a relation between a thing and its image, between matter and thought, since each of these terms possesses, by definition, only that which is lacking to the other? Thus difficulties spring up beneath our feet; and every effort that you make to dispose of one of them does but resolve it into many more. What then do we ask of you? Merely to give up your magician's wand, and to continue along the path on which you first set out. You showed us external images reaching the organs of sense, modifying the nerves, propagating their influence in the brain. Well, follow the process to the end. The movement will pass through the cerebral substance (although not without having tarried there), and will then expand into voluntary action. There you have the whole mechanism of perception. As for perception itself, in so far as it is an image, you are not called upon to retrace its genesis, since you posited it to begin with, and since moreover no other course was open to you. In assuming the brain, in assuming the smallest portion of matter, did you not assume the totality of images? What you have to explain, then, is not how perception arises, but how it is limited, since it should be the image of the whole, and is in fact reduced to the image of that which interests you. But if it differs from the mere image, precisely in that its parts range themselves with reference to a variable centre, its limitation is easy to understand: unlimited de jure, it confines itself de facto
