ON THE SOUL...................................................................................................................................................1

by Aristotle..............................................................................................................................................1

Book I.....................................................................................................................................................1

Book II..................................................................................................................................................13

Book III .................................................................................................................................................28

HOLDING as we do that, while knowledge of any kind is a thing to be honoured and prized, one kind of it

may, either by reason of its greater exactness or of a higher dignity and greater wonderfulness in its objects,

be more honourable and precious than another, on both accounts we should naturally be led to place in the

front rank the study of the soul. The knowledge of the soul admittedly contributes greatly to the advance of

truth in general, and, above all, to our understanding of Nature, for the soul is in some sense the principle of

animal life. Our aim is to grasp and understand, first its essential nature, and secondly its properties; of these

some are taught to be affections proper to the soul itself, while others are considered to attach to the animal

To attain any assured knowledge about the soul is one of the most difficult things in the world. As the form of

question which here presents itself, viz. the question 'What is it?', recurs in other fields, it might be supposed

that there was some single method of inquiry applicable to all objects whose essential nature (as we are

endeavouring to ascertain there is for derived properties the single method of demonstration); in that case

what we should have to seek for would be this unique method. But if there is no such single and general

method for solving the question of essence, our task becomes still more difficult; in the case of each different

subject we shall have to determine the appropriate process of investigation. If to this there be a clear answer,

e.g. that the process is demonstration or division, or some known method, difficulties and hesitations still

beset uswith what facts shall we begin the inquiry? For the facts which form the startingpoints in different

First, no doubt, it is necessary to determine in which of the summa genera soul lies, what it is; is it 'a

thissomewhat, 'a substance, or is it a quale or a quantum, or some other of the remaining kinds of predicates

which we have distinguished? Further, does soul belong to the class of potential existents, or is it not rather

We must consider also whether soul is divisible or is without parts, and whether it is everywhere

homogeneous or not; and if not homogeneous, whether its various forms are different specifically or

generically: up to the present time those who have discussed and investigated soul seem to have confined

themselves to the human soul. We must be careful not to ignore the question whether soul can be defined in a

single unambiguous formula, as is the case with animal, or whether we must not give a separate formula for

each of it, as we do for horse, dog, man, god (in the latter case the 'universal' animaland so too every other

'common predicate'being treated either as nothing at all or as a later product). Further, if what exists is not a

plurality of souls, but a plurality of parts of one soul, which ought we to investigate first, the whole soul or its

parts? (It is also a difficult problem to decide which of these parts are in nature distinct from one another.)

Again, which ought we to investigate first, these parts or their functions, mind or thinking, the faculty or the

act of sensation, and so on? If the investigation of the functions precedes that of the parts, the further question

suggests itself: ought we not before either to consider the correlative objects, e.g. of sense or thought? It

seems not only useful for the discovery of the causes of the derived properties of substances to be acquainted

with the essential nature of those substances (as in mathematics it is useful for the understanding of the

property of the equality of the interior angles of a triangle to two right angles to know the essential nature of

the straight and the curved or of the line and the plane) but also conversely, for the knowledge of the essential

nature of a substance is largely promoted by an acquaintance with its properties: for, when we are able to give

an account conformable to experience of all or most of the properties of a substance, we shall be in the most

favourable position to say something worth saying about the essential nature of that subject; in all

demonstration a definition of the essence is required as a startingpoint, so that definitions which do not

enable us to discover the derived properties, or which fail to facilitate even a conjecture about them, must

A further problem presented by the affections of soul is this: are they all affections of the complex of body

and soul, or is there any one among them peculiar to the soul by itself? To determine this is indispensable but

difficult. If we consider the majority of them, there seems to be no case in which the soul can act or be acted

upon without involving the body; e.g. anger, courage, appetite, and sensation generally. Thinking seems the

most probable exception; but if this too proves to be a form of imagination or to be impossible without

imagination, it too requires a body as a condition of its existence. If there is any way of acting or being acted

upon proper to soul, soul will be capable of separate existence; if there is none, its separate existence is

impossible. In the latter case, it will be like what is straight, which has many properties arising from the

straightness in it, e.g. that of touching a bronze sphere at a point, though straightness divorced from the other

constituents of the straight thing cannot touch it in this way; it cannot be so divorced at all, since it is always

found in a body. It therefore seems that all the affections of soul involve a bodypassion, gentleness, fear,

pity, courage, joy, loving, and hating; in all these there is a concurrent affection of the body. In support of this

we may point to the fact that, while sometimes on the occasion of violent and striking occurrences there is no

excitement or fear felt, on others faint and feeble stimulations produce these emotions, viz. when the body is

already in a state of tension resembling its condition when we are angry. Here is a still clearer case: in the

absence of any external cause of terror we find ourselves experiencing the feelings of a man in terror. From

all this it is obvious that the affections of soul are enmattered formulable essences.

Consequently their definitions ought to correspond, e.g. anger should be defined as a certain mode of

movement of such and such a body (or part or faculty of a body) by this or that cause and for this or that end.

That is precisely why the study of the soul must fall within the science of Nature, at least so far as in its

affections it manifests this double character. Hence a physicist would define an affection of soul differently

from a dialectician; the latter would define e.g. anger as the appetite for returning pain for pain, or something

like that, while the former would define it as a boiling of the blood or warm substance surround the heart. The

latter assigns the material conditions, the former the form or formulable essence; for what he states is the

formulable essence of the fact, though for its actual existence there must be embodiment of it in a material

such as is described by the other. Thus the essence of a house is assigned in such a formula as 'a shelter

against destruction by wind, rain, and heat'; the physicist would describe it as 'stones, bricks, and timbers'; but

there is a third possible description which would say that it was that form in that material with that purpose or

end. Which, then, among these is entitled to be regarded as the genuine physicist? The one who confines

himself to the material, or the one who restricts himself to the formulable essence alone? Is it not rather the

one who combines both in a single formula? If this is so, how are we to characterize the other two? Must we

not say that there is no type of thinker who concerns himself with those qualities or attributes of the material

which are in fact inseparable from the material, and without attempting even in thought to separate them? The

physicist is he who concerns himself with all the properties active and passive of bodies or materials thus or

thus defined; attributes not considered as being of this character he leaves to others, in certain cases it may be

to a specialist, e.g. a carpenter or a physician, in others (a) where they are inseparable in fact, but are

separable from any particular kind of body by an effort of abstraction, to the mathematician, (b) where they

are separate both in fact and in thought from body altogether, to the First Philosopher or metaphysician. But

we must return from this digression, and repeat that the affections of soul are inseparable from the material

substratum of animal life, to which we have seen that such affections, e.g. passion and fear, attach, and have

For our study of soul it is necessary, while formulating the problems of which in our further advance we are

to find the solutions, to call into council the views of those of our predecessors who have declared any

opinion on this subject, in order that we may profit by whatever is sound in their suggestions and avoid their

The startingpoint of our inquiry is an exposition of those characteristics which have chiefly been held to

belong to soul in its very nature. Two characteristic marks have above all others been recognized as

distinguishing that which has soul in it from that which has notmovement and sensation. It may be said that

Some say that what originates movement is both preeminently and primarily soul; believing that what is not

itself moved cannot originate movement in another, they arrived at the view that soul belongs to the class of

things in movement. This is what led Democritus to say that soul is a sort of fire or hot substance; his 'forms'

or atoms are infinite in number; those which are spherical he calls fire and soul, and compares them to the

motes in the air which we see in shafts of light coming through windows; the mixture of seeds of all sorts he

calls the elements of the whole of Nature (Leucippus gives a similar account); the spherical atoms are

identified with soul because atoms of that shape are most adapted to permeate everywhere, and to set all the

others moving by being themselves in movement. This implies the view that soul is identical with what

produces movement in animals. That is why, further, they regard respiration as the characteristic mark of life;

as the environment compresses the bodies of animals, and tends to extrude those atoms which impart

movement to them, because they themselves are never at rest, there must be a reinforcement of these by

similar atoms coming in from without in the act of respiration; for they prevent the extrusion of those which

are already within by counteracting the compressing and consolidating force of the environment; and animals

The doctrine of the Pythagoreans seems to rest upon the same ideas; some of them declared the motes in air,

others what moved them, to be soul. These motes were referred to because they are seen always in

The same tendency is shown by those who define soul as that which moves itself; all seem to hold the view

that movement is what is closest to the nature of soul, and that while all else is moved by soul, it alone moves

itself. This belief arises from their never seeing anything originating movement which is not first itself

Similarly also Anaxagoras (and whoever agrees with him in saying that mind set the whole in movement)

declares the moving cause of things to be soul. His position must, however, be distinguished from that of

Democritus. Democritus roundly identifies soul and mind, for he identifies what appears with what is

truethat is why he commends Homer for the phrase 'Hector lay with thought distraught'; he does not employ

mind as a special faculty dealing with truth, but identifies soul and mind. What Anaxagoras says about them

is more obscure; in many places he tells us that the cause of beauty and order is mind, elsewhere that it is

soul; it is found, he says, in all animals, great and small, high and low, but mind (in the sense of intelligence)

appears not to belong alike to all animals, and indeed not even to all human beings.

All those, then, who had special regard to the fact that what has soul in it is moved, adopted the view that

soul is to be identified with what is eminently originative of movement. All, on the other hand, who looked to

the fact that what has soul in it knows or perceives what is, identify soul with the principle or principles of

Nature, according as they admit several such principles or one only. Thus Empedocles declares that it is

In the same way Plato in the Timaeus fashions soul out of his elements; for like, he holds, is known by like,

and things are formed out of the principles or elements, so that soul must be so too. Similarly also in his

lectures 'On Philosophy' it was set forth that the Animalitself is compounded of the Idea itself of the One

together with the primary length, breadth, and depth, everything else, the objects of its perception, being

similarly constituted. Again he puts his view in yet other terms: Mind is the monad, science or knowledge the

dyad (because it goes undeviatingly from one point to another), opinion the number of the plane, sensation

the number of the solid; the numbers are by him expressly identified with the Forms themselves or principles,

and are formed out of the elements; now things are apprehended either by mind or science or opinion or

Some thinkers, accepting both premisses, viz. that the soul is both originative of movement and cognitive,

As to the nature and number of the first principles opinions differ. The difference is greatest between those

who regard them as corporeal and those who regard them as incorporeal, and from both dissent those who

make a blend and draw their principles from both sources. The number of principles is also in dispute; some

admit one only, others assert several. There is a consequent diversity in their several accounts of soul; they

assume, naturally enough, that what is in its own nature originative of movement must be among what is

primordial. That has led some to regard it as fire, for fire is the subtlest of the elements and nearest to

incorporeality; further, in the most primary sense, fire both is moved and originates movement in all the

Democritus has expressed himself more ingeniously than the rest on the grounds for ascribing each of these

two characters to soul; soul and mind are, he says, one and the same thing, and this thing must be one of the

primary and indivisible bodies, and its power of originating movement must be due to its fineness of grain

and the shape of its atoms; he says that of all the shapes the spherical is the most mobile, and that this is the

Anaxagoras, as we said above, seems to distinguish between soul and mind, but in practice he treats them as a

single substance, except that it is mind that he specially posits as the principle of all things; at any rate what

he says is that mind alone of all that is simple, unmixed, and pure. He assigns both characteristics, knowing

and origination of movement, to the same principle, when he says that it was mind that set the whole in

Thales, too, to judge from what is recorded about him, seems to have held soul to be a motive force, since he

Diogenes (and others) held the soul to be air because he believed air to be finest in grain and a first principle;

therein lay the grounds of the soul's powers of knowing and originating movement. As the primordial

principle from which all other things are derived, it is cognitive; as finest in grain, it has the power to

Heraclitus too says that the first principlethe 'warm exhalation' of which, according to him, everything else

is composedis soul; further, that this exhalation is most incorporeal and in ceaseless flux; that what is in

movement requires that what knows it should be in movement; and that all that is has its being essentially in

Alcmaeon also seems to have held a similar view about soul; he says that it is immortal because it resembles

'the immortals,' and that this immortality belongs to it in virtue of its ceaseless movement; for all the 'things

divine,' moon, sun, the planets, and the whole heavens, are in perpetual movement.

of More superficial writers, some, e.g. Hippo, have pronounced it to be water; they seem to have argued from

the fact that the seed of all animals is fluid, for Hippo tries to refute those who say that the soul is blood, on

Another group (Critias, for example) did hold it to be blood; they take perception to be the most characteristic

Each of the elements has thus found its partisan, except earthearth has found no supporter unless we count

as such those who have declared soul to be, or to be compounded of, all the elements. All, then, it may be

said, characterize the soul by three marks, Movement, Sensation, Incorporeality, and each of these is traced

back to the first principles. That is why (with one exception) all those who define the soul by its power of

knowing make it either an element or constructed out of the elements. The language they all use is similar;

like, they say, is known by like; as the soul knows everything, they construct it out of all the principles.

Hence all those who admit but one cause or element, make the soul also one (e.g. fire or air), while those who

admit a multiplicity of principles make the soul also multiple. The exception is Anaxagoras; he alone says

that mind is impassible and has nothing in common with anything else. But, if this is so, how or in virtue of

what cause can it know? That Anaxagoras has not explained, nor can any answer be inferred from his words.

All who acknowledge pairs of opposites among their principles, construct the soul also out of these

contraries, while those who admit as principles only one contrary of each pair, e.g. either hot or cold, likewise

make the soul some one of these. That is why, also, they allow themselves to be guided by the names; those

who identify soul with the hot argue that sen (to live) is derived from sein (to boil), while those who identify

it with the cold say that soul (psuche) is so called from the process of respiration and (katapsuxis). Such are

the traditional opinions concerning soul, together with the grounds on which they are maintained.

We must begin our examination with movement; for doubtless, not only is it false that the essence of soul is

correctly described by those who say that it is what moves (or is capable of moving) itself, but it is an

We have already pointed out that there is no necessity that what originates movement should itself be moved.

There are two senses in which anything may be movedeither (a) indirectly, owing to something other than

itself, or (b) directly, owing to itself. Things are 'indirectly moved' which are moved as being contained in

something which is moved, e.g. sailors in a ship, for they are moved in a different sense from that in which

the ship is moved; the ship is 'directly moved', they are 'indirectly moved', because they are in a moving

vessel. This is clear if we consider their limbs; the movement proper to the legs (and so to man) is walking,

and in this case the sailors tare not walking. Recognizing the double sense of 'being moved', what we have to

consider now is whether the soul is 'directly moved' and participates in such direct movement.

There are four species of movementlocomotion, alteration, diminution, growth; consequently if the soul is

moved, it must be moved with one or several or all of these species of movement. Now if its movement is not

incidental, there must be a movement natural to it, and, if so, as all the species enumerated involve place,

place must be natural to it. But if the essence of soul be to move itself, its being moved cannot be incidental

toas it is to what is white or three cubits long; they too can be moved, but only incidentallywhat is moved

is that of which 'white' and 'three cubits long' are the attributes, the body in which they inhere; hence they

have no place: but if the soul naturally partakes in movement, it follows that it must have a place.

