What, then, was to be done? Descartes's rivals and successors attempted several solutions, which it would be too long to examine here. They dissatisfied Leibniz and they have certainly no less dissatisfied posterity. It will be enough for us here to consider what Leibniz did. He admitted, to begin with, the psychological fact. The unity of consciousness is the representation of a plurality--the plurality of the members, and through them the plurality of the world. Here, surely, was the very principle the new philosophy needed for the reconciliation of substantial unity with mechanical plurality of parts. For it is directly evident to us that consciousness focuses the plurality of environing things in a unity of representation. This is no philosophical theory, it is a simple fact. Our body, then, as a physical system is a mechanical plurality; as focused in consciousness it is a unity of 'idea'. Very well: but we have not got far yet. For the old difficulty still remains--it is purely arbitrary, after all, that a unitary consciousness should be attached to, and represent, a mechanical collection of things which happen to interact in a sort of pattern. If there is a consciousness attached to human bodies, then why not to systems of clockwork? If the body is _represented_ as unity, it must surely be because it _is_ unity, as the old philosophy had held. But how can we reintroduce unity into the body without reintroducing substantial form, and destroying the mechanistical plurality which the new science demanded? It is at this point that Leibniz produces the speculative postulate of his system. Why not reverse the relation, and make the members represent the mind as the mind represents the members? For then the unity of person represented in the mind will become something actual in the members also.