350 BC
by Aristotle
translated by J. I. Beare

HAVING now definitely considered the soul, by itself, and its
several faculties, we must next make a survey of animals and all
living things, in order to ascertain what functions are peculiar,
and what functions are common, to them. What has been already
determined respecting the soul [sc. by itself] must be assumed
throughout. The remaining parts [sc. the attributes of soul and
body conjointly] of our subject must be now dealt with, and we may
begin with those that come first.
The most important attributes of animals, whether common to all or
peculiar to some, are, manifestly, attributes of soul and body in
conjunction, e.g. sensation, memory, passion, appetite and desire in
general, and, in addition pleasure and pain. For these may, in fact,
be said to belong to all animals. But there are, besides these,
certain other attributes, of which some are common to all living
things, while others are peculiar to certain species of animals. The
most important of these may be summed up in four pairs, viz. waking
and sleeping, youth and old age, inhalation and exhalation, life and
death. We must endeavour to arrive at a scientific conception of
these, determining their respective natures, and the causes of their
But it behoves the Physical Philosopher to obtain also a clear
view of the first principles of health and disease, inasmuch as
neither health nor disease can exist in lifeless things. Indeed we may
say of most physical inquirers, and of those physicians who study
their art philosophically, that while the former complete their
works with a disquisition on medicine, the latter usually base their
medical theories on principles derived from Physics.
That all the attributes above enumerated belong to soul and body
in conjunction, is obvious; for they all either imply sensation as a
concomitant, or have it as their medium. Some are either affections or
states of sensation, others, means of defending and safe-guarding
it, while others, again, involve its destruction or negation. Now it
is clear, alike by reasoning and observation, that sensation is
generated in the soul through the medium of the body.
We have already, in our treatise On the Soul, explained the nature
of sensation and the act of perceiving by sense, and the reason why
this affection belongs to animals. Sensation must, indeed, be
attributed to all animals as such, for by its presence or absence we
distinguish essentially between what is and what is not an animal.
But coming now to the special senses severally, we may say that
touch and taste necessarily appertain to all animals, touch, for the
reason given in On the Soul, and taste, because of nutrition. It is by
taste that one distinguishes in food the pleasant from the unpleasant,
so as to flee from the latter and pursue the former: and savour in
general is an affection of nutrient matter.
The senses which operate through external media, viz. smelling,
hearing, seeing, are found in all animals which possess the faculty of
locomotion. To all that possess them they are a means of preservation;
their final cause being that such creatures may, guided by
antecedent perception, both pursue their food, and shun things that
are bad or destructive. But in animals which have also intelligence
they serve for the attainment of a higher perfection. They bring in
tidings of many distinctive qualities of things, from which the
knowledge of truth, speculative and practical, is generated in the
Of the two last mentioned, seeing, regarded as a supply for the
primary wants of life, and in its direct effects, is the superior
sense; but for developing intelligence, and in its indirect
consequences, hearing takes the precedence. The faculty of seeing,
thanks to the fact that all bodies are coloured, brings tidings of
multitudes of distinctive qualities of all sorts; whence it is through
this sense especially that we perceive the common sensibles, viz.
figure, magnitude, motion, number: while hearing announces only the
distinctive qualities of sound, and, to some few animals, those also
of voice. indirectly, however, it is hearing that contributes most
to the growth of intelligence. For rational discourse is a cause of
instruction in virtue of its being audible, which it is, not directly,
but indirectly; since it is composed of words, and each word is a
thought-symbol. Accordingly, of persons destitute from birth of either
sense, the blind are more intelligent than the deaf and dumb.

Of the distinctive potency of each of the faculties of sense
enough has been said already.
But as to the nature of the sensory organs, or parts of the body
in which each of the senses is naturally implanted, inquirers now
usually take as their guide the fundamental elements of bodies. Not,
however, finding it easy to coordinate five senses with four elements,
they are at a loss respecting the fifth sense. But they hold the organ
of sight to consist of fire, being prompted to this view by a
certain sensory affection of whose true cause they are ignorant.
This is that, when the eye is pressed or moved, fire appears to
flash from it. This naturally takes place in darkness, or when the
eyelids are closed, for then, too, darkness is produced.
This theory, however, solves one question only to raise another;
for, unless on the hypothesis that a person who is in his full
senses can see an object of vision without being aware of it, the
eye must on this theory see itself. But then why does the above
affection not occur also when the eye is at rest? The true explanation
of this affection, which will contain the answer to our question,
and account for the current notion that the eye consists of fire, must
be determined in the following way: Things which are smooth have the
natural property of shining in darkness, without, however, producing
light. Now, the part of the eye called 'the black', i.e. its central
part, is manifestly smooth. The phenomenon of the flash occurs only
when the eye is moved, because only then could it possibly occur
that the same one object should become as it were two. The rapidity of
the movement has the effect of making that which sees and that which
is seen seem different from one another. Hence the phenomenon does not
occur unless the motion is rapid and takes place in darkness. For it
is in the dark that that which is smooth, e.g. the heads of certain
fishes, and the sepia of the cuttle-fish, naturally shines, and,
when the movement of the eye is slow, it is impossible that that which
sees and that which is seen should appear to be simultaneously two and
one. But, in fact, the eye sees itself in the above phenomenon
merely as it does so in ordinary optical reflexion.
If the visual organ proper really were fire, which is the doctrine
of Empedocles, a doctrine taught also in the Timaeus, and if vision
were the result of light issuing from the eye as from a lantern, why
should the eye not have had the power of seeing even in the dark? It
is totally idle to say, as the Timaeus does, that the visual ray
coming forth in the darkness is quenched. What is the meaning of
this 'quenching' of light? That which, like a fire of coals or an
ordinary flame, is hot and dry is, indeed, quenched by the moist or
cold; but heat and dryness are evidently not attributes of light. Or
if they are attributes of it, but belong to it in a degree so slight
as to be imperceptible to us, we should have expected that in the
daytime the light of the sun should be quenched when rain falls, and
that darkness should prevail in frosty weather. Flame, for example,
and ignited bodies are subject to such extinction, but experience
shows that nothing of this sort happens to the sunlight.
Empedocles at times seems to hold that vision is to be explained
as above stated by light issuing forth from the eye, e.g. in the
following passage:-

As when one who purposes going abroad prepares a lantern,
A gleam of fire blazing through the stormy night,
Adjusting thereto, to screen it from all sorts of winds,
transparent sides,
Which scatter the breath of the winds as they blow,
While, out through them leaping, the fire,
i.e. all the more subtile part of this,
Shines along his threshold old incessant beams:
So [Divine love] embedded the round "lens", [viz.]
the primaeval fire fenced within the membranes,
In [its own] delicate tissues;
And these fended off the deep surrounding flood,
While leaping forth the fire, i.e. all its more subtile part-.

Sometimes he accounts for vision thus, but at other times he
explains it by emanations from the visible objects.
Democritus, on the other hand, is right in his opinion that the
eye is of water; not, however, when he goes on to explain seeing as
mere mirroring. The mirroring that takes place in an eye is due to the
fact that the eye is smooth, and it really has its seat not in the eye
which is seen, but in that which sees. For the case is merely one of
reflexion. But it would seem that even in his time there was no
scientific knowledge of the general subject of the formation of images
and the phenomena of reflexion. It is strange too, that it never
occurred to him to ask why, if his theory be true, the eye alone sees,
while none of the other things in which images are reflected do so.