Further, if there be a movement natural to the soul, there must be a countermovement unnatural to it, and

conversely. The same applies to rest as well as to movement; for the terminus ad quem of a thing's natural

movement is the place of its natural rest, and similarly the terminus ad quem of its enforced movement is the

place of its enforced rest. But what meaning can be attached to enforced movements or rests of the soul, it is

Further, if the natural movement of the soul be upward, the soul must be fire; if downward, it must be earth;

for upward and downward movements are the definitory characteristics of these bodies. The same reasoning

applies to the intermediate movements, termini, and bodies. Further, since the soul is observed to originate

movement in the body, it is reasonable to suppose that it transmits to the body the movements by which it

itself is moved, and so, reversing the order, we may infer from the movements of the body back to similar

movements of the soul. Now the body is moved from place to place with movements of locomotion. Hence it

would follow that the soul too must in accordance with the body change either its place as a whole or the

relative places of its parts. This carries with it the possibility that the soul might even quit its body and

reenter it, and with this would be involved the possibility of a resurrection of animals from the dead. But, it

may be contended, the soul can be moved indirectly by something else; for an animal can be pushed out of its

course. Yes, but that to whose essence belongs the power of being moved by itself, cannot be moved by

something else except incidentally, just as what is good by or in itself cannot owe its goodness to something

If the soul is moved, the most probable view is that what moves it is sensible things.

We must note also that, if the soul moves itself, it must be the mover itself that is moved, so that it follows

that if movement is in every case a displacement of that which is in movement, in that respect in which it is

said to be moved, the movement of the soul must be a departure from its essential nature, at least if its

Some go so far as to hold that the movements which the soul imparts to the body in which it is are the same

in kind as those with which it itself is moved. An example of this is Democritus, who uses language like that

of the comic dramatist Philippus, who accounts for the movements that Daedalus imparted to his wooden

Aphrodite by saying that he poured quicksilver into it; similarly Democritus says that the spherical atoms

which according to him constitute soul, owing to their own ceaseless movements draw the whole body after

them and so produce its movements. We must urge the question whether it is these very same atoms which

produce rest alsohow they could do so, it is difficult and even impossible to say. And, in general, we may

object that it is not in this way that the soul appears to originate movement in animalsit is through intention

It is in the same fashion that the Timaeus also tries to give a physical account of how the soul moves its body;

the soul, it is there said, is in movement, and so owing to their mutual implication moves the body also. After

compounding the soulsubstance out of the elements and dividing it in accordance with the harmonic

numbers, in order that it may possess a connate sensibility for 'harmony' and that the whole may move in

movements well attuned, the Demiurge bent the straight line into a circle; this single circle he divided into

two circles united at two common points; one of these he subdivided into seven circles. All this implies that

the movements of the soul are identified with the local movements of the heavens.

Now, in the first place, it is a mistake to say that the soul is a spatial magnitude. It is evident that Plato means

the soul of the whole to be like the sort of soul which is called mind not like the sensitive or the desiderative

soul, for the movements of neither of these are circular. Now mind is one and continuous in the sense in

which the process of thinking is so, and thinking is identical with the thoughts which are its parts; these have

a serial unity like that of number, not a unity like that of a spatial magnitude. Hence mind cannot have that

kind of unity either; mind is either without parts or is continuous in some other way than that which

characterizes a spatial magnitude. How, indeed, if it were a spatial magnitude, could mind possibly think?

Will it think with any one indifferently of its parts? In this case, the 'part' must be understood either in the

sense of a spatial magnitude or in the sense of a point (if a point can be called a part of a spatial magnitude).

If we accept the latter alternative, the points being infinite in number, obviously the mind can never

exhaustively traverse them; if the former, the mind must think the same thing over and over again, indeed an

infinite number of times (whereas it is manifestly possible to think a thing once only). If contact of any part

whatsoever of itself with the object is all that is required, why need mind move in a circle, or indeed possess

magnitude at all? On the other hand, if contact with the whole circle is necessary, what meaning can be given

to the contact of the parts? Further, how could what has no parts think what has parts, or what has parts think

what has none? We must identify the circle referred to with mind; for it is mind whose movement is thinking,

and it is the circle whose movement is revolution, so that if thinking is a movement of revolution, the circle

If the circular movement is eternal, there must be something which mind is always thinkingwhat can this

be? For all practical processes of thinking have limitsthey all go on for the sake of something outside the

process, and all theoretical processes come to a close in the same way as the phrases in speech which express

processes and results of thinking. Every such linguistic phrase is either definitory or demonstrative.

Demonstration has both a startingpoint and may be said to end in a conclusion or inferred result; even if the

process never reaches final completion, at any rate it never returns upon itself again to its startingpoint, it

goes on assuming a fresh middle term or a fresh extreme, and moves straight forward, but circular movement

Further, if the same revolution is repeated, mind must repeatedly think the same object.

Further, thinking has more resemblance to a coming to rest or arrest than to a movement; the same may be

It might also be urged that what is difficult and enforced is incompatible with blessedness; if the movement

of the soul is not of its essence, movement of the soul must be contrary to its nature. It must also be painful

for the soul to be inextricably bound up with the body; nay more, if, as is frequently said and widely

accepted, it is better for mind not to be embodied, the union must be for it undesirable.

Further, the cause of the revolution of the heavens is left obscure. It is not the essence of soul which is the

cause of this circular movementthat movement is only incidental to soulnor is, a fortiori, the body its

cause. Again, it is not even asserted that it is better that soul should be so moved; and yet the reason for

which God caused the soul to move in a circle can only have been that movement was better for it than rest,

and movement of this kind better than any other. But since this sort of consideration is more appropriate to

The view we have just been examining, in company with most theories about the soul, involves the following

absurdity: they all join the soul to a body, or place it in a body, without adding any specification of the reason

of their union, or of the bodily conditions required for it. Yet such explanation can scarcely be omitted; for

some community of nature is presupposed by the fact that the one acts and the other is acted upon, the one

moves and the other is moved; interaction always implies a special nature in the two interagents. All,

however, that these thinkers do is to describe the specific characteristics of the soul; they do not try to

determine anything about the body which is to contain it, as if it were possible, as in the Pythagorean myths,

that any soul could be clothed upon with any bodyan absurd view, for each body seems to have a form and

shape of its own. It is as absurd as to say that the art of carpentry could embody itself in flutes; each art must

There is yet another theory about soul, which has commended itself to many as no less probable than any of

those we have hitherto mentioned, and has rendered public account of itself in the court of popular

discussion. Its supporters say that the soul is a kind of harmony, for (a) harmony is a blend or composition of

contraries, and (b) the body is compounded out of contraries. Harmony, however, is a certain proportion or

composition of the constituents blended, and soul can be neither the one nor the other of these. Further, the

power of originating movement cannot belong to a harmony, while almost all concur in regarding this as a

principal attribute of soul. It is more appropriate to call health (or generally one of the good states of the

body) a harmony than to predicate it of the soul. The absurdity becomes most apparent when we try to

attribute the active and passive affections of the soul to a harmony; the necessary readjustment of their

conceptions is difficult. Further, in using the word 'harmony' we have one or other of two cases in our mind;

the most proper sense is in relation to spatial magnitudes which have motion and position, where harmony

means the disposition and cohesion of their parts in such a manner as to prevent the introduction into the

whole of anything homogeneous with it, and the secondary sense, derived from the former, is that in which it

means the ratio between the constituents so blended; in neither of these senses is it plausible to predicate it of

soul. That soul is a harmony in the sense of the mode of composition of the parts of the body is a view easily

refutable; for there are many composite parts and those variously compounded; of what bodily part is mind or

the sensitive or the appetitive faculty the mode of composition? And what is the mode of composition which

constitutes each of them? It is equally absurd to identify the soul with the ratio of the mixture; for the mixture

which makes flesh has a different ratio between the elements from that which makes bone. The consequence

of this view will therefore be that distributed throughout the whole body there will be many souls, since every

one of the bodily parts is a different mixture of the elements, and the ratio of mixture is in each case a

From Empedocles at any rate we might demand an answer to the following question for he says that each of

the parts of the body is what it is in virtue of a ratio between the elements: is the soul identical with this ratio,

or is it not rather something over and above this which is formed in the parts? Is love the cause of any and

every mixture, or only of those that are in the right ratio? Is love this ratio itself, or is love something over

and above this? Such are the problems raised by this account. But, on the other hand, if the soul is different

from the mixture, why does it disappear at one and the same moment with that relation between the elements

which constitutes flesh or the other parts of the animal body? Further, if the soul is not identical with the ratio

of mixture, and it is consequently not the case that each of the parts has a soul, what is that which perishes

That the soul cannot either be a harmony, or be moved in a circle, is clear from what we have said. Yet that it

can be moved incidentally is, as we said above, possible, and even that in a sense it can move itself, i.e. in the

sense that the vehicle in which it is can be moved, and moved by it; in no other sense can the soul be moved

More legitimate doubts might remain as to its movement in view of the following facts. We speak of the soul

as being pained or pleased, being bold or fearful, being angry, perceiving, thinking. All these are regarded as

modes of movement, and hence it might be inferred that the soul is moved. This, however, does not

necessarily follow. We may admit to the full that being pained or pleased, or thinking, are movements (each

of them a 'being moved'), and that the movement is originated by the soul. For example we may regard anger

or fear as such and such movements of the heart, and thinking as such and such another movement of that

organ, or of some other; these modifications may arise either from changes of place in certain parts or from

qualitative alterations (the special nature of the parts and the special modes of their changes being for our

present purpose irrelevant). Yet to say that it is the soul which is angry is as inexact as it would be to say that

it is the soul that weaves webs or builds houses. It is doubtless better to avoid saying that the soul pities or

learns or thinks and rather to say that it is the man who does this with his soul. What we mean is not that the

movement is in the soul, but that sometimes it terminates in the soul and sometimes starts from it, sensation

e.g. coming from without inwards, and reminiscence starting from the soul and terminating with the

The case of mind is different; it seems to be an independent substance implanted within the soul and to be

incapable of being destroyed. If it could be destroyed at all, it would be under the blunting influence of old

age. What really happens in respect of mind in old age is, however, exactly parallel to what happens in the

case of the sense organs; if the old man could recover the proper kind of eye, he would see just as well as the

young man. The incapacity of old age is due to an affection not of the soul but of its vehicle, as occurs in

drunkenness or disease. Thus it is that in old age the activity of mind or intellectual apprehension declines

only through the decay of some other inward part; mind itself is impassible. Thinking, loving, and hating are

affections not of mind, but of that which has mind, so far as it has it. That is why, when this vehicle decays,

memory and love cease; they were activities not of mind, but of the composite which has perished; mind is,

no doubt, something more divine and impassible. That the soul cannot be moved is therefore clear from what

we have said, and if it cannot be moved at all, manifestly it cannot be moved by itself.

Of all the opinions we have enumerated, by far the most unreasonable is that which declares the soul to be a

selfmoving number; it involves in the first place all the impossibilities which follow from regarding the soul

as moved, and in the second special absurdities which follow from calling it a number. How we to imagine a

unit being moved? By what agency? What sort of movement can be attributed to what is without parts or

internal differences? If the unit is both originative of movement and itself capable of being moved, it must

Further, since they say a moving line generates a surface and a moving point a line, the movements of the

psychic units must be lines (for a point is a unit having position, and the number of the soul is, of course,

Again, if from a number a number or a unit is subtracted, the remainder is another number; but plants and

many animals when divided continue to live, and each segment is thought to retain the same kind of soul.

It must be all the same whether we speak of units or corpuscles; for if the spherical atoms of Democritus

became points, nothing being retained but their being a quantum, there must remain in each a moving and a

moved part, just as there is in what is continuous; what happens has nothing to do with the size of the atoms,

it depends solely upon their being a quantum. That is why there must be something to originate movement in

the units. If in the animal what originates movement is the soul, so also must it be in the case of the number,

so that not the mover and the moved together, but the mover only, will be the soul. But how is it possible for

one of the units to fulfil this function of originating movement? There must be some difference between such

a unit and all the other units, and what difference can there be between one placed unit and another except a

difference of position? If then, on the other hand, these psychic units within the body are different from the

points of the body, there will be two sets of units both occupying the same place; for each unit will occupy a

point. And yet, if there can be two, why cannot there be an infinite number? For if things can occupy an

indivisible lace, they must themselves be indivisible. If, on the other hand, the points of the body are identical

with the units whose number is the soul, or if the number of the points in the body is the soul, why have not

Further, how is it possible for these points to be isolated or separated from their bodies, seeing that lines

The result is, as we have said, that this view, while on the one side identical with that of those who maintain

that soul is a subtle kind of body, is on the other entangled in the absurdity peculiar to Democritus' way of

describing the manner in which movement is originated by soul. For if the soul is present throughout the

whole percipient body, there must, if the soul be a kind of body, be two bodies in the same place; and for

those who call it a number, there must be many points at one point, or every body must have a soul, unless

the soul be a different sort of numberother, that is, than the sum of the points existing in a body. Another

consequence that follows is that the animal must be moved by its number precisely in the way that

Democritus explained its being moved by his spherical psychic atoms. What difference does it make whether

we speak of small spheres or of large units, or, quite simply, of units in movement? One way or another, the

movements of the animal must be due to their movements. Hence those who combine movement and number

in the same subject lay themselves open to these and many other similar absurdities. It is impossible not only

that these characters should give the definition of soulit is impossible that they should even be attributes of

it. The point is clear if the attempt be made to start from this as the account of soul and explain from it the

affections and actions of the soul, e.g. reasoning, sensation, pleasure, pain, For, to repeat what we have said

earlier, movement and number do not facilitate even conjecture about the derivative properties of soul.

Such are the three ways in which soul has traditionally been defined; one group of thinkers declared it to be

that which is most originative of movement because it moves itself, another group to be the subtlest and most

nearly incorporeal of all kinds of body. We have now sufficiently set forth the difficulties and inconsistencies

to which these theories are exposed. It remains now to examine the doctrine that soul is composed of the

The reason assigned for this doctrine is that thus the soul may perceive or come to know everything that is,

but the theory necessarily involves itself in many impossibilities. Its upholders assume that like is known

only by like, and imagine that by declaring the soul to be composed of the elements they succeed in

identifying the soul with all the things it is capable of apprehending. But the elements are not the only things

it knows; there are many others, or, more exactly, an infinite number of others, formed out of the elements.

Let us admit that the soul knows or perceives the elements out of which each of these composites is made up;

but by what means will it know or perceive the composite whole, e.g. what God, man, flesh, bone (or any

other compound) is? For each is, not merely the elements of which it is composed, but those elements

Nothing, therefore, will be gained by the presence of the elements in the soul, unless there be also present

there the various formulae of proportion and the various compositions in accordance with them. Each element

will indeed know its fellow outside, but there will be no knowledge of bone or man, unless they too are

present in the constitution of the soul. The impossibility of this needs no pointing out; for who would suggest

that stone or man could enter into the constitution of the soul? The same applies to 'the good' and 'the

Further, the word 'is' has many meanings: it may be used of a 'this' or substance, or of a quantum, or of a

quale, or of any other of the kinds of predicates we have distinguished. Does the soul consist of all of these or

not? It does not appear that all have common elements. Is the soul formed out of those elements alone which

enter into substances? so how will it be able to know each of the other kinds of thing? Will it be said that each

kind of thing has elements or principles of its own, and that the soul is formed out of the whole of these? In

that case, the soul must be a quantum and a quale and a substance. But all that can be made out of the

elements of a quantum is a quantum, not a substance. These (and others like them) are the consequences of

It is absurd, also, to say both (a) that like is not capable of being affected by like, and (b) that like is perceived

or known by like, for perceiving, and also both thinking and knowing, are, on their own assumption, ways of

There are many puzzles and difficulties raised by saying, as Empedocles does, that each set of things is

known by means of its corporeal elements and by reference to something in soul which is like them, and

additional testimony is furnished by this new consideration; for all the parts of the animal body which consist

wholly of earth such as bones, sinews, and hair seem to be wholly insensitive and consequently not

Further, each of the principles will have far more ignorance than knowledge, for though each of them will

know one thing, there will be many of which it will be ignorant. Empedocles at any rate must conclude that

his God is the least intelligent of all beings, for of him alone is it true that there is one thing, Strife, which he

does not know, while there is nothing which mortal beings do not know, for ere is nothing which does not

In general, we may ask, Why has not everything a soul, since everything either is an element, or is formed out

of one or several or all of the elements? Each must certainly know one or several or all.

