has, in order that we might understand each of them more clearly in isolation, been dissevered in these two books. It may not perhaps be superfluous to elucidate further by an example how the law of causality has meaning only in relation to time and space, and the matter which consists in the union of the two. For it determines the limits in accordance with which the phenomena of the forces of nature divide themselves in the possession of matter, while the original forces of nature, as the immediate objectification of will, which, as a thing in itself, is not subordinated to the principle of sufficient reason, lie outside these forms, within which alone all etiological explanation has validity and meaning, and just on that account can never lead us to the inner reality of nature. For this purpose let us think of some kind of machine constructed according to the laws of mechanics. Iron weights begin the motion by their gravity; copper wheels resist by their rigidity, affect and raise each other and the lever by their impenetrability, and so on. Here gravity, rigidity, and impenetrability are original unexplained forces; mechanics only gives us the condition under which, and the manner in which, they manifest themselves, appear, and govern a definite matter, time, and place. If, now, a strong magnet is made to attract the iron of the weight, and overcome its gravity, the movement of the machine stops, and the matter becomes forthwith the scene of quite a different force of nature—magnetism, of which etiology again gives no further explanation than the condition under which it appears. Or let us suppose that the copper discs of such a machine are laid upon zinc plates, and an acid solution introduced between them. At once the same matter of the machine has become subject to another original force, galvanism, which now governs it according to its own laws, and reveals itself in it through its phenomena; and etiology can again tell us nothing about this force except the conditions under which, and the laws in accordance with which, it manifests itself. Let us now raise the temperature and add pure acid; the whole machine burns; that is to say, once more an entirely different force of nature, chemical energy, asserts at this time and in this place irresistible claims to this particular matter, and reveals itself in it as Idea, as a definite grade of the objectification of will. The calcined metal thus produced now unites with an acid, and a salt is obtained which forms itself into crystals. These are the phenomena of another Idea, which in itself is again quite inexplicable, while the appearance of its phenomena is dependent upon certain conditions which etiology can give us. The crystals dissolve, mix with other materials, and vegetation springs up from them—a new phenomenon of will: and so the same permanent matter may be followed _ad infinitum_, to observe how now this and now that natural