 At this point in his argumentation, Schopenhauer has established only that among his many ideas, or representations, only one of them (viz., the [complex] representation of his body) has this special double-aspected quality. When he perceives the moon or a mountain, he does not under ordinary circumstances have any direct access to the metaphysical inside of such objects; they remain as representations that reveal to him only their objective side. Schopenhauer asks, though, how he might understand the world as an integrated whole, or how he might render his entire field of perception the most comprehensible, for as things stand, he can directly experience the inside of one of his representations, but of no others. To answer this question, he uses the double-knowledge of his own body as the key to the inner being of every other natural phenomenon: he regards – as if he were trying to make the notion of universal empathy theoretically possible – every object in the world as being metaphysically double-aspected, and as having an inside or inner aspect of its own, just as his consciousness is the inner aspect of his own body. This is his rationale for rejecting Descartes’s causal interactionism, where thinking substance is said to cause changes in an independent material substance and vice-versa.