The problem might also be raised, What is that which unifies the elements into a soul? The elements

correspond, it would appear, to the matter; what unites them, whatever it is, is the supremely important factor.

But it is impossible that there should be something superior to, and dominant over, the soul (and a fortiori

over the mind); it is reasonable to hold that mind is by nature most primordial and dominant, while their

All, both those who assert that the soul, because of its knowledge or perception of what is compounded out of

the elements, and is those who assert that it is of all things the most originative of movement, fail to take into

consideration all kinds of soul. In fact (1) not all beings that perceive can originate movement; there appear to

be certain animals which stationary, and yet local movement is the only one, so it seems, which the soul

originates in animals. And (2) the same objecton holds against all those who construct mind and the

perceptive faculty out of the elements; for it appears that plants live, and yet are not endowed with

locomotion or perception, while a large number of animals are without discourse of reason. Even if these

points were waived and mind admitted to be a part of the soul (and so too the perceptive faculty), still, even

so, there would be kinds and parts of soul of which they had failed to give any account.

The same objection lies against the view expressed in the 'Orphic' poems: there it is said that the soul comes

in from the whole when breathing takes place, being borne in upon the winds. Now this cannot take place in

the case of plants, nor indeed in the case of certain classes of animal, for not all classes of animal breathe.

If we must construct the soul out of the elements, there is no necessity to suppose that all the elements enter

into its construction; one element in each pair of contraries will suffice to enable it to know both that element

itself and its contrary. By means of the straight line we know both itself and the curvedthe carpenter's rule

enables us to test bothbut what is curved does not enable us to distinguish either itself or the straight.

Certain thinkers say that soul is intermingled in the whole universe, and it is perhaps for that reason that

Thales came to the opinion that all things are full of gods. This presents some difficulties: Why does the soul

when it resides in air or fire not form an animal, while it does so when it resides in mixtures of the elements,

and that although it is held to be of higher quality when contained in the former? (One might add the

question, why the soul in air is maintained to be higher and more immortal than that in animals.) Both

possible ways of replying to the former question lead to absurdity or paradox; for it is beyond paradox to say

that fire or air is an animal, and it is absurd to refuse the name of animal to what has soul in it. The opinion

that the elements have soul in them seems to have arisen from the doctrine that a whole must be

homogeneous with its parts. If it is true that animals become animate by drawing into themselves a portion of

what surrounds them, the partisans of this view are bound to say that the soul of the Whole too is

homogeneous with all its parts. If the air sucked in is homogeneous, but soul heterogeneous, clearly while

some part of soul will exist in the inbreathed air, some other part will not. The soul must either be

homogeneous, or such that there are some parts of the Whole in which it is not to be found.

From what has been said it is now clear that knowing as an attribute of soul cannot be explained by soul's

being composed of the elements, and that it is neither sound nor true to speak of soul as moved. But since (a)

knowing, perceiving, opining, and further (b) desiring, wishing, and generally all other modes of appetition,

belong to soul, and (c) the local movements of animals, and (d) growth, maturity, and decay are produced by

the soul, we must ask whether each of these is an attribute of the soul as a whole, i.e. whether it is with the

whole soul we think, perceive, move ourselves, act or are acted upon, or whether each of them requires a

different part of the soul? So too with regard to life. Does it depend on one of the parts of soul? Or is it

Some hold that the soul is divisible, and that one part thinks, another desires. If, then, its nature admits of its

being divided, what can it be that holds the parts together? Surely not the body; on the contrary it seems

rather to be the soul that holds the body together; at any rate when the soul departs the body disintegrates and

decays. If, then, there is something else which makes the soul one, this unifying agency would have the best

right to the name of soul, and we shall have to repeat for it the question: Is it one or multipartite? If it is one,

why not at once admit that 'the soul' is one? If it has parts, once more the question must be put: What holds its

The question might also be raised about the parts of the soul: What is the separate role of each in relation to

the body? For, if the whole soul holds together the whole body, we should expect each part of the soul to hold

together a part of the body. But this seems an impossibility; it is difficult even to imagine what sort of bodily

It is a fact of observation that plants and certain insects go on living when divided into segments; this means

that each of the segments has a soul in it identical in species, though not numerically identical in the different

segments, for both of the segments for a time possess the power of sensation and local movement. That this

does not last is not surprising, for they no longer possess the organs necessary for selfmaintenance. But, all

the same, in each of the bodily parts there are present all the parts of soul, and the souls so present are

homogeneous with one another and with the whole; this means that the several parts of the soul are

indisseverable from one another, although the whole soul is divisible. It seems also that the principle found in

plants is also a kind of soul; for this is the only principle which is common to both animals and plants; and

this exists in isolation from the principle of sensation, though there nothing which has the latter without the

LET the foregoing suffice as our account of the views concerning the soul which have been handed on by our

predecessors; let us now dismiss them and make as it were a completely fresh start, endeavouring to give a

precise answer to the question, What is soul? i.e. to formulate the most general possible definition of it.

We are in the habit of recognizing, as one determinate kind of what is, substance, and that in several senses,

(a) in the sense of matter or that which in itself is not 'a this', and (b) in the sense of form or essence, which is

that precisely in virtue of which a thing is called 'a this', and thirdly (c) in the sense of that which is

compounded of both (a) and (b). Now matter is potentiality, form actuality; of the latter there are two grades

Among substances are by general consent reckoned bodies and especially natural bodies; for they are the

principles of all other bodies. Of natural bodies some have life in them, others not; by life we mean

selfnutrition and growth (with its correlative decay). It follows that every natural body which has life in it is

But since it is also a body of such and such a kind, viz. having life, the body cannot be soul; the body is the

subject or matter, not what is attributed to it. Hence the soul must be a substance in the sense of the form of a

natural body having life potentially within it. But substance is actuality, and thus soul is the actuality of a

body as above characterized. Now the word actuality has two senses corresponding respectively to the

possession of knowledge and the actual exercise of knowledge. It is obvious that the soul is actuality in the

first sense, viz. that of knowledge as possessed, for both sleeping and waking presuppose the existence of

soul, and of these waking corresponds to actual knowing, sleeping to knowledge possessed but not employed,

and, in the history of the individual, knowledge comes before its employment or exercise.

That is why the soul is the first grade of actuality of a natural body having life potentially in it. The body so

described is a body which is organized. The parts of plants in spite of their extreme simplicity are 'organs';

e.g. the leaf serves to shelter the pericarp, the pericarp to shelter the fruit, while the roots of plants are

analogous to the mouth of animals, both serving for the absorption of food. If, then, we have to give a general

formula applicable to all kinds of soul, we must describe it as the first grade of actuality of a natural

organized body. That is why we can wholly dismiss as unnecessary the question whether the soul and the

body are one: it is as meaningless as to ask whether the wax and the shape given to it by the stamp are one, or

generally the matter of a thing and that of which it is the matter. Unity has many senses (as many as 'is' has),

but the most proper and fundamental sense of both is the relation of an actuality to that of which it is the

actuality. We have now given an answer to the question, What is soul?an answer which applies to it in its

full extent. It is substance in the sense which corresponds to the definitive formula of a thing's essence. That

means that it is 'the essential whatness' of a body of the character just assigned. Suppose that what is literally

an 'organ', like an axe, were a natural body, its 'essential whatness', would have been its essence, and so its

soul; if this disappeared from it, it would have ceased to be an axe, except in name. As it is, it is just an axe; it

wants the character which is required to make its whatness or formulable essence a soul; for that, it would

have had to be a natural body of a particular kind, viz. one having in itself the power of setting itself in

movement and arresting itself. Next, apply this doctrine in the case of the 'parts' of the living body. Suppose

that the eye were an animalsight would have been its soul, for sight is the substance or essence of the eye

which corresponds to the formula, the eye being merely the matter of seeing; when seeing is removed the eye

is no longer an eye, except in nameit is no more a real eye than the eye of a statue or of a painted figure. We

must now extend our consideration from the 'parts' to the whole living body; for what the departmental sense

is to the bodily part which is its organ, that the whole faculty of sense is to the whole sensitive body as such.

We must not understand by that which is 'potentially capable of living' what has lost the soul it had, but only

what still retains it; but seeds and fruits are bodies which possess the qualification. Consequently, while

waking is actuality in a sense corresponding to the cutting and the seeing, the soul is actuality in the sense

corresponding to the power of sight and the power in the tool; the body corresponds to what exists in

potentiality; as the pupil plus the power of sight constitutes the eye, so the soul plus the body constitutes the

From this it indubitably follows that the soul is inseparable from its body, or at any rate that certain parts of it

are (if it has parts) for the actuality of some of them is nothing but the actualities of their bodily parts. Yet

some may be separable because they are not the actualities of any body at all. Further, we have no light on the

problem whether the soul may not be the actuality of its body in the sense in which the sailor is the actuality

Since what is clear or logically more evident emerges from what in itself is confused but more observable by

us, we must reconsider our results from this point of view. For it is not enough for a definitive formula to

express as most now do the mere fact; it must include and exhibit the ground also. At present definitions are

given in a form analogous to the conclusion of a syllogism; e.g. What is squaring? The construction of an

equilateral rectangle equal to a given oblong rectangle. Such a definition is in form equivalent to a

conclusion. One that tells us that squaring is the discovery of a line which is a mean proportional between the

two unequal sides of the given rectangle discloses the ground of what is defined.

We resume our inquiry from a fresh startingpoint by calling attention to the fact that what has soul in it

differs from what has not, in that the former displays life. Now this word has more than one sense, and

provided any one alone of these is found in a thing we say that thing is living. Living, that is, may mean

thinking or perception or local movement and rest, or movement in the sense of nutrition, decay and growth.

Hence we think of plants also as living, for they are observed to possess in themselves an originative power

through which they increase or decrease in all spatial directions; they grow up and down, and everything that

grows increases its bulk alike in both directions or indeed in all, and continues to live so long as it can absorb

This power of selfnutrition can be isolated from the other powers mentioned, but not they from itin mortal

beings at least. The fact is obvious in plants; for it is the only psychic power they possess.

This is the originative power the possession of which leads us to speak of things as living at all, but it is the

possession of sensation that leads us for the first time to speak of living things as animals; for even those

beings which possess no power of local movement but do possess the power of sensation we call animals and

The primary form of sense is touch, which belongs to all animals. just as the power of selfnutrition can be

isolated from touch and sensation generally, so touch can be isolated from all other forms of sense. (By the

power of selfnutrition we mean that departmental power of the soul which is common to plants and animals:

all animals whatsoever are observed to have the sense of touch.) What the explanation of these two facts is,

we must discuss later. At present we must confine ourselves to saying that soul is the source of these

phenomena and is characterized by them, viz. by the powers of selfnutrition, sensation, thinking, and

Is each of these a soul or a part of a soul? And if a part, a part in what sense? A part merely distinguishable

by definition or a part distinct in local situation as well? In the case of certain of these powers, the answers to

these questions are easy, in the case of others we are puzzled what to say. just as in the case of plants which

when divided are observed to continue to live though removed to a distance from one another (thus showing

that in their case the soul of each individual plant before division was actually one, potentially many), so we

notice a similar result in other varieties of soul, i.e. in insects which have been cut in two; each of the

segments possesses both sensation and local movement; and if sensation, necessarily also imagination and

appetition; for, where there is sensation, there is also pleasure and pain, and, where these, necessarily also

We have no evidence as yet about mind or the power to think; it seems to be a widely different kind of soul,

differing as what is eternal from what is perishable; it alone is capable of existence in isolation from all other

psychic powers. All the other parts of soul, it is evident from what we have said, are, in spite of certain

statements to the contrary, incapable of separate existence though, of course, distinguishable by definition. If

opining is distinct from perceiving, to be capable of opining and to be capable of perceiving must be distinct,

and so with all the other forms of living above enumerated. Further, some animals possess all these parts of

soul, some certain of them only, others one only (this is what enables us to classify animals); the cause must

be considered later.' A similar arrangement is found also within the field of the senses; some classes of

animals have all the senses, some only certain of them, others only one, the most indispensable, touch.

Since the expression 'that whereby we live and perceive' has two meanings, just like the expression 'that

whereby we know'that may mean either (a) knowledge or (b) the soul, for we can speak of knowing by or

with either, and similarly that whereby we are in health may be either (a) health or (b) the body or some part

of the body; and since of the two terms thus contrasted knowledge or health is the name of a form, essence, or

ratio, or if we so express it an actuality of a recipient matterknowledge of what is capable of knowing,

health of what is capable of being made healthy (for the operation of that which is capable of originating

change terminates and has its seat in what is changed or altered); further, since it is the soul by or with which

primarily we live, perceive, and think:it follows that the soul must be a ratio or formulable essence, not a

matter or subject. For, as we said, word substance has three meanings form, matter, and the complex of both

and of these three what is called matter is potentiality, what is called form actuality. Since then the complex

here is the living thing, the body cannot be the actuality of the soul; it is the soul which is the actuality of a

certain kind of body. Hence the rightness of the view that the soul cannot be without a body, while it csnnot

he a body; it is not a body but something relative to a body. That is why it is in a body, and a body of a

definite kind. It was a mistake, therefore, to do as former thinkers did, merely to fit it into a body without

adding a definite specification of the kind or character of that body. Reflection confirms the observed fact;

the actuality of any given thing can only be realized in what is already potentially that thing, i.e. in a matter of

its own appropriate to it. From all this it follows that soul is an actuality or formulable essence of something

