1 · We must, in the next place, investigate the subject of the dream, and first inquire to which of the faculties of the soul it presents itself, i.e. whether the [458b1] affection is one which pertains to the faculty of thought or to that of sense-perception; for these are the only faculties within us by which we acquire knowledge.
If, then, the exercise of the faculty of sight is seeing, that of the auditory faculty, hearing, and, in general that of the faculty of sense-perception, perceiving; and if there are some perceptions common to the senses, such as figure, magnitude, [5] motion, &c, while there are others, as colour, sound, taste, which are special; and further, if all creatures, when the eyes are closed in sleep, are unable to see, and the analogous statement is true of the other senses, it is clear that we perceive nothing when asleep; we may conclude that it is not by sense-perception we perceive a dream.
But neither is it by opinion that we do so. For we not only assert, e.g., that some [10] object approaching is a man or a horse, but that the object is white or beautiful, points on which opinion without sense-perception would say nothing either truly or falsely. It is, however, a fact that the soul makes such assertions in sleep. We seem to see equally well that the approaching figure is a man, and that it is white. Again, we think of something else, over and above the dream, just as we do in waking [15] moments when we perceive something; for we often also reason about that which we perceive. So, too, in sleep we sometimes have thoughts other than the images. This would be manifest to any one who should attend and try, immediately on arising from sleep, to remember. There are cases of persons who have seen such dreams, [20] those, for example, who believe themselves to be mentally arranging a given list of subjects according to the mnemonic rule. They frequently find themselves to be mentally putting into its place some other image apart from the dream. Hence it is plain that not every image in sleep is a dream, and that the thinking which we perform then is due to an exercise of the faculty of opinion. [25]
So much at least is plain on all these points, viz. that the faculty by which, in waking hours, we are subject to illusion when affected by disease, is identical with that which produces illusory effects in sleep. So, even when persons are in excellent health, and know the facts of the case perfectly well, the sun, nevertheless, appears [30] to them to be only a foot wide. Now, whether the imaginative faculty of the soul be identical with, or different from, the faculty of sense-perception, in either case the thing does not occur without our seeing or perceiving something. Even to see wrongly or to hear wrongly can happen only to one who sees or hears something real, though not exactly what he supposes. But we have assumed that in sleep one [459a1] neither sees, nor hears, nor exercises any sense whatever. Perhaps we may regard it as true that the dreamer sees nothing, yet as false that his faculty of sense-perception is unaffected, the fact being that the sense of seeing and the other senses may possibly be then in a certain way affected, while each of these affections, as [5] when he is awake, gives its impulse in a certain manner to his faculty of sense, though not in the same manner as when he is awake. Sometimes, too, opinion says, just as to those who are awake, that it is false; at other times it is inhibited, and follows the image.
It is plain therefore that this affection, which we name dreaming, is no exercise of opinion or thought but yet is not an affection of the faculty of perception in the [10] simple sense. If it were the latter it would be possible to hear and see in the simple sense.
How then, and in what manner, it takes place, is what we have to examine. Let us assume, what is indeed clear enough, that the affection pertains to sense-perception as surely as sleep itself does. For sleep does not pertain to one organ in animals and dreaming to another; both pertain to the same organ.
[15] But since we have, in our work on the soul, treated of imagination, and the faculty of imagination is identical with that of sense-perception, though the being of a faculty of imagination is different from that of a faculty of sense-perception; and since imagination is the movement set up by a sensory faculty when actually discharging its function, while a dream appears to be an image (for which occurs in [20] sleep—whether simply or in some particular way—is what we call a dream): it manifestly follows that dreaming is an activity of the faculty of sense-perception, but belongs to this faculty qua imaginative.
2 · We can best consider the nature of the dream and the manner in which it originates by regarding it in the light of the circumstances attending sleep. The [25] objects of sense-perception corresponding to each sensory organ produce sense-perception in us, and the affection due to their operation is present in the organs of sense not only when the perceptions are actualized, but even when they have departed.
