the fictions by which the want of profound insight was so long doomed to be concealed. This fragmentary nature of our knowledge becomes apparent only when we separate what is merely hypothetical from the pure out-come of science, and thereupon set out to collect the fragments of the great whole of Nature again into a system. It is, therefore, conceivable that speculative physics (the soul of real experiment) has, in all time, been the mother of all great discoveries in Nature.
V.
OF A SYSTEM OF SPECULATIVE PHYSICS GENERALLY.
Hitherto the idea of speculative physics has been deduced and developed; it is another business to show how this idea must be realized and actually carried out.