Whereas in the first book we were reluctantly forced to declare our own body to be mere representation of the knowing subject, like all the other objects of this world of perception, it has now become clear to us that something in the consciousness of everyone distinguishes the representation of his own body from all others that are in other respects quite like it. This is that the body occurs in consciousness in quite another way, toto genere different, that is denoted by the word will. It is just this double knowledge of our own body which gives us information about that body itself, about its action and movement following on motives, as well as about its suffering through outside impressions, in a word, about what it is, not as representation, but as something over and above this, and hence what it is in itself. We do not have such immediate information about the nature, action, and suffering of any other real objects.
The knowing subject is an individual precisely by reason of this special relation to the one body which, considered apart from this, is for him only a representation like all other representations. But the relation by virtue of which the knowing subject is an individual, subsists for that very reason only between him and one particular representation among all his representations. He is therefore conscious of this particular representation not merely as such, but at the same time in a quite different way, namely as a will. But if he abstracts from that special relation, from that twofold and completely heterogeneous knowledge of one and the same thing, then that one thing, the body, is a representation like all others. Therefore, in order to understand where he is in this matter, the knowing individual must either assume that the distinctive feature of that one representation is to be found merely in the fact that his knowledge stands in this double reference only to that one representation; that only into this one object of perception is an insight in two ways at the same time open to him; and that this is to be explained not by a difference of this object from all others, but only by a difference between the relation of his knowledge to this one object and its relation to all others. Or he must assume that this one object is essentially different from all others; that it alone among all objects is at the same time will and representation, the rest, on the other hand, being mere representation, i.e., mere phantoms. Thus, he must assume that his body is the only real individual in the world, i.e., the only phenomenon of will, and the only immediate object of the subject. That the other objects, considered as mere representations, are like his body, in other words, like this body fill space (itself perhaps existing only as representation), and also, like this body, operate in space—this, I say, is demonstrably certain from the law of causality, which is a priori certain for representations, and admits of no effect without a cause. But apart from the fact that we can infer from the effect only a cause in general, not a similar cause, we are still always in the realm of the mere representation, for which alone the law of causality is valid, and beyond which it can never lead us. But whether the objects known to the individual only as representations are yet, like his own body, phenomena of a will, is, as stated in the previous book, the proper meaning of the question as to the reality of the external world. To deny this is the meaning of theoretical egoism, which in this way regards as phantoms all phenomena outside its own will, just as practical egoism does in a practical respect; thus in it a man regards and treats only his own person as a real person, and all others as mere phantoms. Theoretical egoism, of course, can never be refuted by proofs, yet in philosophy it has never been positively used otherwise than as a sceptical sophism, i.e., for the sake of appearance. As a serious conviction, on the other hand, it could be found only in a madhouse; as such it would then need not so much a refutation as a cure. Therefore we do not go into it any further, but regard it as the last stronghold of scepticism, which is always polemical. Thus our knowledge, bound always to individuality and having its limitation in this very fact, necessarily means that everyone can be only one thing, whereas he can know everything else, and it is this very limitation that really creates the need for philosophy. Therefore we, who for this very reason are endeavouring to extend the limits of our knowledge through philosophy, shall regard this sceptical argument of theoretical egoism, which here confronts us, as a small frontier fortress. Admittedly the fortress is impregnable, but the garrison can never sally forth from it, and therefore we can pass it by and leave it in our rear without danger.
The double knowledge which we have of the nature and action of our own body, and which is given in two completely different ways, has now been clearly brought out. Accordingly, we shall use it further as a key to the inner being of every phenomenon in nature. We shall judge all objects which are not our own body, and therefore are given to our consciousness not in the double way, but only as representations, according to the analogy of this body. We shall therefore assume that as, on the one hand, they are representation, just like our body, and are in this respect homogeneous with it, so on the other hand, if we set aside their existence as the subject’s representation, what still remains over must be, according to its inner nature, the same as what in ourselves we call will. For what other kind of existence or reality could we attribute to the rest of the material world? From what source could we take the elements out of which we construct such a world? Besides the will and the representation, there is absolutely nothing known or conceivable for us. If we wish to attribute the greatest known reality to the material world, which immediately exists only in our representation, then we give it that reality which our own body has for each of us, for to each of us this is the most real of things. But if now we analyse the reality of this body and its actions, then, beyond the fact that it is our representation, we find nothing in it but the will; with this even its reality is exhausted. Therefore we can nowhere find another kind of reality to attribute to the material world. If, therefore, the material world is to be something more than our mere representation, we must say that, besides being the representation, and hence in itself and of its inmost nature, it is what we find immediately in ourselves as will. I say ‘of its inmost nature,’ but we have first of all to get to know more intimately this inner nature of the will, so that we may know how to distinguish from it what belongs not to it itself, but to its phenomenon, which has many grades. Such, for example, is the circumstance of its being accompanied by knowledge, and the determination by motives which is conditioned by this knowledge. As we proceed, we shall see that this belongs not to the inner nature of the will, but merely to its most distinct phenomenon as animal and human being. Therefore, if I say that the force which attracts a stone to the earth is of its nature, in itself, and apart from all representation, will, then no one will attach to this proposition the absurd meaning that the stone moves itself according to a known motive, because it is thus that the will appears in man.56 But we will now prove, establish, and develop to its full extent, clearly and in more detail, what has hitherto been explained provisionally and generally.57