THE OBJECTIFICATION OF THE WILL. 135
the world, i.e., the only phenomenon of will and the only immediate object of the subject. That other objects, considered merely as ideas, are like his body, that is, like it, fill space (which itself can only be present as idea), and also, like it, are causally active in space, is indeed demonstrably certain from the law of causality which is a priori valid for ideas, and which admits of no effect without a cause; but apart from the fact that we can only reason from an effect to a cause generally, and not to a similar cause, we are still in the sphere of mere ideas, in which alone the law of causality is valid, and beyond which it can never take us. But whether the objects known to the individual only as ideas are yet, like his own body, manifestations of a will, is, as way said in the First Book, the proper meaning of the question as to the reality of the external world. To deny this is theoretical egoism, which on that account regards all phenomena that are outside its own will as phantoms, just as in a practical reference exactly the same thing is done by practical egoism. For in it a man regards and treats himself alone as a person, and all other persons as mere phantoms. Theoretical egoism can never be demonstrably refuted, yet in philosophy it has never been used otherwise than as a sceptical sophism, i.e., a pretence. As a serious conviction, on the other hand, it could only be found in a madhouse, and as such it stands in need of a cure rather than a refutation. We do not therefore combat it any further in this regard, but treat it as merely the last stronghold of scepticism, which is always polemical. Thus our knowledge, which is always bound to individuality and is limited by this circumstance, brings with it the necessity that each of us can only be one, while, on the other hand, each of us can know all; and it is this limitation that creates the need for philosophy. We therefore who, for this very reason, are striving to extend the limits of our knowledge through philosophy, will treat this sceptical argument of theoretical egoism