Of the psychic powers above enumerated some kinds of living things, as we have said, possess all, some less

than all, others one only. Those we have mentioned are the nutritive, the appetitive, the sensory, the

locomotive, and the power of thinking. Plants have none but the first, the nutritive, while another order of

living things has this plus the sensory. If any order of living things has the sensory, it must also have the

appetitive; for appetite is the genus of which desire, passion, and wish are the species; now all animals have

one sense at least, viz. touch, and whatever has a sense has the capacity for pleasure and pain and therefore

has pleasant and painful objects present to it, and wherever these are present, there is desire, for desire is just

appetition of what is pleasant. Further, all animals have the sense for food (for touch is the sense for food);

the food of all living things consists of what is dry, moist, hot, cold, and these are the qualities apprehended

by touch; all other sensible qualities are apprehended by touch only indirectly. Sounds, colours, and odours

contribute nothing to nutriment; flavours fall within the field of tangible qualities. Hunger and thirst are

forms of desire, hunger a desire for what is dry and hot, thirst a desire for what is cold and moist; flavour is a

sort of seasoning added to both. We must later clear up these points, but at present it may be enough to say

that all animals that possess the sense of touch have also appetition. The case of imagination is obscure; we

must examine it later. Certain kinds of animals possess in addition the power of locomotion, and still another

order of animate beings, i.e. man and possibly another order like man or superior to him, the power of

thinking, i.e. mind. It is now evident that a single definition can be given of soul only in the same sense as

one can be given of figure. For, as in that case there is no figure distinguishable and apart from triangle, so

here there is no soul apart from the forms of soul just enumerated. It is true that a highly general definition

can be given for figure which will fit all figures without expressing the peculiar nature of any figure. So here

in the case of soul and its specific forms. Hence it is absurd in this and similar cases to demand an absolutely

general definition which will fail to express the peculiar nature of anything that is, or again, omitting this, to

look for separate definitions corresponding to each infima species. The cases of figure and soul are exactly

parallel; for the particulars subsumed under the common name in both casesfigures and living

beingsconstitute a series, each successive term of which potentially contains its predecessor, e.g. the square

the triangle, the sensory power the selfnutritive. Hence we must ask in the case of each order of living

things, What is its soul, i.e. What is the soul of plant, animal, man? Why the terms are related in this serial

way must form the subject of later examination. But the facts are that the power of perception is never found

apart from the power of selfnutrition, whilein plantsthe latter is found isolated from the former. Again, no

sense is found apart from that of touch, while touch is found by itself; many animals have neither sight,

hearing, nor smell. Again, among living things that possess sense some have the power of locomotion, some

not. Lastly, certain living beingsa small minoritypossess calculation and thought, for (among mortal

beings) those which possess calculation have all the other powers above mentioned, while the converse does

not holdindeed some live by imagination alone, while others have not even imagination. The mind that

It is evident that the way to give the most adequate definition of soul is to seek in the case of each of its forms

It is necessary for the student of these forms of soul first to find a definition of each, expressive of what it is,

and then to investigate its derivative properties, But if we are to express what each is, viz. what the thinking

power is, or the perceptive, or the nutritive, we must go farther back and first give an account of thinking or

perceiving, for in the order of investigation the question of what an agent does precedes the question, what

enables it to do what it does. If this is correct, we must on the same ground go yet another step farther back

and have some clear view of the objects of each; thus we must start with these objects, e.g. with food, with

It follows that first of all we must treat of nutrition and reproduction, for the nutritive soul is found along with

all the others and is the most primitive and widely distributed power of soul, being indeed that one in virtue

of which all are said to have life. The acts in which it manifests itself are reproduction and the use of

foodreproduction, I say, because for any living thing that has reached its normal development and which is

unmutilated, and whose mode of generation is not spontaneous, the most natural act is the production of

another like itself, an animal producing an animal, a plant a plant, in order that, as far as its nature allows, it

may partake in the eternal and divine. That is the goal towards which all things strive, that for the sake of

which they do whatsoever their nature renders possible. The phrase 'for the sake of which' is ambiguous; it

may mean either (a) the end to achieve which, or (b) the being in whose interest, the act is done. Since then

no living thing is able to partake in what is eternal and divine by uninterrupted continuance (for nothing

perishable can for ever remain one and the same), it tries to achieve that end in the only way possible to it,

and success is possible in varying degrees; so it remains not indeed as the selfsame individual but continues

The soul is the cause or source of the living body. The terms cause and source have many senses. But the soul

is the cause of its body alike in all three senses which we explicitly recognize. It is (a) the source or origin of

That it is the last, is clear; for in everything the essence is identical with the ground of its being, and here, in

the case of living things, their being is to live, and of their being and their living the soul in them is the cause

or source. Further, the actuality of whatever is potential is identical with its formulable essence.

It is manifest that the soul is also the final cause of its body. For Nature, like mind, always does whatever it

does for the sake of something, which something is its end. To that something corresponds in the case of

animals the soul and in this it follows the order of nature; all natural bodies are organs of the soul. This is true

of those that enter into the constitution of plants as well as of those which enter into that of animals. This

shows that that the sake of which they are is soul. We must here recall the two senses of 'that for the sake of

which', viz. (a) the end to achieve which, and (b) the being in whose interest, anything is or is done.

We must maintain, further, that the soul is also the cause of the living body as the original source of local

movement. The power of locomotion is not found, however, in all living things. But change of quality and

change of quantity are also due to the soul. Sensation is held to be a qualitative alteration, and nothing except

what has soul in it is capable of sensation. The same holds of the quantitative changes which constitute

growth and decay; nothing grows or decays naturally except what feeds itself, and nothing feeds itself except

Empedocles is wrong in adding that growth in plants is to be explained, the downward rooting by the natural

tendency of earth to travel downwards, and the upward branching by the similar natural tendency of fire to

travel upwards. For he misinterprets up and down; up and down are not for all things what they are for the

whole Cosmos: if we are to distinguish and identify organs according to their functions, the roots of plants

are analogous to the head in animals. Further, we must ask what is the force that holds together the earth and

the fire which tend to travel in contrary directions; if there is no counteracting force, they will be torn

asunder; if there is, this must be the soul and the cause of nutrition and growth. By some the element of fire is

held to be the cause of nutrition and growth, for it alone of the primary bodies or elements is observed to feed

and increase itself. Hence the suggestion that in both plants and animals it is it which is the operative force. A

concurrent cause in a sense it certainly is, but not the principal cause, that is rather the soul; for while the

growth of fire goes on without limit so long as there is a supply of fuel, in the case of all complex wholes

formed in the course of nature there is a limit or ratio which determines their size and increase, and limit and

ratio are marks of soul but not of fire, and belong to the side of formulable essence rather than that of matter.

Nutrition and reproduction are due to one and the same psychic power. It is necessary first to give precision

to our account of food, for it is by this function of absorbing food that this psychic power is distinguished

from all the others. The current view is that what serves as food to a living thing is what is contrary to itnot

that in every pair of contraries each is food to the other: to be food a contrary must not only be transformable

into the other and vice versa, it must also in so doing increase the bulk of the other. Many a contrary is

transformed into its other and vice versa, where neither is even a quantum and so cannot increase in bulk, e.g.

an invalid into a healthy subject. It is clear that not even those contraries which satisfy both the conditions

mentioned above are food to one another in precisely the same sense; water may be said to feed fire, but not

fire water. Where the members of the pair are elementary bodies only one of the contraries, it would appear,

can be said to feed the other. But there is a difficulty here. One set of thinkers assert that like fed, as well as

increased in amount, by like. Another set, as we have said, maintain the very reverse, viz. that what feeds and

what is fed are contrary to one another; like, they argue, is incapable of being affected by like; but food is

changed in the process of digestion, and change is always to what is opposite or to what is intermediate.

Further, food is acted upon by what is nourished by it, not the other way round, as timber is worked by a

carpenter and not conversely; there is a change in the carpenter but it is merely a change from notworking to

working. In answering this problem it makes all the difference whether we mean by 'the food' the 'finished' or

the 'raw' product. If we use the word food of both, viz. of the completely undigested and the completely

digested matter, we can justify both the rival accounts of it; taking food in the sense of undigested matter, it is

the contrary of what is fed by it, taking it as digested it is like what is fed by it. Consequently it is clear that in

Since nothing except what is alive can be fed, what is fed is the besouled body and just because it has soul in

it. Hence food is essentially related to what has soul in it. Food has a power which is other than the power to

increase the bulk of what is fed by it; so far forth as what has soul in it is a quantum, food may increase its

quantity, but it is only so far as what has soul in it is a 'thissomewhat' or substance that food acts as food; in

that case it maintains the being of what is fed, and that continues to be what it is so long as the process of

nutrition continues. Further, it is the agent in generation, i.e. not the generation of the individual fed but the

reproduction of another like it; the substance of the individual fed is already in existence; the existence of no

Hence the psychic power which we are now studying may be described as that which tends to maintain

whatever has this power in it of continuing such as it was, and food helps it to do its work. That is why, if

The process of nutrition involves three factors, (a) what is fed, (b) that wherewith it is fed, (c) what does the

feeding; of these (c) is the first soul, (a) the body which has that soul in it, (b) the food. But since it is right to

call things after the ends they realize, and the end of this soul is to generate another being like that in which it

is, the first soul ought to be named the reproductive soul. The expression (b) 'wherewith it is fed' is

ambiguous just as is the expression 'wherewith the ship is steered'; that may mean either (i) the hand or (ii)

the rudder, i.e. either (i) what is moved and sets in movement, or (ii) what is merely moved. We can apply

this analogy here if we recall that all food must be capable of being digested, and that what produces

digestion is warmth; that is why everything that has soul in it possesses warmth.

We have now given an outline account of the nature of food; further details must be given in the appropriate

Having made these distinctions let us now speak of sensation in the widest sense. Sensation depends, as we

have said, on a process of movement or affection from without, for it is held to be some sort of change of

quality. Now some thinkers assert that like is affected only by like; in what sense this is possible and in what

sense impossible, we have explained in our general discussion of acting and being acted upon.

Here arises a problem: why do we not perceive the senses themselves as well as the external objects of sense,

or why without the stimulation of external objects do they not produce sensation, seeing that they contain in

themselves fire, earth, and all the other elements, which are the direct or indirect objects is so of sense? It is

clear that what is sensitive is only potentially, not actually. The power of sense is parallel to what is

combustible, for that never ignites itself spontaneously, but requires an agent which has the power of starting

ignition; otherwise it could have set itself on fire, and would not have needed actual fire to set it ablaze.

In reply we must recall that we use the word 'perceive' in two ways, for we say (a) that what has the power to

hear or see, 'sees' or 'hears', even though it is at the moment asleep, and also (b) that what is actually seeing or

hearing, 'sees' or 'hears'. Hence 'sense' too must have two meanings, sense potential, and sense actual.

Similarly 'to be a sentient' means either (a) to have a certain power or (b) to manifest a certain activity. To

begin with, for a time, let us speak as if there were no difference between (i) being moved or affected, and (ii)

being active, for movement is a kind of activityan imperfect kind, as has elsewhere been explained.

Everything that is acted upon or moved is acted upon by an agent which is actually at work. Hence it is that in

one sense, as has already been stated, what acts and what is acted upon are like, in another unlike, i.e. prior to

But we must now distinguish not only between what is potential and what is actual but also different senses

in which things can be said to be potential or actual; up to now we have been speaking as if each of these

phrases had only one sense. We can speak of something as 'a knower' either (a) as when we say that man is a

knower, meaning that man falls within the class of beings that know or have knowledge, or (b) as when we

are speaking of a man who possesses a knowledge of grammar; each of these is so called as having in him a

certain potentiality, but there is a difference between their respective potentialities, the one (a) being a

potential knower, because his kind or matter is such and such, the other (b), because he can in the absence of

any external counteracting cause realize his knowledge in actual knowing at will. This implies a third

meaning of 'a knower' (c), one who is already realizing his knowledgehe is a knower in actuality and in the

most proper sense is knowing, e.g. this A. Both the former are potential knowers, who realize their respective

potentialities, the one (a) by change of quality, i.e. repeated transitions from one state to its opposite under

instruction, the other (b) by the transition from the inactive possession of sense or grammar to their active

Also the expression 'to be acted upon' has more than one meaning; it may mean either (a) the extinction of

one of two contraries by the other, or (b) the maintenance of what is potential by the agency of what is actual

and already like what is acted upon, with such likeness as is compatible with one's being actual and the other

potential. For what possesses knowledge becomes an actual knower by a transition which is either not an

alteration of it at all (being in reality a development into its true self or actuality) or at least an alteration in a

Hence it is wrong to speak of a wise man as being 'altered' when he uses his wisdom, just as it would be

absurd to speak of a builder as being altered when he is using his skill in building a house.

What in the case of knowing or understanding leads from potentiality to actuality ought not to be called

teaching but something else. That which starting with the power to know learns or acquires knowledge

through the agency of one who actually knows and has the power of teaching either (a) ought not to be said

'to be acted upon' at all or (b) we must recognize two senses of alteration, viz. (i) the substitution of one

quality for another, the first being the contrary of the second, or (ii) the development of an existent quality

In the case of what is to possess sense, the first transition is due to the action of the male parent and takes

place before birth so that at birth the living thing is, in respect of sensation, at the stage which corresponds to

the possession of knowledge. Actual sensation corresponds to the stage of the exercise of knowledge. But

between the two cases compared there is a difference; the objects that excite the sensory powers to activity,

the seen, the heard, are outside. The ground of this difference is that what actual sensation apprehends is

individuals, while what knowledge apprehends is universals, and these are in a sense within the soul. That is

why a man can exercise his knowledge when he wishes, but his sensation does not depend upon himself a

sensible object must be there. A similar statement must be made about our knowledge of what is sensibleon

A later more appropriate occasion may be found thoroughly to clear up all this. At present it must be enough

to recognize the distinctions already drawn; a thing may be said to be potential in either of two senses, (a) in

the sense in which we might say of a boy that he may become a general or (b) in the sense in which we might

say the same of an adult, and there are two corresponding senses of the term 'a potential sentient'. There are

no separate names for the two stages of potentiality; we have pointed out that they are different and how they

are different. We cannot help using the incorrect terms 'being acted upon or altered' of the two transitions

involved. As we have said, has the power of sensation is potentially like what the perceived object is actually;

that is, while at the beginning of the process of its being acted upon the two interacting factors are dissimilar,

at the end the one acted upon is assimilated to the other and is identical in quality with it.

In dealing with each of the senses we shall have first to speak of the objects which are perceptible by each.

The term 'object of sense' covers three kinds of objects, two kinds of which are, in our language, directly

perceptible, while the remaining one is only incidentally perceptible. Of the first two kinds one (a) consists of

what is perceptible by a single sense, the other (b) of what is perceptible by any and all of the senses. I call by

the name of special object of this or that sense that which cannot be perceived by any other sense than that

one and in respect of which no error is possible; in this sense colour is the special object of sight, sound of

hearing, flavour of taste. Touch, indeed, discriminates more than one set of different qualities. Each sense has

one kind of object which it discerns, and never errs in reporting that what is before it is colour or sound

(though it may err as to what it is that is coloured or where that is, or what it is that is sounding or where that

is.) Such objects are what we propose to call the special objects of this or that sense.

'Common sensibles' are movement, rest, number, figure, magnitude; these are not peculiar to any one sense,

but are common to all. There are at any rate certain kinds of movement which are perceptible both by touch

We speak of an incidental object of sense where e.g. the white object which we see is the son of Diares; here

because 'being the son of Diares' is incidental to the directly visible white patch we speak of the son of Diares

as being (incidentally) perceived or seen by us. Because this is only incidentally an object of sense, it in no

way as such affects the senses. Of the two former kinds, both of which are in their own nature perceptible by

sense, the first kindthat of special objects of the several sensesconstitute the objects of sense in the strictest

sense of the term and it is to them that in the nature of things the structure of each several sense is adapted.