What happens in these cases may be compared with what happens in the case of projectiles moving in space. For in the case of these the movement continues even [30] when that which set up the movement is no longer in contact. For that which set them in motion moved a certain portion of air, and this, in turn, being moved excites motion in another portion; and so it is in this way that the bodies, whether in air or in liquids, continue moving, until they come to a standstill.
[459b1] This we must likewise assume to happen in the case of qualitative change; for that part which has been heated by something hot, heats the part next to it, and this propagates the affection onwards to the starting-point. This must therefore happen in sense-perception, since actual perceiving is a qualitative change. This explains why the affection continues in the sensory organs, both in their deeper and in their more superficial parts, not merely while they are actually engaged in perceiving, [5] but even after they have ceased to do so. That they do this, indeed, is obvious in cases where we continue for some time engaged in a particular form of perception; for then, when we shift the scene of our perceptive activity, the previous affection remains; for instance, when we have turned our gaze from sunlight into darkness. For the result of this is that one sees nothing, owing to the motion excited by the [10] light still subsisting in our eyes. Also, when we have looked for a long while at one colour, e.g. at white or green, that to which we next transfer our gaze appears to be of the same colour. Again if, after having looked at the sun or some other brilliant object, we close the eyes, then, if we watch carefully, it appears in a right line with the direction of vision (whatever this may be), at first its own colour; then it changes [15] to crimson, next to purple, until it becomes black and disappears. And also when persons turn away from looking at objects in motion, e.g. rivers, and especially those which flow very rapidly, things really at rest are then seen as moving; and persons [20] become deaf after hearing loud noises, and after smelling very strong odours their power of smelling is impaired; and similarly in other cases. These phenomena manifestly take place in the way above described.
That the sensory organs are acutely sensitive to even a slight qualitative difference is shown by what happens in the case of mirrors; a subject to which, even [25] taking it independently, one might devote close consideration and inquiry. At the same time it becomes plain from them that as the eye is affected, so also it produces a certain effect. For in the case of very bright mirrors, when women during their menstrual periods look into the mirror, the surface of the mirror becomes a sort of bloodshot cloud; and if the mirror is new, it is not easy to wipe off such a stain, while if it is old it is easier. The cause is, as we said, that the eye is not only affected by the [460a1] air but also has an effect upon it and moves it—as bright objects do (for the eye is a bright object and has colour). Now it is reasonable that the eyes, like any other part whatsoever, should be affected during the menstrual period; for they are veined by [5] nature. That is why, when the menstrual discharges occur because of a disturbance and bloody inflammation, the change in the eyes is not evident to us although it is present (for the nature of the discharges is the same as that of semen); and the air is moved by them, and has a certain effect on the air on the surface of the mirror which is continuous with it, i.e. it makes that air affected in the same way that it is [10] itself; and the air on the mirror affects the surface of the mirror.
As in the case of clothes, the purest mirrors are most quickly stained; for a pure mirror shows accurately whatever it receives, and the purest shows the smallest movements. The bronze, because it is smooth, perceives best any touch at all (one [15] should think of the touch of the air as a sort of rubbing—like a wiping or a washing), and because it is pure the touch, however slight it may be, becomes apparent in it. The reason why the stain does not leave new mirrors quickly is their [20] purity and smoothness; for in their case it penetrates both in depth and all over—in depth because of their purity, all over because of their smoothness. The stain does not remain on old mirrors because it does not penetrate in the same way but more superficially.
It is plain from this that motion is set up even by small differences, and that [25] perception is swift, and that the organ which perceives colour is not only affected but also has an effect in return. Further evidence to the same point is afforded by what takes place in wines, and in the manufacture of unguents. For both oil, when prepared, and wine become rapidly infected by the odours of the things near them; [30] they not only acquire the odours of the things thrown into or mixed with them, but also those of the things which are placed, or which grow, near the vessels containing them.
