Thus we see that, with regard to those phenomena which we know only as our ideas, etiology can never give us the desired information that shall carry us beyond this point. For, after all its explanations, they still remain quite strange to us, as mere ideas whose significance we do not understand. The causal connection merely gives us the rule and the relative order of their appearance in space and time, but affords us no further knowledge of that which so appears. Moreover, the law of causality itself has only validity for ideas, for objects of a definite class, and it has meaning only in so far as it presupposes them. Thus, like these objects themselves, it always exists only in relation to a subject, that is, conditionally; and so it is known just as well if we start from the subject, i.e., a priori, as if we start from the object, i.e., a posteriori. Kant indeed has taught us this.
But what now impels us to inquiry is just that we are not satisfied with knowing that we have ideas, that they are such and such, and that they are connected according to certain laws, the general expression of which is the principle of sufficient reason. We wish to know the significance of these ideas; we ask whether this world is merely idea; in which case it would pass by us like an empty dream or a baseless vision, not worth our notice; or whether it is also something else, something more than idea, and if so, what. Thus much is certain, that this something we seek for must be completely and in its whole nature different from the idea; that the forms and laws of the idea must therefore be completely foreign to it; further, that we cannot arrive at it from the idea under the guidance of the laws which merely combine objects, ideas, among themselves, and which are the forms of the principle of sufficient reason.
Thus we see already that we can never arrive at the real nature of things from without. However much we investigate, we can never reach anything but images and names. We are like a man who goes round a castle seeking in vain for an entrance, and sometimes sketching the façades. And yet this is the method that has been followed by all philosophers before me.
§ 18. In fact, the meaning for which we seek of that world which is present to us only as our idea, or the transition from the world as mere idea of the knowing subject to whatever it may be besides this, would never be found if the investigator himself were nothing more than the pure knowing subject (a winged cherub without a body). But he is himself rooted in that world; he finds himself in it as an individual, that is to say, his knowledge, which is the necessary supporter of the whole world as idea, is yet always given through the medium of a body, whose affections are, as we have shown, the starting-point for the understanding in the perception of that world. His body is, for the pure knowing subject, an idea like every other idea, an object among objects. Its movements and actions are so far known to him in precisely the same way as the changes of all other perceived objects, and would be just as strange and incomprehensible to him if their meaning were not explained for him in an entirely different way. Otherwise he would see his actions follow upon given motives with the constancy of a law of nature, just as the changes of other objects follow upon causes, stimuli, or motives. But he would not understand the influence of the motives any more than the connection between every other effect which he sees and its cause. He would then call the inner nature of these manifestations and actions of his body which he did not understand a force, a quality, or a character, as he pleased, but he would have no further insight into it. But all this is not the case; indeed the answer to the riddle is given to the subject of knowledge who appears as an individual, and the answer is will. This and this alone gives him the key to his own existence, reveals to him the significance, shows him the inner mechanism of his being, of his action, of his movements. The body is given in two entirely different ways to the subject of knowledge, who becomes an individual only through his identity with it. It is given as an idea in intelligent perception, as an object among objects and subject to the laws of objects. And it is also given in quite a different way as that which is immediately known to every one, and is signified by the word will. Every true act of his will is also at once and without exception a movement of his body. The act of will and the movement of the body are not two different things objectively known, which the bond of causality unites; they do not stand in the relation of cause and effect; they are one and the same, but they are given in entirely different ways—immediately, and again in perception for the understanding. The action of the body is nothing but the act of the will objectified, i.e., passed into perception. It will appear later that this is true of every movement of the body, not merely those which follow upon motives, but also involuntary movements which follow upon mere stimuli, and, indeed, that the whole body is nothing but objectified will, i.e., will become idea. All this will be proved and made quite clear in the course of this work. In one respect, therefore, I shall call the body the objectivity of will; as in the previous book, and in the essay on the principle of sufficient reason, in accordance with the one-sided point of view intentionally adopted there (that of the idea), I called it the immediate object. Thus in a certain sense we may also say that will is the knowledge a priori of the body, and the body is the knowledge a posteriori of the will. Resolutions of the will which relate to the future are merely deliberations of the reason about what we shall will at a particular time, not real acts of will. Only the carrying out of the resolve stamps it as will, for till then it is never more than an intention that may be changed, and that exists only in the reason in abstracto. It is only in reflection that to will and to act are different; in reality they are one. Every true, genuine, immediate act of will is also, at once and immediately, a visible act of the body. And, corresponding to this, every impression upon the body is also, on the other hand, at once and immediately an impression upon the will. As such it is called pain when it is opposed to the will; gratification or pleasure when it is in accordance with it. The degrees of both are widely different. It is quite wrong, however, to call pain and pleasure ideas, for they are by no means ideas, but immediate affections of the will in its manifestation, the body; compulsory, instantaneous willing or not-willing of the impression which the body sustains. There are only a few impressions of the body which do not touch the will, and it is through these alone that the body is an immediate object of knowledge, for, as perceived by the understanding, it is already an indirect object