The object of sight is the visible, and what is visible is (a) colour and (b) a certain kind of object which can be

described in words but which has no single name; what we mean by (b) will be abundantly clear as we

proceed. Whatever is visible is colour and colour is what lies upon what is in its own nature visible; 'in its

own nature' here means not that visibility is involved in the definition of what thus underlies colour, but that

that substratum contains in itself the cause of visibility. Every colour has in it the power to set in movement

what is actually transparent; that power constitutes its very nature. That is why it is not visible except with the

help of light; it is only in light that the colour of a thing is seen. Hence our first task is to explain what light

Now there clearly is something which is transparent, and by 'transparent' I mean what is visible, and yet not

visible in itself, but rather owing its visibility to the colour of something else; of this character are air, water,

and many solid bodies. Neither air nor water is transparent because it is air or water; they are transparent

because each of them has contained in it a certain substance which is the same in both and is also found in the

eternal body which constitutes the uppermost shell of the physical Cosmos. Of this substance light is the

activitythe activity of what is transparent so far forth as it has in it the determinate power of becoming

transparent; where this power is present, there is also the potentiality of the contrary, viz. darkness. Light is as

it were the proper colour of what is transparent, and exists whenever the potentially transparent is excited to

actuality by the influence of fire or something resembling 'the uppermost body'; for fire too contains

We have now explained what the transparent is and what light is; light is neither fire nor any kind whatsoever

of body nor an efflux from any kind of body (if it were, it would again itself be a kind of body)it is the

presence of fire or something resembling fire in what is transparent. It is certainly not a body, for two bodies

cannot be present in the same place. The opposite of light is darkness; darkness is the absence from what is

transparent of the corresponding positive state above characterized; clearly therefore, light is just the presence

Empedocles (and with him all others who used the same forms of expression) was wrong in speaking of light

as 'travelling' or being at a given moment between the earth and its envelope, its movement being

unobservable by us; that view is contrary both to the clear evidence of argument and to the observed facts; if

the distance traversed were short, the movement might have been unobservable, but where the distance is

from extreme East to extreme West, the draught upon our powers of belief is too great.

What is capable of taking on colour is what in itself is colourless, as what can take on sound is what is

soundless; what is colourless includes (a) what is transparent and (b) what is invisible or scarcely visible, i.e.

what is 'dark'. The latter (b) is the same as what is transparent, when it is potentially, not of course when it is

actually transparent; it is the same substance which is now darkness, now light.

Not everything that is visible depends upon light for its visibility. This is only true of the 'proper' colour of

things. Some objects of sight which in light are invisible, in darkness stimulate the sense; that is, things that

appear fiery or shining. This class of objects has no simple common name, but instances of it are fungi, flesh,

heads, scales, and eyes of fish. In none of these is what is seen their own proper' colour. Why we see these at

all is another question. At present what is obvious is that what is seen in light is always colour. That is why

without the help of light colour remains invisible. Its being colour at all means precisely its having in it the

power to set in movement what is already actually transparent, and, as we have seen, the actuality of what is

The following experiment makes the necessity of a medium clear. If what has colour is placed in immediate

contact with the eye, it cannot be seen. Colour sets in movement not the sense organ but what is transparent,

e.g. the air, and that, extending continuously from the object to the organ, sets the latter in movement.

Democritus misrepresents the facts when he expresses the opinion that if the interspace were empty one could

distinctly see an ant on the vault of the sky; that is an impossibility. Seeing is due to an affection or change of

what has the perceptive faculty, and it cannot be affected by the seen colour itself; it remains that it must be

affected by what comes between. Hence it is indispensable that there be something in betweenif there were

nothing, so far from seeing with greater distinctness, we should see nothing at all.

We have now explained the cause why colour cannot be seen otherwise than in light. Fire on the other hand is

seen both in darkness and in light; this double possibility follows necessarily from our theory, for it is just fire

The same account holds also of sound and smell; if the object of either of these senses is in immediate contact

with the organ no sensation is produced. In both cases the object sets in movement only what lies between,

and this in turn sets the organ in movement: if what sounds or smells is brought into immediate contact with

the organ, no sensation will be produced. The same, in spite of all appearances, applies also to touch and

taste; why there is this apparent difference will be clear later. What comes between in the case of sounds is

air; the corresponding medium in the case of smell has no name. But, corresponding to what is transparent in

the case of colour, there is a quality found both in air and water, which serves as a medium for what has

smellI say 'in water' because animals that live in water as well as those that live on land seem to possess the

sense of smell, and 'in air' because man and all other land animals that breathe, perceive smells only when

Sound may mean either of two things (a) actual, and (b) potential, sound. There are certain things which, as

we say, 'have no sound', e.g. sponges or wool, others which have, e.g. bronze and in general all things which

are smooth and solidthe latter are said to have a sound because they can make a sound, i.e. can generate

Actual sound requires for its occurrence (i, ii) two such bodies and (iii) a space between them; for it is

generated by an impact. Hence it is impossible for one body only to generate a soundthere must be a body

impinging and a body impinged upon; what sounds does so by striking against something else, and this is

As we have said, not all bodies can by impact on one another produce sound; impact on wool makes no

sound, while the impact on bronze or any body which is smooth and hollow does. Bronze gives out a sound

when struck because it is smooth; bodies which are hollow owing to reflection repeat the original impact over

and over again, the body originally set in movement being unable to escape from the concavity.

Further, we must remark that sound is heard both in air and in water, though less distinctly in the latter. Yet

neither air nor water is the principal cause of sound. What is required for the production of sound is an impact

of two solids against one another and against the air. The latter condition is satisfied when the air impinged

That is why it must be struck with a sudden sharp blow, if it is to soundthe movement of the whip must

outrun the dispersion of the air, just as one might get in a stroke at a heap or whirl of sand as it was traveling

An echo occurs, when, a mass of air having been unified, bounded, and prevented from dissipation by the

containing walls of a vessel, the air originally struck by the impinging body and set in movement by it

rebounds from this mass of air like a ball from a wall. It is probable that in all generation of sound echo takes

place, though it is frequently only indistinctly heard. What happens here must be analogous to what happens

in the case of light; light is always reflectedotherwise it would not be diffused and outside what was directly

illuminated by the sun there would be blank darkness; but this reflected light is not always strong enough, as

it is when it is reflected from water, bronze, and other smooth bodies, to cast a shadow, which is the

It is rightly said that an empty space plays the chief part in the production of hearing, for what people mean

by 'the vacuum' is the air, which is what causes hearing, when that air is set in movement as one continuous

mass; but owing to its friability it emits no sound, being dissipated by impinging upon any surface which is

not smooth. When the surface on which it impinges is quite smooth, what is produced by the original impact

is a united mass, a result due to the smoothness of the surface with which the air is in contact at the other end.

What has the power of producing sound is what has the power of setting in movement a single mass of air

which is continuous from the impinging body up to the organ of hearing. The organ of hearing is physically

united with air, and because it is in air, the air inside is moved concurrently with the air outside. Hence

animals do not hear with all parts of their bodies, nor do all parts admit of the entrance of air; for even the

part which can be moved and can sound has not air everywhere in it. Air in itself is, owing to its friability,

quite soundless; only when its dissipation is prevented is its movement sound. The air in the ear is built into a

chamber just to prevent this dissipating movement, in order that the animal may accurately apprehend all

varieties of the movements of the air outside. That is why we hear also in water, viz. because the water cannot

get into the air chamber or even, owing to the spirals, into the outer ear. If this does happen, hearing ceases,

as it also does if the tympanic membrane is damaged, just as sight ceases if the membrane covering the pupil

is damaged. It is also a test of deafness whether the ear does or does not reverberate like a horn; the air inside

the ear has always a movement of its own, but the sound we hear is always the sounding of something else,

not of the organ itself. That is why we say that we hear with what is empty and echoes, viz. because what we

Which is it that 'sounds', the striking body or the struck? Is not the answer 'it is both, but each in a different

way'? Sound is a movement of what can rebound from a smooth surface when struck against it. As we have

explained' not everything sounds when it strikes or is struck, e.g. if one needle is struck against another,

neither emits any sound. In order, therefore, that sound may be generated, what is struck must be smooth, to

The distinctions between different sounding bodies show themselves only in actual sound; as without the help

of light colours remain invisible, so without the help of actual sound the distinctions between acute and grave

sounds remain inaudible. Acute and grave are here metaphors, transferred from their proper sphere, viz. that

of touch, where they mean respectively (a) what moves the sense much in a short time, (b) what moves the

sense little in a long time. Not that what is sharp really moves fast, and what is grave, slowly, but that the

difference in the qualities of the one and the other movement is due to their respective speeds. There seems to

be a sort of parallelism between what is acute or grave to hearing and what is sharp or blunt to touch; what is

sharp as it were stabs, while what is blunt pushes, the one producing its effect in a short, the other in a long

Let the foregoing suffice as an analysis of sound. Voice is a kind of sound characteristic of what has soul in

it; nothing that is without soul utters voice, it being only by a metaphor that we speak of the voice of the flute

or the lyre or generally of what (being without soul) possesses the power of producing a succession of notes

which differ in length and pitch and timbre. The metaphor is based on the fact that all these differences are

found also in voice. Many animals are voiceless, e.g. all nonsanuineous animals and among sanguineous

animals fish. This is just what we should expect, since voice is a certain movement of air. The fish, like those

in the Achelous, which are said to have voice, really make the sounds with their gills or some similar organ.

Voice is the sound made by an animal, and that with a special organ. As we saw, everything that makes a

sound does so by the impact of something (a) against something else, (b) across a space, (c) filled with air;

hence it is only to be expected that no animals utter voice except those which take in air. Once air is

inbreathed, Nature uses it for two different purposes, as the tongue is used both for tasting and for

articulating; in that case of the two functions tasting is necessary for the animal's existence (hence it is found

more widely distributed), while articulate speech is a luxury subserving its possessor's wellbeing; similarly

in the former case Nature employs the breath both as an indispensable means to the regulation of the inner

temperature of the living body and also as the matter of articulate voice, in the interests of its possessor's

The organ of respiration is the windpipe, and the organ to which this is related as means to end is the lungs.

The latter is the part of the body by which the temperature of land animals is raised above that of all others.

But what primarily requires the air drawn in by respiration is not only this but the region surrounding the

Voice then is the impact of the inbreathed air against the 'windpipe', and the agent that produces the impact is

the soul resident in these parts of the body. Not every sound, as we said, made by an animal is voice (even

with the tongue we may merely make a sound which is not voice, or without the tongue as in coughing); what

produces the impact must have soul in it and must be accompanied by an act of imagination, for voice is a

sound with a meaning, and is not merely the result of any impact of the breath as in coughing; in voice the

breath in the windpipe is used as an instrument to knock with against the walls of the windpipe. This is

confirmed by our inability to speak when we are breathing either out or inwe can only do so by holding our

breath; we make the movements with the breath so checked. It is clear also why fish are voiceless; they have

no windpipe. And they have no windpipe because they do not breathe or take in air. Why they do not is a

Smell and its object are much less easy to determine than what we have hitherto discussed; the distinguishing

characteristic of the object of smell is less obvious than those of sound or colour. The ground of this is that

our power of smell is less discriminating and in general inferior to that of many species of animals; men have

a poor sense of smell and our apprehension of its proper objects is inseparably bound up with and so confused

by pleasure and pain, which shows that in us the organ is inaccurate. It is probable that there is a parallel

failure in the perception of colour by animals that have hard eyes: probably they discriminate differences of

colour only by the presence or absence of what excites fear, and that it is thus that human beings distinguish

smells. It seems that there is an analogy between smell and taste, and that the species of tastes run parallel to

those of smellsthe only difference being that our sense of taste is more discriminating than our sense of

smell, because the former is a modification of touch, which reaches in man the maximum of discriminative

accuracy. While in respect of all the other senses we fall below many species of animals, in respect of touch

we far excel all other species in exactness of discrimination. That is why man is the most intelligent of all

animals. This is confirmed by the fact that it is to differences in the organ of touch and to nothing else that the

differences between man and man in respect of natural endowment are due; men whose flesh is hard are

As flavours may be divided into (a) sweet, (b) bitter, so with smells. In some things the flavour and the smell

have the same quality, i.e. both are sweet or both bitter, in others they diverge. Similarly a smell, like a

flavour, may be pungent, astringent, acid, or succulent. But, as we said, because smells are much less easy to

discriminate than flavours, the names of these varieties are applied to smells only metaphorically; for

example 'sweet' is extended from the taste to the smell of saffron or honey, 'pungent' to that of thyme, and so

In the same sense in which hearing has for its object both the audible and the inaudible, sight both the visible

and the invisible, smell has for its object both the odorous and the inodorous. 'Inodorous' may be either (a)

what has no smell at all, or (b) what has a small or feeble smell. The same ambiguity lurks in the word

Smelling, like the operation of the senses previously examined, takes place through a medium, i.e. through air

or waterI add water, because wateranimals too (both sanguineous and nonsanguineous) seem to smell just

as much as landanimals; at any rate some of them make directly for their food from a distance if it has any

scent. That is why the following facts constitute a problem for us. All animals smell in the same way, but

man smells only when he inhales; if he exhales or holds his breath, he ceases to smell, no difference being

made whether the odorous object is distant or near, or even placed inside the nose and actually on the wall of

the nostril; it is a disability common to all the senses not to perceive what is in immediate contact with the

organ of sense, but our failure to apprehend what is odorous without the help of inhalation is peculiar (the

fact is obvious on making the experiment). Now since bloodless animals do not breathe, they must, it might

be argued, have some novel sense not reckoned among the usual five. Our reply must be that this is

impossible, since it is scent that is perceived; a sense that apprehends what is odorous and what has a good or

bad odour cannot be anything but smell. Further, they are observed to be deleteriously effected by the same

strong odours as man is, e.g. bitumen, sulphur, and the like. These animals must be able to smell without

being able to breathe. The probable explanation is that in man the organ of smell has a certain superiority

over that in all other animals just as his eyes have over those of hardeyed animals. Man's eyes have in the

eyelids a kind of shelter or envelope, which must be shifted or drawn back in order that we may see, while

hardeyed animals have nothing of the kind, but at once see whatever presents itself in the transparent

medium. Similarly in certain species of animals the organ of smell is like the eye of hardeyed animals,

uncurtained, while in others which take in air it probably has a curtain over it, which is drawn back in

inhalation, owing to the dilating of the veins or pores. That explains also why such animals cannot smell

under water; to smell they must first inhale, and that they cannot do under water.

Smells come from what is dry as flavours from what is moist. Consequently the organ of smell is potentially

What can be tasted is always something that can be touched, and just for that reason it cannot be perceived

through an interposed foreign body, for touch means the absence of any intervening body. Further, the

flavoured and tasteable body is suspended in a liquid matter, and this is tangible. Hence, if we lived in water,

we should perceive a sweet object introduced into the water, but the water would not be the medium through

which we perceived; our perception would be due to the solution of the sweet substance in what we imbibed,

just as if it were mixed with some drink. There is no parallel here to the perception of colour, which is due

neither to any blending of anything with anything, nor to any efflux of anything from anything. In the case of

taste, there is nothing corresponding to the medium in the case of the senses previously discussed; but as the

object of sight is colour, so the object of taste is flavour. But nothing excites a perception of flavour without

the help of liquid; what acts upon the sense of taste must be either actually or potentially liquid like what is

saline; it must be both (a) itself easily dissolved, and (b) capable of dissolving along with itself the tongue.