True, then, the visual organ proper is composed of water, yet vision
appertains to it not because it is so composed, but because it is
translucent- a property common alike to water and to air. But water
is more easily confined and more easily condensed than air;
wherefore it is that the pupil, i.e. the eye proper, consists of
water. That it does so is proved by facts of actual experience. The
substance which flows from eyes when decomposing is seen to be
water, and this in undeveloped embryos is remarkably cold and
glistening. In sanguineous animals the white of the eye is fat and
oily, in order that the moisture of the eye may be proof against
freezing. Wherefore the eye is of all parts of the body the least
sensitive to cold: no one ever feels cold in the part sheltered by the
eyelids. The eyes of bloodless animals are covered with a hard scale
which gives them similar protection.
It is, to state the matter generally, an irrational notion that
the eye should see in virtue of something issuing from it; that the
visual ray should extend itself all the way to the stars, or else go
out merely to a certain point, and there coalesce, as some say, with
rays which proceed from the object. It would be better to suppose this
coalescence to take place in the fundament of the eye itself. But even
this would be mere trifling. For what is meant by the 'coalescence' of
light with light? Or how is it possible? Coalescence does not occur
between any two things taken at random. And how could the light within
the eye coalesce with that outside it? For the environing membrane
comes between them.
That without light vision is impossible has been stated elsewhere;
but, whether the medium between the eye and its objects is air or
light, vision is caused by a process through this medium.
Accordingly, that the inner part of the eye consists of water is
easily intelligible, water being translucent.
Now, as vision outwardly is impossible without [extra-organic]
light, so also it is impossible inwardly [without light within the
organ]. There must, therefore, be some translucent medium within the
eye, and, as this is not air, it must be water. The soul or its
perceptive part is not situated at the external surface of the eye,
but obviously somewhere within: whence the necessity of the interior
of the eye being translucent, i.e. capable of admitting light. And
that it is so is plain from actual occurrences. It is matter of
experience that soldiers wounded in battle by a sword slash on the
temple, so inflicted as to sever the passages of [i.e. inward from]
the eye, feel a sudden onset of darkness, as if a lamp had gone out;
because what is called the pupil, i.e. the translucent, which is a
sort of inner lamp, is then cut off [from its connexion with the
Hence, if the facts be at all as here stated, it is clear that- if
one should explain the nature of the sensory organs in this way,
i.e. by correlating each of them with one of the four elements,- we
must conceive that the part of the eye immediately concerned in vision
consists of water, that the part immediately concerned in the
perception of sound consists of air, and that the sense of smell
consists of fire. (I say the sense of smell, not the organ.) For the
organ of smell is only potentially that which the sense of smell, as
realized, is actually; since the object of sense is what causes the
actualization of each sense, so that it (the sense) must (at the
instant of actualization) be (actually) that which before (the
moment of actualization) it was potentially. Now, odour is a
smoke-like evaporation, and smoke-like evaporation arises from fire.
This also helps us to understand why the olfactory organ has its
proper seat in the environment of the brain, for cold matter is
potentially hot. In the same way must the genesis of the eye be
explained. Its structure is an offshoot from the brain, because the
latter is the moistest and coldest of all the bodily parts.
The organ of touch proper consists of earth, and the faculty of
taste is a particular form of touch. This explains why the sensory
organ of both touch and taste is closely related to the heart. For the
heart as being the hottest of all the bodily parts, is the
counterpoise of the brain.
This then is the way in which the characteristics of the bodily
organs of sense must be determined.

Of the sensibles corresponding to each sensory organ, viz. colour,
sound, odour, savour, touch, we have treated in On the Soul in general
terms, having there determined what their function is, and what is
implied in their becoming actualized in relation to their respective
organs. We must next consider what account we are to give of any one
of them; what, for example, we should say colour is, or sound, or
odour, or savour; and so also respecting [the object of] touch. We
begin with colour.
Now, each of them may be spoken of from two points of view, i.e.
either as actual or as potential. We have in On the Soul explained
in what sense the colour, or sound, regarded as actualized [for
sensation] is the same as, and in what sense it is different from, the
correlative sensation, the actual seeing or hearing. The point of
our present discussion is, therefore, to determine what each
sensible object must be in itself, in order to be perceived as it is
in actual consciousness.
We have already in On the Soul stated of Light that it is the colour
of the Translucent, [being so related to it] incidentally; for
whenever a fiery element is in a translucent medium presence there
is Light; while the privation of it is Darkness. But the
'Translucent', as we call it, is not something peculiar to air, or
water, or any other of the bodies usually called translucent, but is a
common 'nature' and power, capable of no separate existence of its
own, but residing in these, and subsisting likewise in all other
bodies in a greater or less degree. As the bodies in which it subsists
must have some extreme bounding surface, so too must this. Here, then,
we may say that Light is a 'nature' inhering in the Translucent when
the latter is without determinate boundary. But it is manifest that,
when the Translucent is in determinate bodies, its bounding extreme
must be something real; and that colour is just this 'something' we
are plainly taught by facts-colour being actually either at the
external limit, or being itself that limit, in bodies. Hence it was
that the Pythagoreans named the superficies of a body its 'hue', for
'hue', indeed, lies at the limit of the body; but the limit of the
body; is not a real thing; rather we must suppose that the same
natural substance which, externally, is the vehicle of colour exists
[as such a possible vehicle] also in the interior of the body.
Air and water, too [i.e. as well as determinately bounded bodies]
are seen to possess colour; for their brightness is of the nature of
colour. But the colour which air or sea presents, since the body in
which it resides is not determinately bounded, is not the same when
one approaches and views it close by as it is when one regards it from
a distance; whereas in determinate bodies the colour presented is
definitely fixed, unless, indeed, when the atmospheric environment
causes it to change. Hence it is clear that that in them which is
susceptible of colour is in both cases the same. It is therefore the
Translucent, according to the degree to which it subsists in bodies
(and it does so in all more or less), that causes them to partake of
colour. But since the colour is at the extremity of the body, it
must be at the extremity of the Translucent in the body. Whence it
follows that we may define colour as the limit of the Translucent in
determinately bounded body. For whether we consider the special
class of bodies called translucent, as water and such others, or
determinate bodies, which appear to possess a fixed colour of their
own, it is at the exterior bounding surface that all alike exhibit
their colour.
Now, that which when present in air produces light may be present
also in the Translucent which pervades determinate bodies; or again,
it may not be present, but there may be a privation of it.
Accordingly, as in the case of air the one condition is light, the
other darkness, in the same way the colours White and Black are
generated in determinate bodies.
We must now treat of the other colours, reviewing the several
hypotheses invented to explain their genesis.
(1) It is conceivable that the White and the Black should be
juxtaposed in quantities so minute that [a particle of] either
separately would be invisible, though the joint product [of two
particles, a black and a white] would be visible; and that they should
thus have the other colours for resultants. Their product could, at
all events, appear neither white nor black; and, as it must have
some colour, and can have neither of these, this colour must be of a
character- in fact, a species of colour different from either. Such,
then, is a possible way of conceiving the existence of a plurality
of colours besides the White and Black; and we may suppose that [of
this 'plurality'] many are the result of a [numerical] ratio; for
the blacks and whites may be juxtaposed in the ratio of 3 to 2 or of 3
to 4, or in ratios expressible by other numbers; while some may be
juxtaposed according to no numerically expressible ratio, but
according to some relation of excess or defect in which the blacks and
whites involved would be incommensurable quantities; and, accordingly,
we may regard all these colours [viz. all those based on numerical
ratios] as analogous to the sounds that enter into music, and
suppose that those involving simple numerical ratios, like the
concords in music, may be those generally regarded as most
agreeable; as, for example, purple, crimson, and some few such
colours, their fewness being due to the same causes which render the
concords few. The other compound colours may be those which are not
based on numbers. Or it may be that, while all colours whatever
[except black and white] are based on numbers, some are regular in
this respect, others irregular; and that the latter [though now
supposed to be all based on numbers], whenever they are not pure,
owe this character to a corresponding impurity in [the arrangement of]
their numerical ratios. This then is one conceivable hypothesis to
explain the genesis of intermediate colours.
