Plato, Timaeus

[71a] concerning what benefits all, both individually and in the mass,—for these reasons they stationed it in that position. And inasmuch as they knew that it would not understand reason, and that, even if it did have some share in the perception of reasons, it would have no natural instinct to pay heed to any of them but would be bewitched for the most part both day and night by images and phantasms,—to guard against this God devised and constructed the form of the liver and placed it in that part's abode; [71b] and He fashioned it dense and smooth and bright and sweet, yet containing bitterness, that the power of thoughts which proceed from the mind, moving in the liver as in a mirror which receives impressions and provides visible images, should frighten this part of the soul; for when the mental power bears down upon it with stern threats, it uses a kindred portion of the liver's bitterness¹ and makes it swiftly suffuse the whole liver, so that it exhibits bilious colors, and by contraction makes it [71c] all wrinkled and rough; moreover, as regards the lobe and passages and gates² of the liver, the first of these it bends back from the straight and compresses, while it blocks the others and closes them up, and thus it produces pains and nausea. On the other hand, when a breath of mildless from the intellect paints on the liver appearances of the opposite kind, and calms down its bitterness by refusing to move or touch the nature opposite to itself, and using upon the liver the sweetness inherent therein [71d] rectifies all its parts so as to make them straight and smooth and free, it causes the part of the soul planted round the liver to be cheerful and serene, so that in the night it passes its time sensibly, being occupied in its slumbers with divination, seeing that in reason and intelligence it has no share.

For they who constructed us, remembering the injunction of their Father, when He enjoined upon them to make the mortal kind [71e] as good as they possibly could, rectified the vile part of us by thus establishing therein the organ of divination, that it might in some degree lay hold on truth. And that God gave unto man's foolishness the gift of divination³ a sufficient token is this: no man achieves true and inspired divination when in his rational mind, but only when the power of his intelligence is fettered in sleep or when it is distraught by disease or by reason of some divine inspiration. But it belongs to a man when in his right mind to recollect and ponder both the things spoken in dream or waking vision by the divining and inspired nature, and all the visionary forms that were seen, and by means of reasoning to discern about them all