Taste apprehends both (a) what has taste and (b) what has no taste, if we mean by (b) what has only a slight

or feeble flavour or what tends to destroy the sense of taste. In this it is exactly parallel to sight, which

apprehends both what is visible and what is invisible (for darkness is invisible and yet is discriminated by

sight; so is, in a different way, what is over brilliant), and to hearing, which apprehends both sound and

silence, of which the one is audible and the other inaudible, and also overloud sound. This corresponds in

the case of hearing to overbright light in the case of sight. As a faint sound is 'inaudible', so in a sense is a

loud or violent sound. The word 'invisible' and similar privative terms cover not only (a) what is simply

without some power, but also (b) what is adapted by nature to have it but has not it or has it only in a very

low degree, as when we say that a species of swallow is 'footless' or that a variety of fruit is 'stoneless'. So too

taste has as its object both what can be tasted and the tastelessthe latter in the sense of what has little flavour

or a bad flavour or one destructive of taste. The difference between what is tasteless and what is not seems to

rest ultimately on that between what is drinkable and what is undrinkable both are tasteable, but the latter is

bad and tends to destroy taste, while the former is the normal stimulus of taste. What is drinkable is the

Since what can be tasted is liquid, the organ for its perception cannot be either (a) actually liquid or (b)

incapable of becoming liquid. Tasting means a being affected by what can be tasted as such; hence the organ

of taste must be liquefied, and so to start with must be nonliquid but capable of liquefaction without loss of

its distinctive nature. This is confirmed by the fact that the tongue cannot taste either when it is too dry or

when it is too moist; in the latter case what occurs is due to a contact with the preexistent moisture in the

tongue itself, when after a foretaste of some strong flavour we try to taste another flavour; it is in this way

that sick persons find everything they taste bitter, viz. because, when they taste, their tongues are overflowing

The species of flavour are, as in the case of colour, (a) simple, i.e. the two contraries, the sweet and the bitter,

(b) secondary, viz. (i) on the side of the sweet, the succulent, (ii) on the side of the bitter, the saline, (iii)

between these come the pungent, the harsh, the astringent, and the acid; these pretty well exhaust the varieties

of flavour. It follows that what has the power of tasting is what is potentially of that kind, and that what is

tasteable is what has the power of making it actually what it itself already is.

Whatever can be said of what is tangible, can be said of touch, and vice versa; if touch is not a single sense

but a group of senses, there must be several kinds of what is tangible. It is a problem whether touch is a single

sense or a group of senses. It is also a problem, what is the organ of touch; is it or is it not the flesh (including

what in certain animals is homologous with flesh)? On the second view, flesh is 'the medium' of touch, the

real organ being situated farther inward. The problem arises because the field of each sense is according to

the accepted view determined as the range between a single pair of contraries, white and black for sight, acute

and grave for hearing, bitter and sweet for taste; but in the field of what is tangible we find several such pairs,

hot cold, dry moist, hard soft, This problem finds a partial solution, when it is recalled that in the case of the

other senses more than one pair of contraries are to be met with, e.g. in sound not only acute and grave but

loud and soft, smooth and rough, there are similar contrasts in the field of colour. Nevertheless we are unable

clearly to detect in the case of touch what the single subject is which underlies the contrasted qualities and

To the question whether the organ of touch lies inward or not (i.e. whether we need look any farther than the

flesh), no indication in favour of the second answer can be drawn from the fact that if the object comes into

contact with the flesh it is at once perceived. For even under present conditions if the experiment is made of

making a web and stretching it tight over the flesh, as soon as this web is touched the sensation is reported in

the same manner as before, yet it is clear that the or is gan is not in this membrane. If the membrane could be

grown on to the flesh, the report would travel still quicker. The flesh plays in touch very much the same part

as would be played in the other senses by an airenvelope growing round our body; had we such an envelope

attached to us we should have supposed that it was by a single organ that we perceived sounds, colours, and

smells, and we should have taken sight, hearing, and smell to be a single sense. But as it is, because that

through which the different movements are transmitted is not naturally attached to our bodies, the difference

of the various senseorgans is too plain to miss. But in the case of touch the obscurity remains.

There must be such a naturally attached 'medium' as flesh, for no living body could be constructed of air or

water; it must be something solid. Consequently it must be composed of earth along with these, which is just

what flesh and its analogue in animals which have no true flesh tend to be. Hence of necessity the medium

through which are transmitted the manifoldly contrasted tactual qualities must be a body naturally attached to

the organism. That they are manifold is clear when we consider touching with the tongue; we apprehend at

the tongue all tangible qualities as well as flavour. Suppose all the rest of our flesh was, like the tongue,

sensitive to flavour, we should have identified the sense of taste and the sense of touch; what saves us from

this identification is the fact that touch and taste are not always found together in the same part of the body.

The following problem might be raised. Let us assume that every body has depth, i.e. has three dimensions,

and that if two bodies have a third body between them they cannot be in contact with one another; let us

remember that what is liquid is a body and must be or contain water, and that if two bodies touch one another

under water, their touching surfaces cannot be dry, but must have water between, viz. the water which wets

their bounding surfaces; from all this it follows that in water two bodies cannot be in contact with one

another. The same holds of two bodies in airair being to bodies in air precisely what water is to bodies in

waterbut the facts are not so evident to our observation, because we live in air, just as animals that live in

water would not notice that the things which touch one another in water have wet surfaces. The problem,

then, is: does the perception of all objects of sense take place in the same way, or does it not, e.g. taste and

touch requiring contact (as they are commonly thought to do), while all other senses perceive over a distance?

The distinction is unsound; we perceive what is hard or soft, as well as the objects of hearing, sight, and

smell, through a 'medium', only that the latter are perceived over a greater distance than the former; that is

why the facts escape our notice. For we do perceive everything through a medium; but in these cases the fact

escapes us. Yet, to repeat what we said before, if the medium for touch were a membrane separating us from

the object without our observing its existence, we should be relatively to it in the same condition as we are

now to air or water in which we are immersed; in their case we fancy we can touch objects, nothing coming

in between us and them. But there remains this difference between what can be touched and what can be seen

or can sound; in the latter two cases we perceive because the medium produces a certain effect upon us,

whereas in the perception of objects of touch we are affected not by but along with the medium; it is as if a

man were struck through his shield, where the shock is not first given to the shield and passed on to the man,

In general, flesh and the tongue are related to the real organs of touch and taste, as air and water are to those

of sight, hearing, and smell. Hence in neither the one case nor the other can there be any perception of an

object if it is placed immediately upon the organ, e.g. if a white object is placed on the surface of the eye.

This again shows that what has the power of perceiving the tangible is seated inside. Only so would there be a

complete analogy with all the other senses. In their case if you place the object on the organ it is not

perceived, here if you place it on the flesh it is perceived; therefore flesh is not the organ but the medium of

What can be touched are distinctive qualities of body as body; by such differences I mean those which

characterize the elements, viz, hot cold, dry moist, of which we have spoken earlier in our treatise on the

elements. The organ for the perception of these is that of touchthat part of the body in which primarily the

sense of touch resides. This is that part which is potentially such as its object is actually: for all

senseperception is a process of being so affected; so that that which makes something such as it itself

actually is makes the other such because the other is already potentially such. That is why when an object of

touch is equally hot and cold or hard and soft we cannot perceive; what we perceive must have a degree of

the sensible quality lying beyond the neutral point. This implies that the sense itself is a 'mean' between any

two opposite qualities which determine the field of that sense. It is to this that it owes its power of discerning

the objects in that field. What is 'in the middle' is fitted to discern; relatively to either extreme it can put itself

in the place of the other. As what is to perceive both white and black must, to begin with, be actually neither

but potentially either (and so with all the other senseorgans), so the organ of touch must be neither hot nor

Further, as in a sense sight had for its object both what was visible and what was invisible (and there was a

parallel truth about all the other senses discussed), so touch has for its object both what is tangible and what

is intangible. Here by 'intangible' is meant (a) what like air possesses some quality of tangible things in a very

slight degree and (b) what possesses it in an excessive degree, as destructive things do.

(A) By a 'sense' is meant what has the power of receiving into itself the sensible forms of things without the

matter. This must be conceived of as taking place in the way in which a piece of wax takes on the impress of

a signetring without the iron or gold; we say that what produces the impression is a signet of bronze or gold,

but its particular metallic constitution makes no difference: in a similar way the sense is affected by what is

coloured or flavoured or sounding, but it is indifferent what in each case the substance is; what alone matters

(B) By 'an organ of sense' is meant that in which ultimately such a power is seated.

The sense and its organ are the same in fact, but their essence is not the same. What perceives is, of course, a

spatial magnitude, but we must not admit that either the having the power to perceive or the sense itself is a

magnitude; what they are is a certain ratio or power in a magnitude. This enables us to explain why objects of

sense which possess one of two opposite sensible qualities in a degree largely in excess of the other opposite

destroy the organs of sense; if the movement set up by an object is too strong for the organ, the equipoise of

contrary qualities in the organ, which just is its sensory power, is disturbed; it is precisely as concord and

tone are destroyed by too violently twanging the strings of a lyre. This explains also why plants cannot

perceive. in spite of their having a portion of soul in them and obviously being affected by tangible objects

themselves; for undoubtedly their temperature can be lowered or raised. The explanation is that they have no

mean of contrary qualities, and so no principle in them capable of taking on the forms of sensible objects

without their matter; in the case of plants the affection is an affection by formandmatter together. The

problem might be raised: Can what cannot smell be said to be affected by smells or what cannot see by

colours, and so on? It might be said that a smell is just what can be smelt, and if it produces any effect it can

only be so as to make something smell it, and it might be argued that what cannot smell cannot be affected by

smells and further that what can smell can be affected by it only in so far as it has in it the power to smell

(similarly with the proper objects of all the other senses). Indeed that this is so is made quite evident as

follows. Light or darkness, sounds and smells leave bodies quite unaffected; what does affect bodies is not

these but the bodies which are their vehicles, e.g. what splits the trunk of a tree is not the sound of the thunder

but the air which accompanies thunder. Yes, but, it may be objected, bodies are affected by what is tangible

and by flavours. If not, by what are things that are without soul affected, i.e. altered in quality? Must we not,

then, admit that the objects of the other senses also may affect them? Is not the true account this, that all

bodies are capable of being affected by smells and sounds, but that some on being acted upon, having no

boundaries of their own, disintegrate, as in the instance of air, which does become odorous, showing that

some effect is produced on it by what is odorous? But smelling is more than such an affection by what is

odorouswhat more? Is not the answer that, while the air owing to the momentary duration of the action upon

it of what is odorous does itself become perceptible to the sense of smell, smelling is an observing of the

THAT there is no sixth sense in addition to the five enumeratedsight, hearing, smell, taste, touchmay be

If we have actually sensation of everything of which touch can give us sensation (for all the qualities of the

tangible qua tangible are perceived by us through touch); and if absence of a sense necessarily involves

absence of a senseorgan; and if (1) all objects that we perceive by immediate contact with them are

perceptible by touch, which sense we actually possess, and (2) all objects that we perceive through media, i.e.

without immediate contact, are perceptible by or through the simple elements, e.g. air and water (and this is

so arranged that (a) if more than one kind of sensible object is perceivable through a single medium, the

possessor of a senseorgan homogeneous with that medium has the power of perceiving both kinds of

objects; for example, if the senseorgan is made of air, and air is a medium both for sound and for colour;

and that (b) if more than one medium can transmit the same kind of sensible objects, as e.g. water as well as

air can transmit colour, both being transparent, then the possessor of either alone will be able to perceive the

kind of objects transmissible through both); and if of the simple elements two only, air and water, go to form

senseorgans (for the pupil is made of water, the organ of hearing is made of air, and the organ of smell of

one or other of these two, while fire is found either in none or in allwarmth being an essential condition of

all sensibilityand earth either in none or, if anywhere, specially mingled with the components of the organ

of touch; wherefore it would remain that there can be no senseorgan formed of anything except water and

air); and if these senseorgans are actually found in certain animals;then all the possible senses are

possessed by those animals that are not imperfect or mutilated (for even the mole is observed to have eyes

beneath its skin); so that, if there is no fifth element and no property other than those which belong to the four

Further, there cannot be a special senseorgan for the common sensibles either, i.e. the objects which we

perceive incidentally through this or that special sense, e.g. movement, rest, figure, magnitude, number,

unity; for all these we perceive by movement, e.g. magnitude by movement, and therefore also figure (for

figure is a species of magnitude), what is at rest by the absence of movement: number is perceived by the

negation of continuity, and by the special sensibles; for each sense perceives one class of sensible objects. So

that it is clearly impossible that there should be a special sense for any one of the common sensibles, e.g.

movement; for, if that were so, our perception of it would be exactly parallel to our present perception of

what is sweet by vision. That is so because we have a sense for each of the two qualities, in virtue of which

when they happen to meet in one sensible object we are aware of both contemporaneously. If it were not like

this our perception of the common qualities would always be incidental, i.e. as is the perception of Cleon's

son, where we perceive him not as Cleon's son but as white, and the white thing which we really perceive

But in the case of the common sensibles there is already in us a general sensibility which enables us to

perceive them directly; there is therefore no special sense required for their perception: if there were, our

The senses perceive each other's special objects incidentally; not because the percipient sense is this or that

special sense, but because all form a unity: this incidental perception takes place whenever sense is directed

at one and the same moment to two disparate qualities in one and the same object, e.g. to the bitterness and

the yellowness of bile, the assertion of the identity of both cannot be the act of either of the senses; hence the

It might be asked why we have more senses than one. Is it to prevent a failure to apprehend the common

sensibles, e.g. movement, magnitude, and number, which go along with the special sensibles? Had we no

sense but sight, and that sense no object but white, they would have tended to escape our notice and

everything would have merged for us into an indistinguishable identity because of the concomitance of colour

and magnitude. As it is, the fact that the common sensibles are given in the objects of more than one sense

Since it is through sense that we are aware that we are seeing or hearing, it must be either by sight that we are

aware of seeing, or by some sense other than sight. But the sense that gives us this new sensation must

perceive both sight and its object, viz. colour: so that either (1) there will be two senses both percipient of the

same sensible object, or (2) the sense must be percipient of itself. Further, even if the sense which perceives

sight were different from sight, we must either fall into an infinite regress, or we must somewhere assume a

This presents a difficulty: if to perceive by sight is just to see, and what is seen is colour (or the coloured),

then if we are to see that which sees, that which sees originally must be coloured. It is clear therefore that 'to

perceive by sight' has more than one meaning; for even when we are not seeing, it is by sight that we

discriminate darkness from light, though not in the same way as we distinguish one colour from another.

