According to this view, inasmuch as Nature is only the visible organism of our understanding, Nature can produce nothing but what shows regularity and design, and Nature is compelled to produce that. But if Nature can produce only the regular, and produces it from necessity, it follows that the origin of such regular and design-evincing products must again be capable of being proved necessary in Nature, regarded as self-existent and real, and in the relation of its forces;—that therefore, conversely, the Ideal must arise out of the Real, and admit of explanation from it.
If, now, it is the task of Transcendental Philosophy to subordinate the Real to the Ideal, it is, on the other hand, the task of Natural Philosophy to explain the Ideal by the Real. The two sciences are therefore but one science, whose two problems are distinguished by the opposite directions in which they move; moreover, as the two directions are not only equally possible, but equally necessary, the same necessity attaches to both in the system of knowing.
II.
SCIENTIFIC CHARACTER OF NATURAL PHILOSOPHY.
Natural Philosophy, as the opposite of Transcendental Philosophy, is distinguished from the latter chiefly by the fact that it posits Nature (not, indeed, in so far as it is a product, but in so far as it is at once productive and product) as the self-existent; whence it may be most briefly designated as the Spinozism of Physics. It follows naturally from this that there is no place in this science for idealistic methods of explanation, such as Transcendental Philosophy is fitted to supply, from the circumstance that for it Nature is nothing more than the organ of self-consciousness, and everything in Nature is necessary merely because it is only through the medium of such a Nature that self-consciousness can take place; this mode of explanation, however, is as meaningless in the case of physics, and of our science which occupies the same stand-point with it, as were the old teleological modes of explanation, and the introduction of a universal reference to final causes into the thereby metamorphosed science of Nature. For every idealistic mode of explanation, dragged out of its own proper sphere and applied to the explanation of Nature, degenerates into the most adventurous nonsense, examples of which are well known. The first maxim of all true natural science, viz., to explain everything by the forces of Nature, is therefore accepted in its widest extent in our science, and even extended to that region, at the limit of which all interpretation of Nature has hitherto been accustomed to stop short; for example, to those organic phenomena which seem to pre-suppose an analogy with reason. For, granted that in the actions of animals there really is something which pre-supposes such analogy, on the principle of realism, nothing further would follow than that what we call reason is a mere play of higher and necessarily unknown natural forces. For, inasmuch as all thinking is at last reducible to a producing and reproducing, there is nothing impossible in the thought that the same activity by which Nature reproduces itself anew in each successive phase, is reproductive in thought through the medium of the organism (very much in the same manner in which, through the action and play of light, Nature, which exists independently of it, is created immaterial, and, as it were, for a second time), in which circumstance it is natural that what forms the limit of our intuitive faculty, no longer falls within the sphere of our intuition itself.
III.
NATURAL PHILOSOPHY IS SPECULATIVE PHYSICS.
Our science, as far as we have gone, is thoroughly and completely realistic; it is therefore nothing other than Physics, it is only speculative Physics; in its tendency it is exactly what the systems of the ancient physicists were, and what, in more recent times, the system of the restorer of Epicurean philosophy is, viz., Lesage’s Mechanical Physics, by which the speculative spirit in physics, after a long scientific sleep, has again, for the first time, been awakened. It cannot be shown in detail here (for the proof itself falls within the sphere of our science), that on the mechanical or atomistic basis which has been adopted by Lesage and his most successful predecessors, the idea of speculative physics is incapable of realization. For, inasmuch as the first problem of this science, that of inquiring into the absolute cause of motion (without which Nature is not in itself a finished whole), is absolutely incapable of a mechanical solution, seeing that mechanically motion results only from motion ad infinitum, there remains for the real construction of speculative physics only one way open, viz., the dynamic, which lays down that motion arises not only from motion, but even from rest; that, therefore, there is motion in the rest of Nature, and that all mechanical motion is the merely secondary and derivative motion of that which is solely primitive and original, and which wells forth from the very first factors in the construction of a nature generally (the fundamental forces).
In hereby making clear the points of difference between our undertaking and all those of a similar nature that have hitherto been attempted, we have at the same time shown the difference between speculative physics and so-called empirical physics; a difference which in the main may be reduced to this, that the former occupies itself solely and entirely with the original causes of motion in nature, that is, solely with the dynamical phenomena; the latter, on the contrary, inasmuch as it never reaches a final source of motion in nature, deals only with the secondary motions, and even with the original ones only as mechanical (and therefore likewise capable of mathematical construction). The former, in fact, aims generally at the inner spring-work and what is non-objective in Nature; the latter, on the contrary, only at the surface of Nature, and what is objective, and, so to speak, outside in it.
IV.
ON THE POSSIBILITY OF SPECULATIVE PHYSICS.
Inasmuch as our inquiry is directed not so much upon the phenomena of Nature as upon their final grounds, and our business is not so much to deduce the latter from the former as the former from the latter, our task is simply this: to erect a science of Nature in the strictest sense of the term; and in order to find out whether speculative physics are possible, we must know what belongs to the possibility of a doctrine of Nature viewed as science.
(a) The idea of knowing is here taken in its strictest sense, and then it is easy to see that, in this acceptation of the term, we can be said to know objects only when they are such that we see the principles of their possibility, for without this insight my whole knowledge of an object, e. g. of a machine, with whose construction I am unacquainted, is a mere seeing, that is, a mere conviction of its existence, whereas the inventor of the machine has the most perfect knowledge of it, because he is, as it were, the soul of the work, and because it preëxisted in his head before he exhibited it as a reality.