(2) Another is that the Black and White appear the one through the
medium of the other, giving an effect like that sometimes produced
by painters overlaying a less vivid upon a more vivid colour, as
when they desire to represent an object appearing under water or
enveloped in a haze, and like that produced by the sun, which in
itself appears white, but takes a crimson hue when beheld through a
fog or a cloud of smoke. On this hypothesis, too, a variety of colours
may be conceived to arise in the same way as that already described;
for between those at the surface and those underneath a definite ratio
might sometimes exist; in other cases they might stand in no
determinate ratio. To [introduce a theory of colour which would set
all these hypotheses aside, and] say with the ancients that colours
are emanations, and that the visibility of objects is due to such a
cause, is absurd. For they must, in any case, explain sense-perception
through Touch; so that it were better to say at once that visual
perception is due to a process set up by the perceived object in the
medium between this object and the sensory organ; due, that is, to
contact [with the medium affected,] not to emanations.
If we accept the hypothesis of juxtaposition, we must assume not
only invisible magnitude, but also imperceptible time, in order that
the succession in the arrival of the stimulatory movements may be
unperceived, and that the compound colour seen may appear to be one,
owing to its successive parts seeming to present themselves at once.
On the hypothesis of superposition, however, no such assumption is
needful: the stimulatory process produced in the medium by the upper
colour, when this is itself unaffected, will be different in kind from
that produced by it when affected by the underlying colour. Hence it
presents itself as a different colour, i.e. as one which is neither
white nor black. So that, if it is impossible to suppose any magnitude
to be invisible, and we must assume that there is some distance from
which every magnitude is visible, this superposition theory, too [i.e.
as well as No. 3 infra], might pass as a real theory of
colour-mixture. Indeed, in the previous case also there is no reason
why, to persons at a distance from the juxtaposed blacks and whites,
some one colour should not appear to present itself as a blend of
both. [But it would not be so on a nearer view], for it will be shown,
in a discussion to be undertaken later on, that there is no
magnitude absolutely invisible.
(3) There is a mixture of bodies, however, not merely such as some
suppose, i.e. by juxtaposition of their minimal parts, which, owing to
[the weakness of our] sense, are imperceptible by us, but a mixture by
which they [i.e. the 'matter' of which they consist] are wholly
blent together by interpenetration, as we have described it in the
treatise on Mixture, where we dealt with this subject generally in its
most comprehensive aspect. For, on the supposition we are criticizing,
the only totals capable of being mixed are those which are divisible
into minimal parts, [e.g. genera into individuals] as men, horses,
or the [various kinds of] seeds. For of mankind as a whole the
individual man is such a least part; of horses [as an aggregate] the
individual horse. Hence by the juxtaposition of these we obtain a
mixed total, consisting [like a troop of cavalry] of both together;
but we do not say that by such a process any individual man has been
mixed with any individual horse. Not in this way, but by complete
interpenetration [of their matter], must we conceive those things to
be mixed which are not divisible into minima; and it is in the case of
these that natural mixture exhibits itself in its most perfect form.
We have explained already in our discourse 'On Mixture' how such
mixture is possible. This being the true nature of mixture, it is
plain that when bodies are mixed their colours also are necessarily
mixed at the same time; and [it is no less plain] that this is the
real cause determining the existence of a plurality of colours- not
superposition or juxtaposition. For when bodies are thus mixed,
their resultant colour presents itself as one and the same at all
distances alike; not varying as it is seen nearer or farther away.
Colours will thus, too [as well as on the former hypotheses], be
many in number on account of the fact that the ingredients may be
combined with one another in a multitude of ratios; some will be based
on determinate numerical ratios, while others again will have as their
basis a relation of quantitative excess or defect not expressible in
integers. And all else that was said in reference to the colours,
considered as juxtaposed or superposed, may be said of them likewise
when regarded as mixed in the way just described.
Why colours, as well as savours and sounds, consist of species
determinate [in themselves] and not infinite [in number] is a question
which we shall discuss hereafter.

We have now explained what colour is, and the reason why there are
many colours; while before, in our work On the Soul, we explained
the nature of sound and voice. We have next to speak of Odour and
Savour, both of which are almost the same physical affection, although
they each have their being in different things. Savours, as a class,
display their nature more clearly to us than Odours, the cause of
which is that the olfactory sense of man is inferior in acuteness to
that of the lower animals, and is, when compared with our other
senses, the least perfect of Man's sense of Touch, on the contrary,
excels that of all other animals in fineness, and Taste is a
modification of Touch.
Now the natural substance water per se tends to be tasteless. But
[since without water tasting is impossible] either (a) we must suppose
that water contains in itself [uniformly diffused through it] the
various kinds of savour, already formed, though in amounts so small as
to be imperceptible, which is the doctrine of Empedocles; or (b) the
water must be a sort of matter, qualified, as it were, to produce
germs of savours of all kinds, so that all kinds of savour are
generated from the water, though different kinds from its different
parts, or else (c) the water is in itself quite undifferentiated in
respect of savour [whether developed or undeveloped], but some
agent, such for example as one might conceive Heat or the Sun to be,
is the efficient cause of savour.
(a) Of these three hypotheses, the falsity of that held by
Empedocles is only too evident. For we see that when pericarpal fruits
are plucked [from the tree] and exposed in the sun, or subjected to
the action of fire, their sapid juices are changed by the heat,
which shows that their qualities are not due to their drawing anything
from the water in the ground, but to a change which they undergo
within the pericarp itself; and we see, moreover, that these juices,
when extracted and allowed to lie, instead of sweet become by lapse of
time harsh or bitter, or acquire savours of any and every sort; and
that, again, by the process of boiling or fermentation they are made
to assume almost all kinds of new savours.
(b) It is likewise impossible that water should be a material
qualified to generate all kinds of Savour germs [so that different
savours should arise out of different parts of the water]; for we
see different kinds of taste generated from the same water, having
it as their nutriment.
(C) It remains, therefore, to suppose that the water is changed by
passively receiving some affection from an external agent. Now, it
is manifest that water does not contract the quality of sapidity
from the agency of Heat alone. For water is of all liquids the
thinnest, thinner even than oil itself, though oil, owing to its
viscosity, is more ductile than water, the latter being uncohesive
in its particles; whence water is more difficult than oil to hold in
the hand without spilling. But since perfectly pure water does not,
when subjected to the action of Heat, show any tendency to acquire
consistency, we must infer that some other agency than heat is the
cause of sapidity. For all savours [i.e. sapid liquors] exhibit a
comparative consistency. Heat is, however, a coagent in the matter.
Now the sapid juices found in pericarpal fruits evidently exist also
in the earth. Hence many of the old natural philosophers assert that
water has qualities like those of the earth through which it flows,
a fact especially manifest in the case of saline springs, for salt
is a form of earth. Hence also when liquids are filtered through
ashes, a bitter substance, the taste they yield is bitter. There are
many wells, too, of which some are bitter, others acid, while others
exhibit other tastes of all kinds.
