or even when awake:  the Homeric Achilles, beholding Patroclus in a dream, instantly infers that there verily is a shadow, an eidolon, a shadowy consciousness, shadowy presence, which outlasts the death of the body.  To this Epicurus and Lucretius reply, that the belief is caused by fallacious inferences from facts, these facts, appearances beheld in sleep or vision, these spectral faces of the long dead, are caused by ’films peeled off from the surface of objects, which fly to and fro through the air, and do likewise frighten our minds when they present themselves to us awake as well as in sleep, what time we behold strange shapes, and “idols” of the light-bereaved,’ Lucretius expressly advances this doctrine of ‘films’ (an application of the Democritean theory of perception), ’that we may not believe that souls break loose from Acheron, or that shades fly about among the living, or that any part of us is left behind after death’. {341a} Believers in ghosts must have replied that they do not see, in sleep or awake, ‘films’ representing a mouldering corpse, as they ought to do on the Lucretian hypothesis, but the image, or idolon of a living face.  Plutarch says that if philosophers may laugh, these long enduring ‘films,’ from a body perhaps many ages deep in dust, are laughable. {341b} However Lucretius is so wedded to his ‘films’ that he explains a purely fanciful being, like a centaur, by a fortuitous combination of the film of a man with the film of a horse.  A ‘ghost’ then, is, to the mind of Lucretius, merely a casual persistent film of a dead man, composed of atoms very light which can fly at inconceivable speed, and are not arrested by material obstacles.  By parity of reasoning no doubt, if Pythagoras is seen at the same moment in Thurii and Metapontum, only a film of him is beheld at one of these two places.  The Democritean theory of ordinary perception thus becomes the Lucretian theory of dreams and ghosts.  Not that Lucretius denies the existence of a rational soul, in living men, {341c} a portion of it may even leave the body during sleep, and only a spark may be left in the embers of the physical organism.  If even that spark withdraws, death follows, and the soul, no longer warmly housed in the body, ceases to exist.  For the ‘film’ (ghost) is not the soul, and the soul is not the film, whereas savage philosophy identifies the soul with the ghost.  Even Lucretius retains the savage conception of the soul as a thing of rarer matter, a thing partly separable from the body, but that thing is resolved for ever into its elements on the death of the body.  His imaginary ‘film,’ on the other hand, may apparently endure for ages.