XIII. A Rationale of sleep, of yawning, and of dreams .
8 As naturally happens with fire when it is heaped over with chaff, and no breath fans the flame— it neither consumes what lies beside it, nor is entirely quenched, but instead of flame it rises to the air through the chaff in the form of smoke; yet if it should obtain any breath of air, it turns the smoke to flame— in the same way the mind when hidden by the inaction of the senses in sleep is neither able to shine out through them, nor yet is quite extinguished, but has, so to say, a smouldering activity, operating to a certain extent, but unable to operate farther.
9. Again, as a musician, when he touches with the plectrum the slackened strings of a lyre, brings out no orderly melody (for that which is not stretched will not sound), but his hand frequently moves skilfully, bringing the plectrum to the position of the notes so far as place is concerned, yet there is no sound, except that he produces by the vibration of the strings a sort of uncertain and indistinct hum; so in sleep the mechanism of the senses being relaxed, the artist is either quite inactive, if the instrument is completely relaxed by satiety or heaviness; or will act slackly and faintly, if the instrument of the senses does not fully admit of the exercise of its art.
10. For this cause memory is confused, and foreknowledge, though rendered doubtful by uncertain veils, is imaged in shadows of our waking pursuits, and often indicates to us something of what is going to happen: for by its subtlety of nature the mind has some advantage, in ability to behold things, over mere corporeal grossness; yet it cannot make its meaning clear by direct methods, so that the information of the matter in hand should be plain and evident, but its declaration of the future is ambiguous and doubtful,— what those who interpret such things call an “enigma.”
11. So the butler presses the cluster for Pharaoh's cup: so the baker seemed to carry his baskets; each supposing himself in sleep to be engaged in those services with which he was busied when awake: for the images of their customary occupations imprinted on the prescient element of their soul, gave them for a time the power of foretelling, by this sort of prophecy on the part of the mind, what should come to pass.
12. But if Daniel and Joseph and others like them were instructed by Divine power, without any confusion of perception, in the knowledge of things to come, this is nothing to the present statement; for no one would ascribe this to the power of dreams, since he will be constrained as a consequence to suppose that those Divine appearances also which took place in wakefulness were not a miraculous vision but a result of nature brought about spontaneously. As then, while all men are guided by their own minds, there are some few who are deemed worthy of evident Divine communication; so, while the imagination of sleep naturally occurs in a like and equivalent manner for all, some, not all, share by means of their dreams in some more Divine manifestation: but to all the rest even if a foreknowledge of anything does occur as a result of dreams, it occurs in the way we have spoken of.
13. And again, if the Egyptian and the Assyrian king were guided by God to the knowledge of the future, the dispensation wrought by their means is a different thing: for it was necessary that the hidden wisdom of the holy men should be made known, that each of them might not pass his life without profit to the state. For how could Daniel have been known for what he was, if the soothsayers and magicians had not been unequal to the task of discovering the dream? And how could Egypt have been preserved while Joseph was shut up in prison, if his interpretation of the dream had not brought him to notice? Thus we must reckon these cases as exceptional, and not class them with common dreams.
14. But this ordinary seeing of dreams is common to all men, and arises in our fancies in different modes and forms: for either there remain, as we have said, in the reminiscent part of the soul, the echoes of daily occupations; or, as often happens, the constitution of dreams is framed with regard to such and such a condition of the body: for thus the thirsty man seems to be among springs, the man who is in need of food to be at a feast, and the young man in the heat of youthful vigour is beset by fancies corresponding to his passion.
15. I also knew another cause of the fancies of sleep, when attending one of my relations attacked by frenzy; who being annoyed by food being given him in too great quantity for his strength, kept crying out and finding fault with those who were about him for filling intestines with dung and putting them upon him: and when his body was rapidly tending to perspire he blamed those who were with him for having water ready to wet him with as he lay: and he did not cease calling out till the result showed the meaning of these complaints: for all at once a copious sweat broke out over his body, and a relaxation of the bowels explained the weight in the intestines. The same condition then which, while his sober judgment was dulled by disease, his nature underwent, being sympathetically affected by the condition of the body— not being without perception of what was amiss, but being unable clearly to express its pain, by reason of the distraction resulting from the disease— this, probably, if the intelligent principle of the soul were lulled to rest, not from infirmity but by natural sleep, might appear as a dream to one similarly situated, the breaking out of perspiration being expressed by water, and the pain occasioned by the food, by the weight of intestines.
16. This view also is taken by those skilled in medicine, that according to the differences of complaints the visions of dreams appear differently to the patients: that the visions of those of weak stomach are of one kind, those of persons suffering from injury to the cerebral membrane of another, those of persons in fevers of yet another; that those of patients suffering from bilious and from phlegmatic affections are diverse, and those again of plethoric patients, and of patients in wasting disease, are different; whence we may see that the nutritive and vegetative faculty of the soul has in it by commixture some seed of the intelligent element, which is in some sense brought into likeness to the particular state of the body, being adapted in its fancies according to the complaint which has seized upon it.
17. Moreover, most men's dreams are conformed to the state of their character: the brave man's fancies are of one kind, the coward's of another; the wanton man's dreams of one kind, the continent man's of another; the liberal man and the avaricious man are subject to different fancies; while these fancies are nowhere framed by the intellect, but by the less rational disposition of the soul, which forms even in dreams the semblances of those things to which each is accustomed by the practice of his waking hours.
Source: On the Making of Man (New Advent)