As was to be anticipated, therefore, it is in the vegetable
kingdom that tastes occur in richest variety. For, like all things
else, the Moist, by nature's law, is affected only by its contrary;
and this contrary is the Dry. Thus we see why the Moist is affected by
Fire, which as a natural substance, is dry. Heat is, however, the
essential property of Fire, as Dryness is of Earth, according to
what has been said in our treatise on the elements. Fire and Earth,
therefore, taken absolutely as such, have no natural power to
affect, or be affected by, one another; nor have any other pair of
substances. Any two things can affect, or be affected by, one
another only so far as contrariety to the other resides in either of
As, therefore, persons washing Colours or Savours in a liquid
cause the water in which they wash to acquire such a quality [as
that of the colour or savour], so nature, too, by washing the Dry
and Earthy in the Moist, and by filtering the latter, that is,
moving it on by the agency of heat through the dry and earthy, imparts
to it a certain quality. This affection, wrought by the aforesaid
Dry in the Moist, capable of transforming the sense of Taste from
potentiality to actuality, is Savour. Savour brings into actual
exercise the perceptive faculty which pre-existed only in potency. The
activity of sense-perception in general is analogous, not to the
process of acquiring knowledge, but to that of exercising knowledge
already acquired.
That Savours, either as a quality or as the privation of a
quality, belong not to every form of the Dry but to the Nutrient, we
shall see by considering that neither the Dry without the Moist, nor
the Moist without the Dry, is nutrient. For no single element, but
only composite substance, constitutes nutriment for animals. Now,
among the perceptible elements of the food which animals assimilate,
the tangible are the efficient causes of growth and decay; it is qua
hot or cold that the food assimilated causes these; for the heat or
cold is the direct cause of growth or decay. It is qua gustable,
however, that the assimilated food supplies nutrition. For all
organisms are nourished by the Sweet [i.e. the 'gustable' proper],
either by itself or in combination with other savours. Of this we must
speak with more precise detail in our work on Generation: for the
present we need touch upon it only so far as our subject here
requires. Heat causes growth, and fits the food-stuff for
alimentation; it attracts [into the organic system] that which is
light [viz. the sweet], while the salt and bitter it rejects because
of their heaviness. In fact, whatever effects external heat produces
in external bodies, the same are produced by their internal heat in
animal and vegetable organisms. Hence it is [i.e. by the agency of
heat as described] that nourishment is effected by the sweet. The
other savours are introduced into and blended in food [naturally] on a
principle analogous to that on which the saline or the acid is used
artificially, i.e. for seasoning. These latter are used because they
counteract the tendency of the sweet to be too nutrient, and to
float on the stomach.
As the intermediate colours arise from the mixture of white and
black, so the intermediate savours arise from the Sweet and Bitter;
and these savours, too, severally involve either a definite ratio,
or else an indefinite relation of degree, between their components,
either having certain integral numbers at the basis of their
mixture, and, consequently, of their stimulative effect, or else being
mixed in proportions not arithmetically expressible. The tastes
which give pleasure in their combination are those which have their
components joined in a definite ratio.
The sweet taste alone is Rich, [therefore the latter may be regarded
as a variety of the former], while [so far as both imply privation
of the Sweet] the Saline is fairly identical with the Bitter.
Between the extremes of sweet and bitter come the Harsh, the
Pungent, the Astringent, and the Acid. Savours and Colours, it will be
observed, contain respectively about the same number of species. For
there are seven species of each, if, as is reasonable, we regard Dun
[or Grey] as a variety of Black (for the alternative is that Yellow
should be classed with White, as Rich with Sweet); while [the
irreducible colours, viz.] Crimson, Violet, leek-Green, and deep Blue,
come between White and Black, and from these all others are derived by
Again, as Black is a privation of White in the Translucent, so
Saline or Bitter is a privation of Sweet in the Nutrient Moist. This
explains why the ash of all burnt things is bitter; for the potable
[sc. the sweet] moisture has been exuded from them.
Democritus and most of the natural philosophers who treat of
sense-perception proceed quite irrationally, for they represent all
objects of sense as objects of Touch. Yet, if this is really so, it
clearly follows that each of the other senses is a mode of Touch;
but one can see at a glance that this is impossible.
Again, they treat the percepts common to all senses as proper to
one. For [the qualities by which they explain taste viz.] Magnitude
and Figure, Roughness and Smoothness, and, moreover, the Sharpness and
Bluntness found in solid bodies, are percepts common to all the
senses, or if not to all, at least to Sight and Touch. This explains
why it is that the senses are liable to err regarding them, while no
such error arises respecting their proper sensibles; e.g. the sense of
Seeing is not deceived as to Colour, nor is that of Hearing as to
On the other hand, they reduce the proper to common sensibles, as
Democritus does with White and Black; for he asserts that the latter
is [a mode of the] rough, and the former [a mode of the] smooth, while
he reduces Savours to the atomic figures. Yet surely no one sense, or,
if any, the sense of Sight rather than any other, can discern the
common sensibles. But if we suppose that the sense of Taste is
better able to do so, then- since to discern the smallest objects in
each kind is what marks the acutest sense-Taste should have been the
sense which best perceived the common sensibles generally, and
showed the most perfect power of discerning figures in general.
Again, all the sensibles involve contrariety; e.g. in Colour White
is contrary to Black, and in Savours Bitter is contrary to Sweet;
but no one figure is reckoned as contrary to any other figure. Else,
to which of the possible polygonal figures [to which Democritus
reduces Bitter] is the spherical figure [to which he reduces Sweet]
Again, since figures are infinite in number, savours also should
be infinite; [the possible rejoinder- 'that they are so, only that
some are not perceived'- cannot be sustained] for why should one
savour be perceived, and another not?
This completes our discussion of the object of Taste, i.e. Savour;
for the other affections of Savours are examined in their proper place
in connection with the natural history of Plants.

Our conception of the nature of Odours must be analogous to that
of Savours; inasmuch as the Sapid Dry effects in air and water
alike, but in a different province of sense, precisely what the Dry
effects in the Moist of water only. We customarily predicate
Translucency of both air and water in common; but it is not qua
translucent that either is a vehicle of odour, but qua possessed of
a power of washing or rinsing [and so imbibing] the Sapid Dryness.
For the object of Smell exists not in air only: it also exists in
water. This is proved by the case of fishes and testacea, which are
seen to possess the faculty of smell, although water contains no air
(for whenever air is generated within water it rises to the
surface), and these creatures do not respire. Hence, if one were to
assume that air and water are both moist, it would follow that Odour
is the natural substance consisting of the Sapid Dry diffused in the
Moist, and whatever is of this kind would be an object of Smell.
That the property of odorousness is based upon the Sapid may be seen
by comparing the things which possess with those which do not
possess odour. The elements, viz. Fire, Air, Earth, Water, are
inodorous, because both the dry and the moist among them are without
sapidity, unless some added ingredient produces it. This explains
why sea-water possesses odour, for [unlike 'elemental' water] it
contains savour and dryness. Salt, too, is more odorous than natron,
as the oil which exudes from the former proves, for natron is allied
to ['elemental'] earth more nearly than salt. Again, a stone is
inodorous, just because it is tasteless, while, on the contrary,
wood is odorous, because it is sapid. The kinds of wood, too, which
contain more ['elemental'] water are less odorous than others.
Moreover, to take the case of metals, gold is inodorous because it
is without taste, but bronze and iron are odorous; and when the
[sapid] moisture has been burnt out of them, their slag is, in all
cases, less odorous the metals [than the metals themselves]. Silver
and tin are more odorous than the one class of metals, less so than
the other, inasmuch as they are water [to a greater degree than the
former, to a less degree than the latter].