Further, in a sense even that which sees is coloured; for in each case the senseorgan is capable of receiving

the sensible object without its matter. That is why even when the sensible objects are gone the sensings and

The activity of the sensible object and that of the percipient sense is one and the same activity, and yet the

distinction between their being remains. Take as illustration actual sound and actual hearing: a man may have

hearing and yet not be hearing, and that which has a sound is not always sounding. But when that which can

hear is actively hearing and which can sound is sounding, then the actual hearing and the actual sound are

If it is true that the movement, both the acting and the being acted upon, is to be found in that which is acted

upon, both the sound and the hearing so far as it is actual must be found in that which has the faculty of

hearing; for it is in the passive factor that the actuality of the active or motive factor is realized; that is why

that which causes movement may be at rest. Now the actuality of that which can sound is just sound or

sounding, and the actuality of that which can hear is hearing or hearkening; 'sound' and 'hearing' are both

ambiguous. The same account applies to the other senses and their objects. For as

theactingandbeingactedupon is to be found in the passive, not in the active factor, so also the actuality

of the sensible object and that of the sensitive subject are both realized in the latter. But while in some cases

each aspect of the total actuality has a distinct name, e.g. sounding and hearkening, in some one or other is

nameless, e.g. the actuality of sight is called seeing, but the actuality of colour has no name: the actuality of

the faculty of taste is called tasting, but the actuality of flavour has no name. Since the actualities of the

sensible object and of the sensitive faculty are one actuality in spite of the difference between their modes of

being, actual hearing and actual sounding appear and disappear from existence at one and the same moment,

and so actual savour and actual tasting, while as potentialities one of them may exist without the other. The

earlier students of nature were mistaken in their view that without sight there was no white or black, without

taste no savour. This statement of theirs is partly true, partly false: 'sense' and 'the sensible object' are

ambiguous terms, i.e. may denote either potentialities or actualities: the statement is true of the latter, false of

If voice always implies a concord, and if the voice and the hearing of it are in one sense one and the same,

and if concord always implies a ratio, hearing as well as what is heard must be a ratio. That is why the excess

of either the sharp or the flat destroys the hearing. (So also in the case of savours excess destroys the sense of

taste, and in the case of colours excessive brightness or darkness destroys the sight, and in the case of smell

excess of strength whether in the direction of sweetness or bitterness is destructive.) This shows that the sense

That is also why the objects of sense are (1) pleasant when the sensible extremes such as acid or sweet or salt

being pure and unmixed are brought into the proper ratio; then they are pleasant: and in general what is

blended is more pleasant than the sharp or the flat alone; or, to touch, that which is capable of being either

warmed or chilled: the sense and the ratio are identical: while (2) in excess the sensible extremes are painful

Each sense then is relative to its particular group of sensible qualities: it is found in a senseorgan as such

and discriminates the differences which exist within that group; e.g. sight discriminates white and black, taste

sweet and bitter, and so in all cases. Since we also discriminate white from sweet, and indeed each sensible

quality from every other, with what do we perceive that they are different? It must be by sense; for what is

before us is sensible objects. (Hence it is also obvious that the flesh cannot be the ultimate senseorgan: if it

were, the discriminating power could not do its work without immediate contact with the object.)

Therefore (1) discrimination between white and sweet cannot be effected by two agencies which remain

separate; both the qualities discriminated must be present to something that is one and single. On any other

supposition even if I perceived sweet and you perceived white, the difference between them would be

apparent. What says that two things are different must be one; for sweet is different from white. Therefore

what asserts this difference must be selfidentical, and as what asserts, so also what thinks or perceives. That

it is not possible by means of two agencies which remain separate to discriminate two objects which are

separate, is therefore obvious; and that (it is not possible to do this in separate movements of time may be

seen' if we look at it as follows. For as what asserts the difference between the good and the bad is one and

the same, so also the time at which it asserts the one to be different and the other to be different is not

accidental to the assertion (as it is for instance when I now assert a difference but do not assert that there is

now a difference); it asserts thusboth now and that the objects are different now; the objects therefore must

be present at one and the same moment. Both the discriminating power and the time of its exercise must be

But, it may be objected, it is impossible that what is selfidentical should be moved at me and the same time

with contrary movements in so far as it is undivided, and in an undivided moment of time. For if what is

sweet be the quality perceived, it moves the sense or thought in this determinate way, while what is bitter

moves it in a contrary way, and what is white in a different way. Is it the case then that what discriminates,

though both numerically one and indivisible, is at the same time divided in its being? In one sense, it is what

is divided that perceives two separate objects at once, but in another sense it does so qua undivided; for it is

divisible in its being but spatially and numerically undivided. is not this impossible? For while it is true that

what is selfidentical and undivided may be both contraries at once potentially, it cannot be selfidentical in

its beingit must lose its unity by being put into activity. It is not possible to be at once white and black, and

therefore it must also be impossible for a thing to be affected at one and the same moment by the forms of

both, assuming it to be the case that sensation and thinking are properly so described.

The answer is that just as what is called a 'point' is, as being at once one and two, properly said to be

divisible, so here, that which discriminates is qua undivided one, and active in a single moment of time, while

so far forth as it is divisible it twice over uses the same dot at one and the same time. So far forth then as it

takes the limit as two' it discriminates two separate objects with what in a sense is divided: while so far as it

takes it as one, it does so with what is one and occupies in its activity a single moment of time.

About the principle in virtue of which we say that animals are percipient, let this discussion suffice.

There are two distinctive peculiarities by reference to which we characterize the soul (1) local movement and

(2) thinking, discriminating, and perceiving. Thinking both speculative and practical is regarded as akin to a

form of perceiving; for in the one as well as the other the soul discriminates and is cognizant of something

which is. Indeed the ancients go so far as to identify thinking and perceiving; e.g. Empedocles says 'For 'tis in

respect of what is present that man's wit is increased', and again 'Whence it befalls them from time to time to

think diverse thoughts', and Homer's phrase 'For suchlike is man's mind' means the same. They all look upon

thinking as a bodily process like perceiving, and hold that like is known as well as perceived by like, as I

explained at the beginning of our discussion. Yet they ought at the same time to have accounted for error

also; for it is more intimately connected with animal existence and the soul continues longer in the state of

error than in that of truth. They cannot escape the dilemma: either (1) whatever seems is true (and there are

some who accept this) or (2) error is contact with the unlike; for that is the opposite of the knowing of like by

But it is a received principle that error as well as knowledge in respect to contraries is one and the same.

That perceiving and practical thinking are not identical is therefore obvious; for the former is universal in the

animal world, the latter is found in only a small division of it. Further, speculative thinking is also distinct

from perceivingI mean that in which we find rightness and wrongnessrightness in prudence, knowledge,

true opinion, wrongness in their opposites; for perception of the special objects of sense is always free from

error, and is found in all animals, while it is possible to think falsely as well as truly, and thought is found

only where there is discourse of reason as well as sensibility. For imagination is different from either

perceiving or discursive thinking, though it is not found without sensation, or judgement without it. That this

activity is not the same kind of thinking as judgement is obvious. For imagining lies within our own power

whenever we wish (e.g. we can call up a picture, as in the practice of mnemonics by the use of mental

images), but in forming opinions we are not free: we cannot escape the alternative of falsehood or truth.

Further, when we think something to be fearful or threatening, emotion is immediately produced, and so too

with what is encouraging; but when we merely imagine we remain as unaffected as persons who are looking

at a painting of some dreadful or encouraging scene. Again within the field of judgement itself we find

varieties, knowledge, opinion, prudence, and their opposites; of the differences between these I must speak

Thinking is different from perceiving and is held to be in part imagination, in part judgement: we must

therefore first mark off the sphere of imagination and then speak of judgement. If then imagination is that in

virtue of which an image arises for us, excluding metaphorical uses of the term, is it a single faculty or

disposition relative to images, in virtue of which we discriminate and are either in error or not? The faculties

That imagination is not sense is clear from the following considerations: Sense is either a faculty or an

activity, e.g. sight or seeing: imagination takes place in the absence of both, as e.g. in dreams. (Again, sense

is always present, imagination not. If actual imagination and actual sensation were the same, imagination

would be found in all the brutes: this is held not to be the case; e.g. it is not found in ants or bees or grubs.

(Again, sensations are always true, imaginations are for the most part false. (Once more, even in ordinary

speech, we do not, when sense functions precisely with regard to its object, say that we imagine it to be a

man, but rather when there is some failure of accuracy in its exercise. And as we were saying before, visions

appear to us even when our eyes are shut. Neither is imagination any of the things that are never in error: e.g.

It remains therefore to see if it is opinion, for opinion may be either true or false.

But opinion involves belief (for without belief in what we opine we cannot have an opinion), and in the

brutes though we often find imagination we never find belief. Further, every opinion is accompanied by

belief, belief by conviction, and conviction by discourse of reason: while there are some of the brutes in

which we find imagination, without discourse of reason. It is clear then that imagination cannot, again, be (1)

opinion plus sensation, or (2) opinion mediated by sensation, or (3) a blend of opinion and sensation; this is

impossible both for these reasons and because the content of the supposed opinion cannot be different from

that of the sensation (I mean that imagination must be the blending of the perception of white with the

opinion that it is white: it could scarcely be a blend of the opinion that it is good with the perception that it is

white): to imagine is therefore (on this view) identical with the thinking of exactly the same as what one in

the strictest sense perceives. But what we imagine is sometimes false though our contemporaneous judgement

about it is true; e.g. we imagine the sun to be a foot in diameter though we are convinced that it is larger than

the inhabited part of the earth, and the following dilemma presents itself. Either (a while the fact has not

changed and the (observer has neither forgotten nor lost belief in the true opinion which he had, that opinion

has disappeared, or (b) if he retains it then his opinion is at once true and false. A true opinion, however,

Imagination is therefore neither any one of the states enumerated, nor compounded out of them.

But since when one thing has been set in motion another thing may be moved by it, and imagination is held to

be a movement and to be impossible without sensation, i.e. to occur in beings that are percipient and to have

for its content what can be perceived, and since movement may be produced by actual sensation and that

movement is necessarily similar in character to the sensation itself, this movement must be (1) necessarily (a)

incapable of existing apart from sensation, (b) incapable of existing except when we perceive, (such that in

virtue of its possession that in which it is found may present various phenomena both active and passive, and

The reason of the last characteristic is as follows. Perception (1) of the special objects of sense is never in

error or admits the least possible amount of falsehood. (2) That of the concomitance of the objects

concomitant with the sensible qualities comes next: in this case certainly we may be deceived; for while the

perception that there is white before us cannot be false, the perception that what is white is this or that may be

false. (3) Third comes the perception of the universal attributes which accompany the concomitant objects to

which the special sensibles attach (I mean e.g. of movement and magnitude); it is in respect of these that the

The motion which is due to the activity of sense in these three modes of its exercise will differ from the

activity of sense; (1) the first kind of derived motion is free from error while the sensation is present; (2) and

(3) the others may be erroneous whether it is present or absent, especially when the object of perception is far

off. If then imagination presents no other features than those enumerated and is what we have described, then

imagination must be a movement resulting from an actual exercise of a power of sense.

As sight is the most highly developed sense, the name Phantasia (imagination) has been formed from Phaos

And because imaginations remain in the organs of sense and resemble sensations, animals in their actions are

largely guided by them, some (i.e. the brutes) because of the nonexistence in them of mind, others (i.e. men)

because of the temporary eclipse in them of mind by feeling or disease or sleep.

Turning now to the part of the soul with which the soul knows and thinks (whether this is separable from the

others in definition only, or spatially as well) we have to inquire (1) what differentiates this part, and (2) how

If thinking is like perceiving, it must be either a process in which the soul is acted upon by what is capable of

being thought, or a process different from but analogous to that. The thinking part of the soul must therefore

be, while impassible, capable of receiving the form of an object; that is, must be potentially identical in

character with its object without being the object. Mind must be related to what is thinkable, as sense is to

Therefore, since everything is a possible object of thought, mind in order, as Anaxagoras says, to dominate,

that is, to know, must be pure from all admixture; for the copresence of what is alien to its nature is a

hindrance and a block: it follows that it too, like the sensitive part, can have no nature of its own, other than

that of having a certain capacity. Thus that in the soul which is called mind (by mind I mean that whereby the

soul thinks and judges) is, before it thinks, not actually any real thing. For this reason it cannot reasonably be

regarded as blended with the body: if so, it would acquire some quality, e.g. warmth or cold, or even have an

organ like the sensitive faculty: as it is, it has none. It was a good idea to call the soul 'the place of forms',

though (1) this description holds only of the intellective soul, and (2) even this is the forms only potentially,

Observation of the senseorgans and their employment reveals a distinction between the impassibility of the

sensitive and that of the intellective faculty. After strong stimulation of a sense we are less able to exercise it

than before, as e.g. in the case of a loud sound we cannot hear easily immediately after, or in the case of a

bright colour or a powerful odour we cannot see or smell, but in the case of mind thought about an object that

is highly intelligible renders it more and not less able afterwards to think objects that are less intelligible: the

reason is that while the faculty of sensation is dependent upon the body, mind is separable from it.

Once the mind has become each set of its possible objects, as a man of science has, when this phrase is used

of one who is actually a man of science (this happens when he is now able to exercise the power on his own

initiative), its condition is still one of potentiality, but in a different sense from the potentiality which

preceded the acquisition of knowledge by learning or discovery: the mind too is then able to think itself.

Since we can distinguish between a spatial magnitude and what it is to be such, and between water and what

it is to be water, and so in many other cases (though not in all; for in certain cases the thing and its form are

identical), flesh and what it is to be flesh are discriminated either by different faculties, or by the same faculty

in two different states: for flesh necessarily involves matter and is like what is snubnosed, a this in a this.

Now it is by means of the sensitive faculty that we discriminate the hot and the cold, i.e. the factors which

combined in a certain ratio constitute flesh: the essential character of flesh is apprehended by something

different either wholly separate from the sensitive faculty or related to it as a bent line to the same line when

Again in the case of abstract objects what is straight is analogous to what is snubnosed; for it necessarily

implies a continuum as its matter: its constitutive essence is different, if we may distinguish between

straightness and what is straight: let us take it to be twoness. It must be apprehended, therefore, by a

different power or by the same power in a different state. To sum up, in so far as the realities it knows are

capable of being separated from their matter, so it is also with the powers of mind.

The problem might be suggested: if thinking is a passive affection, then if mind is simple and impassible and

has nothing in common with anything else, as Anaxagoras says, how can it come to think at all? For

interaction between two factors is held to require a precedent community of nature between the factors. Again

it might be asked, is mind a possible object of thought to itself? For if mind is thinkable per se and what is

thinkable is in kind one and the same, then either (a) mind will belong to everything, or (b) mind will contain

some element common to it with all other realities which makes them all thinkable.

(1) Have not we already disposed of the difficulty about interaction involving a common element, when we

said that mind is in a sense potentially whatever is thinkable, though actually it is nothing until it has thought?

What it thinks must be in it just as characters may be said to be on a writingtablet on which as yet nothing

(Mind is itself thinkable in exactly the same way as its objects are. For (a) in the case of objects which

involve no matter, what thinks and what is thought are identical; for speculative knowledge and its object are

identical. (Why mind is not always thinking we must consider later.) (b) In the case of those which contain

matter each of the objects of thought is only potentially present. It follows that while they will not have mind

in them (for mind is a potentiality of them only in so far as they are capable of being disengaged from matter)

Since in every class of things, as in nature as a whole, we find two factors involved, (1) a matter which is

potentially all the particulars included in the class, (2) a cause which is productive in the sense that it makes

them all (the latter standing to the former, as e.g. an art to its material), these distinct elements must likewise

And in fact mind as we have described it is what it is what it is by virtue of becoming all things, while there

is another which is what it is by virtue of making all things: this is a sort of positive state like light; for in a

Mind in this sense of it is separable, impassible, unmixed, since it is in its essential nature activity (for always

the active is superior to the passive factor, the originating force to the matter which it forms).

Actual knowledge is identical with its object: in the individual, potential knowledge is in time prior to actual

knowledge, but in the universe as a whole it is not prior even in time. Mind is not at one time knowing and at

another not. When mind is set free from its present conditions it appears as just what it is and nothing more:

this alone is immortal and eternal (we do not, however, remember its former activity because, while mind in

this sense is impassible, mind as passive is destructible), and without it nothing thinks.

