The refinements which the Chinese bring to physical punishment are nothing but a very clear indication of insensibility. That which agonizes a European makes a yellow man smile. But there are, among men of the same social group, numerous degrees of sensibility. Pain, like pleasure, is a representation. The formula has been extended to groups. A people is what it believes itself to be, very much more than what it actually is. Most social disorders are merely collective representations. But it is difficult to explain idealism by an examination of the facts of sensibility. They are too well known, too generally admitted, to support a philosophic construction. A point of departure more extraordinary and less easy to understand is needed. The phenomenon of vision is generally employed in this connection. It seems simple, but, when analyzed, it is exceedingly mysterious. Seeing is the most natural thing in the world. Yet, what do we see, when we see a tree? A tree, to be sure, but not the tree itself. What enters us, as object perceived, is not the tree as tree, but the tree as image. What is the image worth? Is it exact? So it may be supposed, since it is sensibly the same for the various persons who perceive it, and since divergences of appreciation begin only when there come into play judgments conditioned by sentiment or interest. This supposed exactitude is, in any case, very relative. An image is an image, a photograph, and it differs from the reality-tree (pure hypothesis) as much as a round, long, branching, leafy object differs from a graphic representation, without thickness. It is true that tactile sensation, or its memory, comes then to our aid, adding to the tenuousness of the visual image the idea of consistence, of resistance, without which we have difficulty in conceiving matter. We can then--and thanks also to our observation of the opposing play of light and shade--give this vain image its true position in space. But however complete and concordant may be the actions of our senses, when it is a question of knowing an object--even when, as in sexual love, the six senses, including the genital sense, come into play simultaneously--it is none the less the fact that the object known remains exterior to ourselves. Besides, this qualification "known" is little appropriate to the object perceived, since it has an interior face, inaccessible at first glance to our senses. If we are dealing with a living being--and all the more if this being be intelligent and complex--we must exercise all sorts of faculties and devote ourselves to minute analyses in order to arrive, even then, at a knowledge that is very nearly illusory.