Some writers look upon Fumid exhalation, which is a compound of
Earth and Air, as the essence of Odour. [Indeed all are inclined to
rush to this theory of Odour.] Heraclitus implied his adherence to
it when he declared that if all existing things were turned into
Smoke, the nose would be the organ to discern them with. All writers
incline to refer odour to this cause [sc. exhalation of some sort],
but some regard it as aqueous, others as fumid, exhalation; while
others, again, hold it to be either. Aqueous exhalation is merely a
form of moisture, but fumid exhalation is, as already remarked,
composed of Air and Earth. The former when condensed turns into water;
the latter, in a particular species of earth. Now, it is unlikely that
odour is either of these. For vaporous exhalation consists of mere
water [which, being tasteless, is inodorous]; and fumid exhalation
cannot occur in water at all, though, as has been before stated,
aquatic creatures also have the sense of smell.
Again, the exhalation theory of odour is analogous to the theory
of emanations. If, therefore, the latter is untenable, so, too, is the
It is clearly conceivable that the Moist, whether in air (for air,
too, is essentially moist) or in water, should imbibe the influence
of, and have effects wrought in it by, the Sapid Dryness. Moreover, if
the Dry produces in moist media, i.e. water and air, an effect as of
something washed out in them, it is manifest that odours must be
something analogous to savours. Nay, indeed, this analogy is, in
some instances, a fact [registered in language]; for odours as well as
savours are spoken of as pungent, sweet, harsh, astringent rich
[='savoury']; and one might regard fetid smells as analogous to bitter
tastes; which explains why the former are offensive to inhalation as
the latter are to deglutition. It is clear, therefore, that Odour is
in both water and air what Savour is in water alone. This explains why
coldness and freezing render Savours dull, and abolish odours
altogether; for cooling and freezing tend to annul the kinetic heat
which helps to fabricate sapidity.
There are two species of the Odorous. For the statement of certain
writers that the odorous is not divisible into species is false; it is
so divisible. We must here define the sense in which these species are
to be admitted or denied.
One class of odours, then, is that which runs parallel, as has
been observed, to savours: to odours of this class their
pleasantness or unpleasantness belongs incidentally. For owing to
the fact that Savours are qualities of nutrient matter, the odours
connected with these [e.g. those of a certain food] are agreeable as
long as animals have an appetite for the food, but they are not
agreeable to them when sated and no longer in want of it; nor are they
agreeable, either, to those animals that do not like the food itself
which yields the odours. Hence, as we observed, these odours are
pleasant or unpleasant incidentally, and the same reasoning explains
why it is that they are perceptible to all animals in common.
The other class of odours consists of those agreeable in their
essential nature, e.g. those of flowers. For these do not in any
degree stimulate animals to food, nor do they contribute in any way to
appetite; their effect upon it, if any, is rather the opposite. For
the verse of Strattis ridiculing Euripides-

Use not perfumery to flavour soup,

contains a truth.
Those who nowadays introduce such flavours into beverages deforce
our sense of pleasure by habituating us to them, until, from two
distinct kinds of sensations combined, pleasure arises as it might
from one simple kind.
Of this species of odour man alone is sensible; the other, viz. that
correlated with Tastes, is, as has been said before, perceptible
also to the lower animals. And odours of the latter sort, since
their pleasureableness depends upon taste, are divided into as many
species as there are different tastes; but we cannot go on to say this
of the former kind of odour, since its nature is agreeable or
disagreeable per se. The reason why the perception of such odours is
peculiar to man is found in the characteristic state of man's brain.
For his brain is naturally cold, and the blood which it contains in
its vessels is thin and pure but easily cooled (whence it happens that
the exhalation arising from food, being cooled by the coldness of this
region, produces unhealthy rheums); therefore it is that odours of
such a species have been generated for human beings, as a safeguard to
health. This is their sole function, and that they perform it is
evident. For food, whether dry or moist, though sweet to taste, is
often unwholesome; whereas the odour arising from what is fragrant,
that odour which is pleasant in its own right, is, so to say, always
beneficial to persons in any state of bodily health whatever.
For this reason, too, the perception of odour [in general]
effected through respiration, not in all animals, but in man and
certain other sanguineous animals, e.g. quadrupeds, and all that
participate freely in the natural substance air; because when
odours, on account of the lightness of the heat in them, mount to
the brain, the health of this region is thereby promoted. For odour,
as a power, is naturally heat-giving. Thus Nature has employed
respiration for two purposes: primarily for the relief thereby brought
to the thorax, secondarily for the inhalation of odour. For while an
animal is inhaling,- odour moves in through its nostrils, as it were
'from a side-entrance.'
But the perception of the second class of odours above described
[does not belong to all animal, but] is confined to human beings,
because man's brain is, in proportion to his whole bulk, larger and
moister than the brain of any other animal. This is the reason of
the further fact that man alone, so to speak, among animals
perceives and takes pleasure in the odours of flowers and such things.
For the heat and stimulation set up by these odours are commensurate
with the excess of moisture and coldness in his cerebral region. On
all the other animals which have lungs, Nature has bestowed their
due perception of one of the two kinds of odour [i.e. that connected
with nutrition] through the act of respiration, guarding against the
needless creation of two organs of sense; for in the fact that they
respire the other animals have already sufficient provision for
their perception of the one species of odour only, as human beings
have for their perception of both.
But that creatures which do not respire have the olfactory sense
is evident. For fishes, and all insects as a class, have, thanks to
the species of odour correlated with nutrition, a keen olfactory sense
of their proper food from a distance, even when they are very far away
from it; such is the case with bees, and also with the class of
small ants, which some denominate knipes. Among marine animals, too,
the murex and many other similar animals have an acute perception of
their food by its odour.
It is not equally certain what the organ is whereby they so
perceive. This question, of the organ whereby they perceive odour, may
well cause a difficulty, if we assume that smelling takes place in
animals only while respiring (for that this is the fact is manifest in
all the animals which do respire), whereas none of those just
mentioned respires, and yet they have the sense of smell- unless,
indeed, they have some other sense not included in the ordinary
five. This supposition is, however, impossible. For any sense which
perceives odour is a sense of smell, and this they do perceive, though
probably not in the same way as creatures which respire, but when
the latter are respiring the current of breath removes something
that is laid like a lid upon the organ proper (which explains why they
do not perceive odours when not respiring); while in creatures which
do not respire this is always off: just as some animals have eyelids
on their eyes, and when these are not raised they cannot see,
whereas hard-eyed animals have no lids, and consequently do not
need, besides eyes, an agency to raise the lids, but see straightway
[without intermission] from the actual moment at which it is first
possible for them to do so [i.e. from the moment when an object
first comes within their field of vision].
Consistently with what has been said above, not one of the lower
animals shows repugnance to the odour of things which are
essentially ill-smelling, unless one of the latter is positively
pernicious. They are destroyed, however, by these things, just as
human beings are; i.e. as human beings get headaches from, and are
often asphyxiated by, the fumes of charcoal, so the lower animals
perish from the strong fumes of brimstone and bituminous substances;
and it is owing to experience of such effects that they shun these.
For the disagreeable odour in itself they care nothing whatever
(though the odours of many plants are essentially disagreeable),
unless, indeed, it has some effect upon the taste of their food.
The senses making up an odd number, and an odd number having
always a middle unit, the sense of smell occupies in itself as it were
a middle position between the tactual senses, i.e. Touch and Taste,
and those which perceive through a medium, i.e. Sight and Hearing.