[460b1] In order to answer our original question, let us now, therefore, assume one proposition, which is clear from what precedes, viz. that even when the external object of perception has departed, the impressions it has made persist, and are themselves objects of perception; and let us assume, besides, that we are easily deceived respecting the operations of sense-perception when we are excited by emotions, and different persons according to their different emotions; for example, [5] the coward when excited by fear, the amorous person by amorous desire; so that, with but little resemblance to go upon, the former thinks he sees his foes approaching, the latter, that he sees the object of his desire; and the more deeply one is under the influence of the emotion, the less similarity is required to give rise to these impressions. Thus, too, both in fits of anger, and also in all states of appetite, [10] all men become easily deceived, and more so the more their emotions are excited. This is the reason too why persons in the delirium of fever sometimes think they see animals on their chamber walls because of the faint resemblance to animals of the markings thereon when put together in patterns; and this sometimes corresponds with the emotional states of the sufferers, in such a way that, if the latter be not very [15] ill, they know well enough that it is an illusion; but if the illness is more severe they actually move according to the appearances. The cause of these occurrences is that the faculty in virtue of which the controlling sense judges is not identical with that in virtue of which images come before the mind. A proof of this is, that the sun presents itself as only a foot in diameter, though often something else gainsays the [20] imagination. Again, when the fingers are crossed, one object seems to be two; but yet we deny that it is two; for sight is more authoritative than touch. Yet, if touch stood alone, we should actually have pronounced the one object to be two. The ground of such false judgments is that any appearances whatever present themselves, not only when its object moves a sense, but also when the sense by itself alone [25] is moved, provided only it be moved in the same manner as it is by the object. For example, to persons sailing past the land seems to move, when it is really the eye that is being moved by something else.
3 · From this it is manifest that the movements based upon sensory impressions, whether the latter are derived from external objects or from causes within the body, not only when persons are awake, but also occur when this [30] affection which is called sleep has come upon them, and at that time they appear more. For by day, while the senses and the intellect are working, they are extruded [461a1] and obscured, just as a smaller is beside a larger fire, or as small beside great pains or pleasures, though, as soon as the latter have ceased, even those which are trifling emerge into notice. But by night owing to the inaction of senses, and their powerlessness to realize themselves, which arises from the reflux of the hot from the [5] exterior parts to the interior, they are borne down to the source of sense-perception, and there display themselves as the disturbance subsides. We must suppose that, like the little eddies which are formed in rivers, so the movements are each a continuous process, often remaining like what they were when first started, but [10] often, too, broken into other forms by collisions with obstacles. This gives the reason why no dreams occur in sleep after meals, or to sleepers who are extremely young, e.g., to infants. The movement in such cases is excessive, owing to the heat generated from the food. Hence, just as in a liquid, if one vehemently disturbs it, sometimes no reflected image appears, while at other times one appears, indeed, but [15] utterly distorted, so as to seem quite unlike its original; while, when once the motion has ceased, the reflected images are clear and plain; in the same manner during sleep the images, or residuary movements, which are based upon the sensory impressions, become sometimes quite obliterated by the above described motion [20] when too violent; while at other times the sights are indeed seen, but confused and weird, and the dreams are incoherent, like those of persons who are atrabilious, or feverish, or intoxicated with wine. For all such affections, being spirituous, cause much commotion and disturbance. In sanguineous animals, in proportion as the blood becomes calm and separated the fact that the movement, based on impressions [25] derived from each of the organs of sense, is preserved in its integrity, renders the dreams coherent, causes an image to present itself, and makes the dreamer think, owing to the effects borne in from the organ of sight, that he actually sees, and owing to those which come from the organ of hearing, that he really hears; and so on with those also which proceed from the other sensory organs. For it is owing to [30] the fact that the movement which reaches the source of sense comes from them, that one even when awake believes himself to see, or hear, or otherwise perceive; just as it [461b1] is from a belief that the organ of sight is being stimulated, though in reality not so stimulated, that we sometimes declare ourselves to see, or that, from the fact that touch announces two movements, we think that the one object is two. For, as a rule, the governing sense affirms the report of each particular sense, unless another particular sense, more authoritative, makes a contradictory report. In every case an appearance presents itself, but what appears does not in every case seem real, unless [5] when the deciding faculty is inhibited, or does not move