That there is a sun apart from my sensation of it is an inference. The fact that I have a brain, though I cannot see it, is likewise an inference. We know about these things only in theory, and not by immediate experience. But this “external” world of theoretical objects is, apparently, just as much a unity as the “internal” world of experience. From experience I infer that it exists. And because experience is a unity—I am my sensations—I must likewise infer that this theoretical universe is a unity, that my body and the world form a single process.
