Timaeus

but when some greater motions are still left behind, according to their nature and the positions they occupy such and so great are the images they produce, which images are copied within and are remembered by the sleepers when they awake out of the dream. And it is no longer difficult to perceive the truth about the formation of images in mirrors and in bright and smooth surfaces of every kind. It is from the combination with each other of the inner and the outer fires, every time that they unite on the smooth surface and are variously deflected, that all such reflections necessarily result, owing to the fire of the reflected face coalescing with the fire of the vision on the smooth and bright surface. And left appears as right, because contact takes place between opposite portions of the visual stream and opposite portions of the object, contrary to the regular mode of collision. Contrariwise, right appears as right and left as left whenever the fire changes sides on coalescing with the object wherewith it coalesces; and this occurs whenever the smooth surface of the mirrors, being elevated on this side and on that, repels the right portion of the visual stream to the left and the left to the right. And when this same mirror is turned lengthwise to the face it makes the whole face appear upside down, since it repels the bottom of the ray to the top, and conversely the top to the bottom. Now all these are among the auxiliary Causes which God employs as his ministers in perfecting, so far as possible, the Form of the Most Good; but by the most of men they are supposed to be not auxiliary but primary causes of all things—cooling and heating, solidifying and dissolving, and producing all such effects. Yet they are incapable of possessing reason and thought for any purpose. For, as we must affirm, the one and only existing thing which has the property of acquiring thought is Soul; and Soul is invisible, whereas fire and water and earth and air are all visible bodies; and the lover of thought and knowledge must needs pursue first the causes which belong to the Intelligent Nature, and put second all such as are of the class of things which are moved by others, and themselves, in turn, move others because they cannot help it. And we also must act likewise. We must declare both kinds of Causes, but keep distinct those which, with the aid of thought, are artificers of things fair and good, and all those which are devoid of intelligence and produce always accidental and irregular effects.