with its proper motion. Moreover, as we said that different men are subject to illusions, each according to the different emotion present in him, so it is that the sleeper, owing to sleep, and to the movements then going on in his sensory organs, as well as to the other facts of the sensory process, is liable to illusion, so that what has little similarity to [10] something appears to be the thing itself. For when one is asleep, in proportion as most of the blood sinks inwards, so the internal movements, some potential, others actual, accompany it inwards. They are so related that, if anything move the blood, some one sensory movement will emerge from it, while if this perishes another will take its place; while to one another also they are related in the same way as the [15] artificial frogs in water which rise to the surface as the salt becomes dissolved. The residuary movements are like these: they are within the soul potentially, but actualize themselves only when the impediment to their doing so has been relaxed; and according as they are thus set free, they begin to move in the blood which remains in the sensory organs, and which is now but scanty, and take on likenesses after the manner of cloud-shapes, which in their rapid metamorphoses one [20] compares now to human beings and a moment afterwards to centaurs. Each of them is however, as has been said, the remnant of a sensory impression taken when sense was actualizing itself; and when this, the true impression, has departed, its remnant is still there, and it is correct to say of it, that though not actually Coriscus, it is like Coriscus. When the person was actually perceiving, his controlling and judging sensory faculty did not call it Coriscus, but, prompted by this, called the genuine [25] person yonder Coriscus. Accordingly, that which, when actually perceiving, says this (unless completely inhibited by the blood), now, as though it were perceiving, is moved by the movements persisting in the sense-organs, and that which is like the thing seems to it to be the thing itself; and the effect of sleep is so great that it causes this mistake to pass unnoticed. Accordingly, just as if a finger be pressed under the [462a1] eyeball without being observed, one object will not only present two visual images, but will create an opinion of its being two objects; while if it be observed, the presentation will be the same, but the same opinion will not be formed of it; exactly so it is in states of sleep: if the sleeper perceives that he is asleep, and is conscious of the sleeping state during which the perception comes before his mind, it presents itself still, but something within him speaks to this effect: ‘the image of Coriscus [5] presents itself, but the real Coriscus is not present’; for often, when one is asleep, there is something in the soul which declares that what then presents itself is but a dream. If, however, he is not aware of being asleep, there is nothing which will contradict the testimony of the bare presentation.
That what we here urge is true, i.e. that there are such imaginative movements in the sensory organs, any one may convince himself, if he attends to and tries to [10] remember the affections we experience when sinking into slumber or when being awakened. He will sometimes, in the moment of awakening, surprise the images which present themselves to him in sleep, and find that they are really but movements lurking in the organs of sense. And indeed some very young persons, if it is dark, though looking with wide open eyes, see multitudes of phantom figures moving before them, so that they often cover up their heads in terror.
[15] From all this, then, the conclusion to be drawn is, that the dream is a sort of image and, more particularly, one which occurs in sleep; since the phantoms just mentioned are not dreams, nor is any other dream which presents itself when the sense-perceptions are in a state of freedom. Nor is every image which occurs in sleep necessarily a dream. For in the first place, some persons actually, in a certain way, perceive sounds, light, savour, and contact; feebly, however, and, as it were, [20] remotely. For there have been cases in which persons while asleep, but with the eyes partly open, saw faintly in their sleep (as they supposed) the light of a lamp, and afterwards, on being awakened, recognized it at once as the actual light of the lamp; while, in other cases, persons who faintly heard the crowing of cocks or the barking of dogs identified these clearly as soon as they awoke. Some persons, too, return [25] answers to questions put to them in sleep. For it is quite possible that, of waking or sleeping, while the one is present in the ordinary sense, the other also should be present in a certain way. But none of these occurrences should be called a dream. Nor should the true thoughts, as distinct from the images, which occur in sleep. The dream proper is an image based on the movement of sense impressions, when it [30] occurs during sleep, insofar as it is asleep.
There are cases of persons who in their whole lives have never had a dream, while others dream when considerably advanced in years, having never dreamed [462b1] before. The cause of their not having dreams appears somewhat like that which operates in the case of infants, and after meals. It is intelligible enough that no [5] dream-image should occur to persons whose natural constitution is such that in them copious exhalation is borne upwards, which, when borne back downwards, causes a large quantity of motion. But it is not surprising that, as age advances, a dream should at length appear to them. For, when a change has occurred in them in [10] proportion to age or emotional experience, this reversal must occur also.