FORE:Happily the burgomaster intervened, and, as I heard later, got him released.We have seen how Epicurus erected the senses into ultimate arbiters of truth. By so doing, however, he only pushed the old difficulty a step further back. Granting that our perceptions faithfully correspond to certain external images, how can we be sure that these images are themselves copies of a solid and permanent reality? And how are we to determine the validity of general notions representing not some single object but entire classes of objects? The second question may be most conveniently answered first. Epicurus holds that perception is only a finer sort of sensation. General notions are material images of a very delicate texture formed, apparently, on the principle of composition-photographs by the coalescence of many individual images thrown off from objects possessing a greater or less degree of resemblance to one another.186 Thought is produced by the contact of such images with the soul, itself, it will be remembered, a material substance.