ABSTRACT
As recently as Mach, it seems to have been held that evidence is bound up with such a compulsion. Mach tells us that he gave up solipsism on the ground that he finds himself absolutely compelled to believe in an external world. But Helmholtz, in his Tatsachen der Auβenwelt, says that solipsism is a possible hypothesis and one which cannot be refuted. And Descartes, unlike Mach, found that that compulsion, which one is supposed to feel, could overcome.