Hence the object of smell, too, is an affection of nutrient substances
(which fall within the class of Tangibles), and is also an affection
of the audible and the visible; whence it is that creatures have the
sense of smell both in air and water. Accordingly, the object of smell
is something common to both of these provinces, i.e. it appertains
both to the tangible on the one hand, and on the other to the
audible and translucent. Hence the propriety of the figure by which it
has been described by us as an immersion or washing of dryness in
the Moist and Fluid. Such then must be our account of the sense in
which one is or is not entitled to speak of the odorous as having
The theory held by certain of the Pythagoreans, that some animals
are nourished by odours alone, is unsound. For, in the first place, we
see that food must be composite, since the bodies nourished by it
are not simple. This explains why waste matter is secreted from
food, either within the organisms, or, as in plants, outside them. But
since even water by itself alone, that is, when unmixed, will not
suffice for food- for anything which is to form a consistency must be
corporeal-, it is still much less conceivable that air should be so
corporealized [and thus fitted to be food]. But, besides this, we
see that all animals have a receptacle for food, from which, when it
has entered, the body absorbs it. Now, the organ which perceives odour
is in the head, and odour enters with the inhalation of the breath; so
that it goes to the respiratory region. It is plain, therefore, that
odour, qua odour, does not contribute to nutrition; that, however,
it is serviceable to health is equally plain, as well by immediate
perception as from the arguments above employed; so that odour is in
relation to general health what savour is in the province of nutrition
and in relation to the bodies nourished.
This then must conclude our discussion of the several organs of

One might ask: if every body is infinitely divisible, are its
sensible qualities- Colour, Savour, Odour, Sound, Weight, Cold or
Heat, [Heaviness or] Lightness, Hardness or Softness-also infinitely
divisible? Or, is this impossible?
[One might well ask this question], because each of them is
productive of sense-perception, since, in fact, all derive their
name [of 'sensible qualities'] from the very circumstance of their
being able to stimulate this. Hence, [if this is so] both our
perception of them should likewise be divisible to infinity, and every
part of a body [however small] should be a perceptible magnitude.
For it is impossible, e.g. to see a thing which is white but not of
a certain magnitude.
Since if it were not so, [if its sensible qualities were not
divisible, pari passu with body], we might conceive a body existing
but having no colour, or weight, or any such quality; accordingly
not perceptible at all. For these qualities are the objects of
sense-perception. On this supposition, every perceptible object should
be regarded as composed not of perceptible [but of imperceptible]
parts. Yet it must [be really composed of perceptible parts], since
assuredly it does not consist of mathematical [and therefore purely
abstract and non-sensible] quantities. Again, by what faculty should
we discern and cognize these [hypothetical real things without
sensible qualities]? Is it by Reason? But they are not objects of
Reason; nor does reason apprehend objects in space, except when it
acts in conjunction with sense-perception. At the same time, if this
be the case [that there are magnitudes, physically real, but without
sensible quality], it seems to tell in favour of the atomistic
hypothesis; for thus, indeed, [by accepting this hypothesis], the
question [with which this chapter begins] might be solved
[negatively]. But it is impossible [to accept this hypothesis]. Our
views on the subject of atoms are to be found in our treatise on
The solution of these questions will bring with it also the answer
to the question why the species of Colour, Taste, Sound, and other
sensible qualities are limited. For in all classes of things lying
between extremes the intermediates must be limited. But contraries are
extremes, and every object of sense-perception involves contrariety:
e.g. in Colour, White x Black; in Savour, Sweet x Bitter, and in all
the other sensibles also the contraries are extremes. Now, that
which is continuous is divisible into an infinite number of unequal
parts, but into a finite number of equal parts, while that which is
not per se continuous is divisible into species which are finite in
number. Since then, the several sensible qualities of things are to be
reckoned as species, while continuity always subsists in these, we
must take account of the difference between the Potential and the
Actual. It is owing to this difference that we do not [actually] see
its ten-thousandth part in a grain of millet, although sight has
embraced the whole grain within its scope; and it is owing to this,
too, that the sound contained in a quarter-tone escapes notice, and
yet one hears the whole strain, inasmuch as it is a continuum; but the
interval between the extreme sounds [that bound the quarter-tone]
escapes the ear [being only potentially audible, not actually]. So, in
the case of other objects of sense, extremely small constituents are
unnoticed; because they are only potentially not actually [perceptible
e.g.] visible, unless when they have been parted from the wholes. So
the footlength too exists potentially in the two-foot length, but
actually only when it has been separated from the whole. But objective
increments so small as those above might well, if separated from their
totals, [instead of achieving 'actual' exisistence] be dissolved in
their environments, like a drop of sapid moisture poured out into
the sea. But even if this were not so [sc. with the objective
magnitude], still, since the [subjective] of sense-perception is not
perceptible in itself, nor capable of separate existence (since it
exists only potentially in the more distinctly perceivable whole of
sense-perception), so neither will it be possible to perceive
[actually] its correlatively small object [sc. its quantum of
pathema or sensible quality] when separated from the object-total. But
yet this [small object] is to be considered as perceptible: for it
is both potentially so already [i.e. even when alone], and destined to
be actually so when it has become part of an aggregate. Thus,
therefore, we have shown that some magnitudes and their sensible
qualities escape notice, and the reason why they do so, as well as the
manner in which they are still perceptible or not perceptible in
such cases. Accordingly then when these [minutely subdivided]
sensibles have once again become aggregated in a whole in such a
manner, relatively to one another, as to be perceptible actually,
and not merely because they are in the whole, but even apart from
it, it follows necessarily [from what has been already stated] that
their sensible qualities, whether colours or tastes or sounds, are
limited in number.
One might ask:- do the objects of sense-perception, or the
movements proceeding from them ([since movements there are,] in
whichever of the two ways [viz. by emanations or by stimulatory
kinesis] sense-perception takes place), when these are actualized
for perception, always arrive first at a spatial middle point [between
the sense-organ and its object], as Odour evidently does, and also
Sound? For he who is nearer [to the odorous object] perceives the
Odour sooner [than who is farther away], and the Sound of a stroke
reaches us some time after it has been struck. Is it thus also with an
object seen, and with Light? Empedocles, for example, says that the
Light from the Sun arrives first in the intervening space before it
comes to the eye, or reaches the Earth. This might plausibly seem to
be the case. For whatever is moved [in space], is moved from one place
to another; hence there must be a corresponding interval of time
also in which it is moved from the one place to the other. But any
given time is divisible into parts; so that we should assume a time
when the sun's ray was not as yet seen, but was still travelling in
the middle space.
Now, even if it be true that the acts of 'hearing' and 'having
heard', and, generally, those of 'perceiving' and 'having
perceived', form co-instantaneous wholes, in other words, that acts of
sense-perception do not involve a process of becoming, but have
their being none the less without involving such a process; yet,
just as, [in the case of sound], though the stroke which causes the
Sound has been already struck, the Sound is not yet at the ear (and
that this last is a fact is further proved by the transformation which
the letters [viz. the consonants as heard] undergo [in the case of
words spoken from a distance], implying that the local movement
[involved in Sound] takes place in the space between [us and the
speaker]; for the reason why [persons addressed from a distance] do
not succeed in catching the sense of what is said is evidently that
the air [sound wave] in moving towards them has its form changed)
[granting this, then, the question arises]: is the same also true in
the case of Colour and Light? For certainly it is not true that the
beholder sees, and the object is seen, in virtue of some merely
abstract relationship between them, such as that between equals. For
if it were so, there would be no need [as there is] that either [the
beholder or the thing beheld] should occupy some particular place;
since to the equalization of things their being near to, or far
from, one another makes no difference.
Now this [travelling through successive positions in the medium] may
with good reason take place as regards Sound and Odour, for these,
like [their media] Air and Water, are continuous, but the movement
of both is divided into parts. This too is the ground of the fact that
the object which the person first in order of proximity hears or
smells is the same as that which each subsequent person perceives,
while yet it is not the same.
