350 BC
by Aristotle
translated by J. I. Beare

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 affection is one which pertains to the
faculty of intelligence 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 actual 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, motion,
&c., while there are others, as colour, sound, taste, peculiar [each
to its own sense]; 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, so that manifestly 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 [in dreams] we not
only assert, e.g. that some object approaching is a man or a horse
[which would be an exercise of opinion], but that the object is
white or beautiful, points on which opinion without sense-perception
asserts 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. [In
dreams], too, we think something else, over and above the dream
presentation, just as we do in waking 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 mere
phantasms immediately before our minds. This would be manifest to
any one who should attend and try, immediately on arising from
sleep, to remember [his dreaming experience]. There are cases of
persons who have seen such dreams, those, for example, who believe
themselves to be mentally arranging a given list of subjects according
to the mnemonic rule. They frequently find themselves engaged in
something else besides the dream, viz. in setting a phantasm which
they envisage into its mnemonic position. Hence it is plain that not
every 'phantasm' in sleep is a mere dream-image, and that the
further thinking which we perform then is due to an exercise of the
faculty of opinion.
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 to
them to be only a foot wide. Now, whether the presentative faculty
of the soul be identical with, or different from, the faculty of
sense-perception, in either case the illusion does not occur without
our actually seeing or [otherwise] 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 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 duly as when he is awake, gives its impulse in
a certain manner to his [primary] faculty of sense, though not in
precisely the same manner as when he is awake. Sometimes, too, opinion
says [to dreamers] just as to those who are awake, that the object
seen is an illusion; at other times it is inhibited, and becomes a
mere follower of the phantasm.
It is plain therefore that this affection, which we name 'dreaming',
is no mere exercise of opinion or intelligence, but yet is not an
affection of the faculty of perception in the simple sense. If it were
the latter it would be possible [when asleep] 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 [of dreaming] 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.
But since we have, in our work On the Soul, treated of presentation,
and the faculty of presentation is identical with that of
sense-perception, though the essential notion of a faculty of
presentation is different from that of a faculty of
sense-perception; and since presentation is the movement set up by a
sensory faculty when actually discharging its function, while a
dream appears to be a presentation (for a presentation which occurs in
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


We can best obtain a scientific view of the nature of the dream
and the manner in which it originates by regarding it in the light
of the circumstances attending sleep. The 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 when that which set up the movement is no
longer in contact [with the things that are moved]. For that which set
them in motion moves a certain portion of air, and this, in turn,
being moved excites motion in another portion; and so, accordingly, it
is in this way that [the bodies], whether in air or in liquids,
continue moving, until they come to a standstill.
This we must likewise assume to happen in the case of qualitative
change; for that part which [for example] has been heated by something
hot, heats [in turn] the part next to it, and this propagates the
affection continuously onwards until the process has come round to its
oint of origination. This must also happen in the organ wherein the
exercise of sense-perception takes place, since sense-perception, as
realized in actual perceiving, is a mode of 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, 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 excited by the light still
subsisting in our eyes. Also, when we have looked steadily 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
in its own colour; then it changes 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, they find that the visual stimulations
still present themselves, for the things really at rest are then
seen moving: persons become very 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 [in their objects] is shown by what happens
in the case of mirrors; a subject to which, even taking it
independently, one might devote close consideration and inquiry. At
the same time it becomes plain from them that as the eye [in seeing]
is affected [by the object seen], so also it produces a certain effect
upon it. If a woman chances during her menstrual period to look into a
highly polished mirror, the surface of it will grow cloudy with a
blood-coloured haze. It is very hard to remove this stain from a new
mirror, but easier to remove from an older mirror. As we have said
before, the cause of this lies in the fact that in the act of sight
there occurs not only a passion in the sense organ acted on by the
polished surface, but the organ, as an agent, also produces an action,
as is proper to a brilliant object. For sight is the property of an
organ possessing brilliance and colour. The eyes, therefore, have
their proper action as have other parts of the body. Because it is
natural to the eye to be filled with blood-vessels, a woman's eyes,
during the period of menstrual flux and inflammation, will undergo a
change, although her husband will not note this since his seed is of
the same nature as that of his wife. The surrounding atmosphere,
through which operates the action of sight, and which surrounds the
mirror also, will undergo a change of the same sort that occurred
shortly before in the woman's eyes, and hence the surface of the
mirror is likewise affected. And as in the case of a garment, the
cleaner it is the more quickly it is soiled, so the same holds true in
the case of the mirror. For anything that is clean will show quite
clearly a stain that it chances to receive, and the cleanest object
shows up even the slightest stain. A bronze mirror, because of its
shininess, is especially sensitive to any sort of contact (the
movement of the surrounding air acts upon it like a rubbing or
pressing or wiping); on that account, therefore, what is clean will
show up clearly the slightest touch on its surface. It is hard to
cleanse smudges off new mirrors because the stain penetrates deeply
and is suffused to all parts; it penetrates deeply because the
mirror is not a dense medium, and is suffused widely because of the
smoothness of the object. On the other hand, in the case of old
mirrors, stains do not remain because they do not penetrate deeply,
but only smudge the surface.
From this therefore it is plain that stimulatory motion is set up
even by slight differences, and that sense-perception is quick to
respond to it; and further that the organ which perceives colour is
not only affected by its object, but also reacts upon it. 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;
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.
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, 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 illusory impressions.
Thus too, both in fits of anger, and also in all states of appetite,
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, an
illusion arising from 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 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 presentations 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
presentation. Again, when the fingers are crossed, the one object
[placed between them] is felt [by the touch] as 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 judgements is that any appearances
whatever present themselves, not only when its object stimulates a
sense, but also when the sense by itself alone is stimulated, provided
only it be stimulated 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 [the moving ship.]

