outer objects but only their inner copies. There must be two external worlds, the actual world in space and the apparently real but merely subjective world of each separate observer.[1] Such an argument is, as Avenarius contends,[2] obviously false. It rests on the assumption that the objects which I immediately experience as outside the body of another person are the real objects which that other person apprehends only indirectly through mental copies. That is to say, on a realistic interpretation of my own experience I base an idealistic interpretation of the experience of others. This contradiction becomes explicit when I am compelled to extend the conclusion thus reached to my own experience, for in so doing I destroy the premiss upon which the whole argument rests.
Now I have not the least intention of seeking to defend such a form of argument. Also, I do not question that in all subjectivist thinking a perpetual alternation between the realistic and the idealistic attitudes is inevitable. In one form or another the realistic assumption is always tacitly made; and that assumption undoubtedly has its origin in the realistic attitude which we spontaneously take up towards the sensible world of immediate experience. Avenarius, in tracing the presence of this self-contradictory assumption through all the various forms of subjective idealism, has rendered a genuine service to philosophy. What I call in question is his assertion that subjective idealism not only logically implies, but finds its originating cause in, this false inference. It is to be observed that Avenarius has given no ground for the assumed necessity of the introjectionist argument save only the spatial externality of objects to the bodies of those who perceive them; and that seems to me insufficient to account for desertion of the realistic attitude of ordinary consciousness. No one at the standpoint of pure experience can fail to observe this spatial externality, and, so far from finding it a stumbling-block and a source of problems, must surely recognise it as necessary for the very purpose of knowledge. We cannot in looking through a window see an external landscape unless the landscape actually exists outside the window, and just as little can we in looking out upon the external world through the eyes—and that is what primitive and unreflective man conceives himself as doing—see that world unless it is actually there outside the eyes. Avenarius insists that the realistic attitude of pure experience is a perfectly satisfac-