Some, indeed, raise a question also on these very points; they
declare it impossible that one person should hear, or see, or smell,
the same object as another, urging the impossibility of several
persons in different places hearing or smelling [the same object], for
the one same thing would [thus] be divided from itself. The answer
is that, in perceiving the object which first set up the motion- e.g.
a bell, or frankincense, or fire- all perceive an object numerically
one and the same; while, of course, in the special object perceived
they perceive an object numerically different for each, though
specifically the same for all; and this, accordingly, explains how it
is that many persons together see, or smell, or hear [the same
object]. These things [the odour or sound proper] are not bodies, but
an affection or process of some kind (otherwise this [viz.
simultaneous perception of the one object by many] would not have
been, as it is, a fact of experience) though, on the other hand, they
each imply a body [as their cause].
But [though sound and odour may travel,] with regard to Light the
case is different. For Light has its raison d'etre in the being [not
becoming] of something, but it is not a movement. And in general, even
in qualitative change the case is different from what it is in local
movement [both being different species of kinesis]. Local movements,
of course, arrive first at a point midway before reaching their goal
(and Sound, it is currently believed, is a movement of something
locally moved), but we cannot go on to assert this [arrival at a point
midway] like manner of things which undergo qualitative change. For
this kind of change may conceivably take place in a thing all at once,
without one half of it being changed before the other; e.g. it is
conceivable that water should be frozen simultaneously in every
part. But still, for all that, if the body which is heated or frozen
is extensive, each part of it successively is affected by the part
contiguous, while the part first changed in quality is so changed by
the cause itself which originates the change, and thus the change
throughout the whole need not take place coinstantaneously and all
at once. Tasting would have been as smelling now is, if we lived in
a liquid medium, and perceived [the sapid object] at a distance,
before touching it.
Naturally, then, the parts of media between a sensory organ and
its object are not all affected at once- except in the case of Light
[illumination] for the reason above stated, and also in the case of
seeing, for the same reason; for Light is an efficient cause of

Another question respecting sense-perception is as follows:
assuming, as is natural, that of two [simultaneous] sensory stimuli
the stronger always tends to extrude the weaker [from
consciousness], is it conceivable or not that one should be able to
discern two objects coinstantaneously in the same individual time? The
above assumption explains why persons do not perceive what is
brought before their eyes, if they are at the time deep in thought, or
in a fright, or listening to some loud noise. This assumption, then,
must be made, and also the following: that it is easier to discern
each object of sense when in its simple form than when an ingredient
in a mixture; easier, for example, to discern wine when neat than when
blended, and so also honey, and [in other provinces] a colour, or to
discern the nete by itself alone, than [when sounded with the
hypate] in the octave; the reason being that component elements tend
to efface [the distinctive characteristics of] one another. Such is
the effect [on one another] of all ingredients of which, when
compounded, some one thing is formed.
If, then, the greater stimulus tends to expel the less, it
necessarily follows that, when they concur, this greater should itself
too be less distinctly perceptible than if it were alone, since the
less by blending with it has removed some of its individuality,
according to our assumption that simple objects are in all cases
more distinctly perceptible.
Now, if the two stimuli are equal but heterogeneous, no perception
of either will ensue; they will alike efface one another's
characteristics. But in such a case the perception of either
stimulus in its simple form is impossible. Hence either there will
then be no sense-perception at all, or there will be a perception
compounded of both and differing from either. The latter is what
actually seems to result from ingredients blended together, whatever
may be the compound in which they are so mixed.
Since, then, from some concurrent [sensory stimuli] a resultant
object is produced, while from others no such resultant is produced,
and of the latter sort are those things which belong to different
sense provinces (for only those things are capable of mixture whose
extremes are contraries, and no one compound can be formed from,
e.g. White and Sharp, except indirectly, i.e. not as a concord is
formed of Sharp and Grave); there follows logically the
impossibility of discerning such concurrent stimuli coinstantaneously.
For we must suppose that the stimuli, when equal, tend alike to efface
one another, since no one [form of stimulus] results from them; while,
if they are unequal, the stronger alone is distinctly perceptible.
Again, the soul would be more likely to perceive
coinstantaneously, with one and the same sensory act, two things in
the same sensory province, such as the Grave and the Sharp in sound;
for the sensory stimulation in this one province is more likely to
be unitemporal than that involving two different provinces, as Sight
and Hearing. But it is impossible to perceive two objects
coinstantaneously in the same sensory act unless they have been mixed,
[when, however, they are no longer two], for their amalgamation
involves their becoming one, and the sensory act related to one object
is itself one, and such act, when one, is, of course,
coinstantaneous with itself. Hence, when things are mixed we of
necessity perceive them coinstantaneously: for we perceive them by a
perception actually one. For an object numerically one means that
which is perceived by a perception actually one, whereas an object
specifically one means that which is perceived by a sensory act
potentially one [i.e. by an energeia of the same sensuous faculty]. If
then the actualized perception is one, it will declare its data to
be one object; they must, therefore, have been mixed. Accordingly,
when they have not been mixed, the actualized perceptions which
perceive them will be two; but [if so, their perception must be
successive not coinstantaneous, for] in one and the same faculty the
perception actualized at any single moment is necessarily one, only
one stimulation or exertion of a single faculty being possible at a
single instant, and in the case supposed here the faculty is one. It
follows, therefore, that we cannot conceive the possibility of
perceiving two distinct objects coinstantaneously with one and the
same sense.
But if it be thus impossible to perceive coinstantaneously two
objects in the same province of sense if they are really two,
manifestly it is still less conceivable that we should perceive
coinstantaneously objects in two different sensory provinces, as White
and Sweet. For it appears that when the Soul predicates numerical
unity it does so in virtue of nothing else than such coinstantaneous
perception [of one object, in one instant, by one energeia]: while
it predicates specific unity in virtue of [the unity of] the
discriminating faculty of sense together with [the unity of] the
mode in which this operates. What I mean, for example, is this; the
same sense no doubt discerns White and Black, [which are hence
generically one] though specifically different from one another, and
so, too, a faculty of sense self-identical, but different from the
former, discerns Sweet and Bitter; but while both these faculties
differ from one another [and each from itself] in their modes of
discerning either of their respective contraries, yet in perceiving
the co-ordinates in each province they proceed in manners analogous to
one another; for instance, as Taste perceives Sweet, so Sight
perceives White; and as the latter perceives Black, so the former
perceives Bitter.
Again, if the stimuli of sense derived from Contraries are
themselves Contrary, and if Contraries cannot be conceived as
subsisting together in the same individual subject, and if Contraries,
e.g. Sweet and Bitter, come under one and the same sense-faculty, we
must conclude that it is impossible to discern them coinstantaneously.
It is likewise clearly impossible so to discern such homogeneous
sensibles as are not [indeed] Contrary, [but are yet of different
species]. For these are, [in the sphere of colour, for instance],
classed some with White, others with Black, and so it is, likewise, in
the other provinces of sense; for example, of savours, some are
classed with Sweet, and others with Bitter. Nor can one discern the
components in compounds coinstantaneously (for these are ratios of
Contraries, as e.g. the Octave or the Fifth); unless, indeed, on
condition of perceiving them as one. For thus, and not otherwise,
the ratios of the extreme sounds are compounded into one ratio:
since we should have together the ratio, on the one hand, of Many to
Few or of Odd to Even, on the other, that of Few to Many or of Even to
Odd [and these, to be perceived together, must be unified].
If, then, the sensibles denominated co-ordinates though in different
provinces of sense (e.g. I call Sweet and White co-ordinates though in
different provinces) stand yet more aloof, and differ more, from one
another than do any sensibles in the same province; while Sweet
differs from White even more than Black does from White, it is still
less conceivable that one should discern them [viz. sensibles in
different sensory provinces whether co-ordinates or not]
coinstantaneously than sensibles which are in the same province.