From this it is manifest that the stimulatory movements based upon
sensory impressions, whether the latter are derived from external
objects or from causes within the body, present themselves not only
when persons are awake, but also then, when this affection which is
called sleep has come upon them, with even greater impressiveness. For
by day, while the senses and the intellect are working together,
they (i.e. such movements) are extruded from consciousness or
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
[i.e. in sleep] owing to the inaction of the particular senses, and
their powerlessness to realize themselves, which arises from the
reflux of the hot from the exterior parts to the interior, they
[i.e. the above 'movements'] are borne in to the head quarters of
sense-perception, and there display themselves as the disturbance
(of waking life) subsides. We must suppose that, like the little
eddies which are being ever formed in rivers, so the sensory movements
are each a continuous process, often remaining like what they were
when first started, but often, too, broken into other forms by
collisions with obstacles. This [last mentioned point], moreover,
gives the reason why no dreams occur in sleep immediately after meals,
or to sleepers who are extremely young, e.g. to infants. The
internal 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 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 phantasms, or residuary movements, which are based upon
the sensory impressions, become sometimes quite obliterated by the
above described motion when too violent; while at other times the
sights are indeed seen, but confused and weird, and the dreams
[which then appear] are unhealthy, 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 as
its purer are separated from its less pure elements, the fact that the
movement, based on impressions derived from each of the organs of
sense, is preserved in its integrity, renders the dreams healthy,
causes a [clear] 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 the fact that the
movement which reaches the primary organ of sense comes from them,
that one even when awake believes himself to see, or hear, or
otherwise perceive; just as it is from a belief that the organ of
sight is being stimulated, though in reality not so stimulated, that
we sometimes erroneously 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 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 the dream presentation, though but little like it, appears as
some actual given thing. For when one is asleep, in proportion as most
of the blood sinks inwards to its fountain [the heart], the internal
[sensory] movements, some potential, others actual accompany it
inwards. They are so related [in general] 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 artificial frogs in water which
severally rise [in fixed succesion] to the surface in the order in
which the salt [which keeps them down] 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, while they possess verisimilitude
after the manner of cloud-shapes, which in their rapid metamorphoses
one 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
immanent, and it is correct to say of it, that though not actually
Koriskos, it is like Koriskos. For when the person was actually
perceiving, his controlling and judging sensory faculty did not call
it Koriskos, but, prompted by this [impression], called the genuine
person yonder Koriskos. Accordingly, this sensory impulse, which, when
actually perceiving, it [the controlling faculty] describes (unless
completely inhibited by the blood), it now [in dreams] when
quasi-perceiving, receives from the movements persisting in the
sense-organs, and mistakes it-an impulse that is merely like the
true [objective] impression-for the true impression itself, while
the effect of sleep is so great that it causes this mistake to pass
unnoticed. Accordingly, just as if a finger be inserted beneath the
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 [the finger] 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 Koriskos presents itself, but the
real Koriskos is not present'; for often, when one is asleep, there is
something in consciousness 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
That what we here urge is true, i.e. that there are such
presentative movements in the sensory organs, any one may convince
himself, if he attends to and tries to 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.
From all this, then, the conclusion to be drawn is, that the dream
is a sort of presentation, and, more particularly, one which occurs in
sleep; since the phantoms just mentioned are not dreams, nor is any
other a dream which presents itself when the sense-perceptions are
in a state of freedom. Nor is every presentation which occurs in sleep
necessarily a dream. For in the first place, some persons [when
asleep] actually, in a certain way, perceive sounds, light, savour,
and contact; feebly, however, and, as it were, 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, straightway recognized
it as the actual light of a real lamp; while, in other cases,
persons who faintly heard the crowing of cocks or the barking of
dogs identified these clearly with the real sounds as soon as they
awoke. Some persons, too, return 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 mere
presentations, which occur in sleep [be called dreams]. The dream
proper is a presentation based on the movement of sense impressions,
when such presentation occurs during sleep, taking sleep in the strict
sense of the term.
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 before. The cause of their not having dreams
appears somewhat like that which operates in the case of infants, and
[that which operates] immediately after meals. It is intelligible
enough that no dream-presentation should occur to persons whose
natural constitution is such that in them copious evaporation 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. Indeed, it is inevitable that, as a change
is wrought in them in proportion to age or emotional experience, this
reversal [from non-dreaming to dreaming] should occur also.


Default Template for Easy Text To HTML Converter