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Democritus says that dreams are formed by the illapse of adventitious representations. Strato, that the irrational part of the soul in sleep becoming more sensible is moved by the rational part of it. Herophilus, that dreams which are caused by divine instinct have a necessary cause; but dreams which have their origin from a natural cause arise from the soul's forming within itself the images of those things which are convenient for it, and which will happen; those dreams which are of a constitution mixed of both these have their origin from the fortuitous appulse of images, as when we see those things which please us; thus it happens many times to those persons who in their sleep imagine they embrace their mistresses.