Therefore, if coinstantaneous perception of the latter be
impossible, that of the former is a fortiori impossible.
Some of the writers who treat of concords assert that the sounds
combined in these do not reach us simultaneously, but only appear to
do so, their real successiveness being unnoticed whenever the time
it involves is [so small as to be] imperceptible. Is this true or not?
One might perhaps, following this up, go so far as to say that even
the current opinion that one sees and hears coinstantaneously is due
merely to the fact that the intervals of time [between the really
successive perceptions of sight and hearing] escape observation. But
this can scarcely be true, nor is it conceivable that any portion of
time should be [absolutely] imperceptible, or that any should be
absolutely unnoticeable; the truth being that it is possible to
perceive every instant of time. [This is so]; because, if it is
inconceivable that a person should, while perceiving himself or
aught else in a continuous time, be at any instant unaware of his
own existence; while, obviously, the assumption, that there is in
the time-continuum a time so small as to be absolutely
imperceptible, carries the implication that a person would, during
such time, be unaware of his own existence, as well as of his seeing
and perceiving; [this assumption must be false].
Again, if there is any magnitude, whether time or thing,
absolutely imperceptible owing to its smallness, it follows that there
would not be either a thing which one perceives, or a time in which
one perceives it, unless in the sense that in some part of the given
time he sees some part of the given thing. For [let there be a line
ab, divided into two parts at g, and let this line represent a whole
object and a corresponding whole time. Now,] if one sees the whole
line, and perceives it during a time which forms one and the same
continuum, only in the sense that he does so in some portion of this
time, let us suppose the part gb, representing a time in which by
supposition he was perceiving nothing, cut off from the whole. Well,
then, he perceives in a certain part [viz. in the remainder] of the
time, or perceives a part [viz. the remainder] of the line, after
the fashion in which one sees the whole earth by seeing some given
part of it, or walks in a year by walking in some given part of the
year. But [by hypothesis] in the part bg he perceives nothing:
therefore, in fact, he is said to perceive the whole object and during
the whole time simply because he perceives [some part of the object]
in some part of the time ab. But the same argument holds also in the
case of ag [the remainder, regarded in its turn as a whole]; for it
will be found [on this theory of vacant times and imperceptible
magnitudes] that one always perceives only in some part of a given
whole time, and perceives only some part of a whole magnitude, and
that it is impossible to perceive any [really] whole [object in a
really whole time; a conclusion which is absurd, as it would logically
annihilate the perception of both Objects and Time].
Therefore we must conclude that all magnitudes are perceptible,
but their actual dimensions do not present themselves immediately in
their presentation as objects. One sees the sun, or a four-cubit rod
at a distance, as a magnitude, but their exact dimensions are not
given in their visual presentation: nay, at times an object of sight
appears indivisible, but [vision like other special senses, is
fallible respecting 'common sensibles', e.g. magnitude, and] nothing
that one sees is really indivisible. The reason of this has been
previously explained. It is clear then, from the above arguments, that
no portion of time is imperceptible.
But we must here return to the question proposed above for
discussion, whether it is possible or impossible to perceive several
objects coinstantaneously; by 'coinstantaneously' I mean perceiving
the several objects in a time one and indivisible relatively to one
another, i.e. indivisible in a sense consistent with its being all a
First, then, is it conceivable that one should perceive the
different things coinstantaneously, but each with a different part
of the Soul? Or [must we object] that, in the first place, to begin
with the objects of one and the same sense, e.g. Sight, if we assume
it [the Soul qua exercising Sight] to perceive one colour with one
part, and another colour with a different part, it will have a
plurality of parts the same in species, [as they must be,] since the
objects which it thus perceives fall within the same genus?
Should any one [to illustrate how the Soul might have in it two
different parts specifically identical, each directed to a set of
aistheta the same in genus with that to which the other is directed]
urge that, as there are two eyes, so there may be in the Soul
something analogous, [the reply is] that of the eyes, doubtless,
some one organ is formed, and hence their actualization in
perception is one; but if this is so in the Soul, then, in so far as
what is formed of both [i.e. of any two specifically identical parts
as assumed] is one, the true perceiving subject also will be one, [and
the contradictory of the above hypothesis (of different parts of
Soul remaining engaged in simultaneous perception with one sense) is
what emerges from the analogy]; while if the two parts of Soul
remain separate, the analogy of the eyes will fail, [for of these some
one is really formed].
Furthermore, [on the supposition of the need of different parts of
Soul, co-operating in each sense, to discern different objects
coinstantaneously], the senses will be each at the same time one and
many, as if we should say that they were each a set of diverse
sciences; for neither will an 'activity' exist without its proper
faculty, nor without activity will there be sensation.
But if the Soul does not, in the way suggested [i.e. with
different parts of itself acting simultaneously], perceive in one
and the same individual time sensibles of the same sense, a fortiori
it is not thus that it perceives sensibles of different senses. For it
is, as already stated, more conceivable that it should perceive a
plurality of the former together in this way than a plurality of
heterogeneous objects.
If then, as is the fact, the Soul with one part perceives Sweet,
with another, White, either that which results from these is some
one part, or else there is no such one resultant. But there must be
such an one, inasmuch as the general faculty of sense-perception is
one. What one object, then, does that one faculty [when perceiving
an object, e.g. as both White and Sweet] perceive? [None]; for
assuredly no one object arises by composition of these
[heterogeneous objects, such as White and Sweet]. We must conclude,
therefore, that there is, as has been stated before, some one
faculty in the soul with which the latter perceives all its
percepts, though it perceives each different genus of sensibles
through a different organ.
May we not, then, conceive this faculty which perceives White and
Sweet to be one qua indivisible [sc. qua combining its different
simultaneous objects] in its actualization, but different, when it has
become divisible [sc. qua distinguishing its different simultaneous
objects] in its actualization?
Or is what occurs in the case of the perceiving Soul conceivably
analogous to what holds true in that of the things themselves? For the
same numerically one thing is white and sweet, and has many other
qualities, [while its numerical oneness is not thereby prejudiced]
if the fact is not that the qualities are really separable in the
object from one another, but that the being of each quality is
different [from that of every other]. In the same way therefore we
must assume also, in the case of the Soul, that the faculty of
perception in general is in itself numerically one and the same, but
different [differentiated] in its being; different, that is to say, in
genus as regards some of its objects, in species as regards others.
Hence too, we may conclude that one can perceive [numerically
different objects] coinstantaneously with a faculty which is
numerically one and the same, but not the same in its relationship
[sc. according as the objects to which it is directed are not the
That every sensible object is a magnitude, and that nothing which it
is possible to perceive is indivisible, may be thus shown. The
distance whence an object could not be seen is indeterminate, but that
whence it is visible is determinate. We may say the same of the
objects of Smelling and Hearing, and of all sensibles not discerned by
actual contact. Now, there is, in the interval of distance, some
extreme place, the last from which the object is invisible, and the
first from which it is visible. This place, beyond which if the object
be one cannot perceive it, while if the object be on the hither side
one must perceive it, is, I presume, itself necessarily indivisible.
Therefore, if any sensible object be indivisible, such object, if
set in the said extreme place whence imperceptibility ends and
perceptibility begins, will have to be both visible and invisible
their objects, whether regarded in general or at the same time; but
this is impossible.
This concludes our survey of the characteristics of the organs of
Sense-perception and their objects, whether regarded in general or
in relation to each organ. Of the remaining subjects, we must first
consider that of memory and remembering.



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