The thinking then of the simple objects of thought is found in those cases where falsehood is impossible:

where the alternative of true or false applies, there we always find a putting together of objects of thought in a

quasiunity. As Empedocles said that 'where heads of many a creature sprouted without necks' they

afterwards by Love's power were combined, so here too objects of thought which were given separate are

combined, e.g. 'incommensurate' and 'diagonal': if the combination be of objects past or future the

combination of thought includes in its content the date. For falsehood always involves a synthesis; for even if

you assert that what is white is not white you have included not white in a synthesis. It is possible also to call

all these cases division as well as combination. However that may be, there is not only the true or false

assertion that Cleon is white but also the true or false assertion that he was or will he white. In each and every

Since the word 'simple' has two senses, i.e. may mean either (a) 'not capable of being divided' or (b) 'not

actually divided', there is nothing to prevent mind from knowing what is undivided, e.g. when it apprehends a

length (which is actually undivided) and that in an undivided time; for the time is divided or undivided in the

same manner as the line. It is not possible, then, to tell what part of the line it was apprehending in each half

of the time: the object has no actual parts until it has been divided: if in thought you think each half

separately, then by the same act you divide the time also, the halflines becoming as it were new wholes of

length. But if you think it as a whole consisting of these two possible parts, then also you think it in a time

which corresponds to both parts together. (But what is not quantitatively but qualitatively simple is thought in

But that which mind thinks and the time in which it thinks are in this case divisible only incidentally and not

as such. For in them too there is something indivisible (though, it may be, not isolable) which gives unity to

the time and the whole of length; and this is found equally in every continuum whether temporal or spatial.

Points and similar instances of things that divide, themselves being indivisible, are realized in consciousness

A similar account may be given of all other cases, e.g. how evil or black is cognized; they are cognized, in a

sense, by means of their contraries. That which cognizes must have an element of potentiality in its being,

and one of the contraries must be in it. But if there is anything that has no contrary, then it knows itself and is

Assertion is the saying of something concerning something, e.g. affirmation, and is in every case either true

or false: this is not always the case with mind: the thinking of the definition in the sense of the constitutive

essence is never in error nor is it the assertion of something concerning something, but, just as while the

seeing of the special object of sight can never be in error, the belief that the white object seen is a man may

Actual knowledge is identical with its object: potential knowledge in the individual is in time prior to actual

knowledge but in the universe it has no priority even in time; for all things that come into being arise from

what actually is. In the case of sense clearly the sensitive faculty already was potentially what the object

makes it to be actually; the faculty is not affected or altered. This must therefore be a different kind from

movement; for movement is, as we saw, an activity of what is imperfect, activity in the unqualified sense, i.e.

To perceive then is like bare asserting or knowing; but when the object is pleasant or painful, the soul makes

a quasiaffirmation or negation, and pursues or avoids the object. To feel pleasure or pain is to act with the

sensitive mean towards what is good or bad as such. Both avoidance and appetite when actual are identical

with this: the faculty of appetite and avoidance are not different, either from one another or from the faculty

To the thinking soul images serve as if they were contents of perception (and when it asserts or denies them

to be good or bad it avoids or pursues them). That is why the soul never thinks without an image. The process

is like that in which the air modifies the pupil in this or that way and the pupil transmits the modification to

some third thing (and similarly in hearing), while the ultimate point of arrival is one, a single mean, with

With what part of itself the soul discriminates sweet from hot I have explained before and must now describe

again as follows: That with which it does so is a sort of unity, but in the way just mentioned, i.e. as a

connecting term. And the two faculties it connects, being one by analogy and numerically, are each to each as

the qualities discerned are to one another (for what difference does it make whether we raise the problem of

discrimination between disparates or between contraries, e.g. white and black?). Let then C be to D as is to B:

it follows alternando that C: A:: D: B. If then C and D belong to one subject, the case will be the same with

them as with and B; and B form a single identity with different modes of being; so too will the former pair.

The faculty of thinking then thinks the forms in the images, and as in the former case what is to be pursued or

avoided is marked out for it, so where there is no sensation and it is engaged upon the images it is moved to

pursuit or avoidance. E.g.. perceiving by sense that the beacon is fire, it recognizes in virtue of the general

faculty of sense that it signifies an enemy, because it sees it moving; but sometimes by means of the images

or thoughts which are within the soul, just as if it were seeing, it calculates and deliberates what is to come by

reference to what is present; and when it makes a pronouncement, as in the case of sensation it pronounces

the object to be pleasant or painful, in this case it avoids or persues and so generally in cases of action.

That too which involves no action, i.e. that which is true or false, is in the same province with what is good or

bad: yet they differ in this, that the one set imply and the other do not a reference to a particular person.

The socalled abstract objects the mind thinks just as, if one had thought of the snubnosed not as snubnosed

but as hollow, one would have thought of an actuality without the flesh in which it is embodied: it is thus that

the mind when it is thinking the objects of Mathematics thinks as separate elements which do not exist

separate. In every case the mind which is actively thinking is the objects which it thinks. Whether it is

possible for it while not existing separate from spatial conditions to think anything that is separate, or not, we

Let us now summarize our results about soul, and repeat that the soul is in a way all existing things; for

existing things are either sensible or thinkable, and knowledge is in a way what is knowable, and sensation is

Knowledge and sensation are divided to correspond with the realities, potential knowledge and sensation

answering to potentialities, actual knowledge and sensation to actualities. Within the soul the faculties of

knowledge and sensation are potentially these objects, the one what is knowable, the other what is sensible.

They must be either the things themselves or their forms. The former alternative is of course impossible: it is

It follows that the soul is analogous to the hand; for as the hand is a tool of tools, so the mind is the form of

Since according to common agreement there is nothing outside and separate in existence from sensible spatial

magnitudes, the objects of thought are in the sensible forms, viz. both the abstract objects and all the states

and affections of sensible things. Hence (1) no one can learn or understand anything in the absence of sense,

and (when the mind is actively aware of anything it is necessarily aware of it along with an image; for images

Imagination is different from assertion and denial; for what is true or false involves a synthesis of concepts.

In what will the primary concepts differ from images? Must we not say that neither these nor even our other

The soul of animals is characterized by two faculties, (a) the faculty of discrimination which is the work of

thought and sense, and (b) the faculty of originating local movement. Sense and mind we have now

sufficiently examined. Let us next consider what it is in the soul which originates movement. Is it a single

part of the soul separate either spatially or in definition? Or is it the soul as a whole? If it is a part, is that part

different from those usually distinguished or already mentioned by us, or is it one of them? The problem at

once presents itself, in what sense we are to speak of parts of the soul, or how many we should distinguish.

For in a sense there is an infinity of parts: it is not enough to distinguish, with some thinkers, the calculative,

the passionate, and the desiderative, or with others the rational and the irrational; for if we take the dividing

lines followed by these thinkers we shall find parts far more distinctly separated from one another than these,

namely those we have just mentioned: (1) the nutritive, which belongs both to plants and to all animals, and

(2) the sensitive, which cannot easily be classed as either irrational or rational; further (3) the imaginative,

which is, in its being, different from all, while it is very hard to say with which of the others it is the same or

not the same, supposing we determine to posit separate parts in the soul; and lastly (4) the appetitive, which

would seem to be distinct both in definition and in power from all hitherto enumerated.

It is absurd to break up the lastmentioned faculty: as these thinkers do, for wish is found in the calculative

part and desire and passion in the irrational; and if the soul is tripartite appetite will be found in all three

parts. Turning our attention to the present object of discussion, let us ask what that is which originates local

The movement of growth and decay, being found in all living things, must be attributed to the faculty of

reproduction and nutrition, which is common to all: inspiration and expiration, sleep and waking, we must

consider later: these too present much difficulty: at present we must consider local movement, asking what it

That it is not the nutritive faculty is obvious; for this kind of movement is always for an end and is

accompanied either by imagination or by appetite; for no animal moves except by compulsion unless it has an

impulse towards or away from an object. Further, if it were the nutritive faculty, even plants would have been

capable of originating such movement and would have possessed the organs necessary to carry it out.

Similarly it cannot be the sensitive faculty either; for there are many animals which have sensibility but

If then Nature never makes anything without a purpose and never leaves out what is necessary (except in the

case of mutilated or imperfect growths; and that here we have neither mutilation nor imperfection may be

argued from the facts that such animals (a) can reproduce their species and (b) rise to completeness of nature

and decay to an end), it follows that, had they been capable of originating forward movement, they would

have possessed the organs necessary for that purpose. Further, neither can the calculative faculty or what is

called 'mind' be the cause of such movement; for mind as speculative never thinks what is practicable, it

never says anything about an object to be avoided or pursued, while this movement is always in something

which is avoiding or pursuing an object. No, not even when it is aware of such an object does it at once

enjoin pursuit or avoidance of it; e.g. the mind often thinks of something terrifying or pleasant without

enjoining the emotion of fear. It is the heart that is moved (or in the case of a pleasant object some other part).

Further, even when the mind does command and thought bids us pursue or avoid something, sometimes no

movement is produced; we act in accordance with desire, as in the case of moral weakness. And, generally,

we observe that the possessor of medical knowledge is not necessarily healing, which shows that something

else is required to produce action in accordance with knowledge; the knowledge alone is not the cause.

Lastly, appetite too is incompetent to account fully for movement; for those who successfully resist

temptation have appetite and desire and yet follow mind and refuse to enact that for which they have appetite.

These two at all events appear to be sources of movement: appetite and mind (if one may venture to regard

imagination as a kind of thinking; for many men follow their imaginations contrary to knowledge, and in all

animals other than man there is no thinking or calculation but only imagination).

Both of these then are capable of originating local movement, mind and appetite: (1) mind, that is, which

calculates means to an end, i.e. mind practical (it differs from mind speculative in the character of its end);

while (2) appetite is in every form of it relative to an end: for that which is the object of appetite is the

stimulant of mind practical; and that which is last in the process of thinking is the beginning of the action. It

follows that there is a justification for regarding these two as the sources of movement, i.e. appetite and

practical thought; for the object of appetite starts a movement and as a result of that thought gives rise to

movement, the object of appetite being it a source of stimulation. So too when imagination originates

That which moves therefore is a single faculty and the faculty of appetite; for if there had been two sources of

movementmind and appetitethey would have produced movement in virtue of some common character. As

it is, mind is never found producing movement without appetite (for wish is a form of appetite; and when

movement is produced according to calculation it is also according to wish), but appetite can originate

movement contrary to calculation, for desire is a form of appetite. Now mind is always right, but appetite and

imagination may be either right or wrong. That is why, though in any case it is the object of appetite which

originates movement, this object may be either the real or the apparent good. To produce movement the

object must be more than this: it must be good that can be brought into being by action; and only what can be

otherwise than as it is can thus be brought into being. That then such a power in the soul as has been

described, i.e. that called appetite, originates movement is clear. Those who distinguish parts in the soul, if

they distinguish and divide in accordance with differences of power, find themselves with a very large

number of parts, a nutritive, a sensitive, an intellective, a deliberative, and now an appetitive part; for these

Since appetites run counter to one another, which happens when a principle of reason and a desire are

contrary and is possible only in beings with a sense of time (for while mind bids us hold back because of

what is future, desire is influenced by what is just at hand: a pleasant object which is just at hand presents

itself as both pleasant and good, without condition in either case, because of want of foresight into what is

farther away in time), it follows that while that which originates movement must be specifically one, viz. the

faculty of appetite as such (or rather farthest back of all the object of that faculty; for it is it that itself

remaining unmoved originates the movement by being apprehended in thought or imagination), the things

All movement involves three factors, (1) that which originates the movement, (2) that by means of which it

originates it, and (3) that which is moved. The expression 'that which originates the movement' is ambiguous:

it may mean either (a) something which itself is unmoved or (b) that which at once moves and is moved. Here

that which moves without itself being moved is the realizable good, that which at once moves and is moved is

the faculty of appetite (for that which is influenced by appetite so far as it is actually so influenced is set in

movement, and appetite in the sense of actual appetite is a kind of movement), while that which is in motion

is the animal. The instrument which appetite employs to produce movement is no longer psychical but

bodily: hence the examination of it falls within the province of the functions common to body and soul. To

state the matter summarily at present, that which is the instrument in the production of movement is to be

found where a beginning and an end coincide as e.g. in a ball and socket joint; for there the convex and the

concave sides are respectively an end and a beginning (that is why while the one remains at rest, the other is

moved): they are separate in definition but not separable spatially. For everything is moved by pushing and

pulling. Hence just as in the case of a wheel, so here there must be a point which remains at rest, and from

To sum up, then, and repeat what I have said, inasmuch as an animal is capable of appetite it is capable of

selfmovement; it is not capable of appetite without possessing imagination; and all imagination is either (1)

calculative or (2) sensitive. In the latter an animals, and not only man, partake.

We must consider also in the case of imperfect animals, sc. those which have no sense but touch, what it is

that in them originates movement. Can they have imagination or not? or desire? Clearly they have feelings of

pleasure and pain, and if they have these they must have desire. But how can they have imagination? Must

not we say that, as their movements are indefinite, they have imagination and desire, but indefinitely?

Sensitive imagination, as we have said, is found in all animals, deliberative imagination only in those that are

calculative: for whether this or that shall be enacted is already a task requiring calculation; and there must be

a single standard to measure by, for that is pursued which is greater. It follows that what acts in this way must

This is the reason why imagination is held not to involve opinion, in that it does not involve opinion based on

inference, though opinion involves imagination. Hence appetite contains no deliberative element. Sometimes

it overpowers wish and sets it in movement: at times wish acts thus upon appetite, like one sphere imparting

its movement to another, or appetite acts thus upon appetite, i.e. in the condition of moral weakness (though

by nature the higher faculty is always more authoritative and gives rise to movement). Thus three modes of

The faculty of knowing is never moved but remains at rest. Since the one premiss or judgement is universal

and the other deals with the particular (for the first tells us that such and such a kind of man should do such

and such a kind of act, and the second that this is an act of the kind meant, and I a person of the type

intended), it is the latter opinion that really originates movement, not the universal; or rather it is both, but the

one does so while it remains in a state more like rest, while the other partakes in movement.

The nutritive soul then must be possessed by everything that is alive, and every such thing is endowed with

soul from its birth to its death. For what has been born must grow, reach maturity, and decayall of which are

impossible without nutrition. Therefore the nutritive faculty must be found in everything that grows and

But sensation need not be found in all things that live. For it is impossible for touch to belong either (1) to

those whose body is uncompounded or (2) to those which are incapable of taking in the forms without their

But animals must be endowed with sensation, since Nature does nothing in vain. For all things that exist by

Nature are means to an end, or will be concomitants of means to an end. Every body capable of forward

movement would, if unendowed with sensation, perish and fail to reach its end, which is the aim of Nature;

for how could it obtain nutriment? Stationary living things, it is true, have as their nutriment that from which

they have arisen; but it is not possible that a body which is not stationary but produced by generation should

have a soul and a discerning mind without also having sensation. (Nor yet even if it were not produced by

generation. Why should it not have sensation? Because it were better so either for the body or for the soul?

But clearly it would not be better for either: the absence of sensation will not enable the one to think better or

the other to exist better.) Therefore no body which is not stationary has soul without sensation.

But if a body has sensation, it must be either simple or compound. And simple it cannot be; for then it could

not have touch, which is indispensable. This is clear from what follows. An animal is a body with soul in it:

every body is tangible, i.e. perceptible by touch; hence necessarily, if an animal is to survive, its body must

have tactual sensation. All the other senses, e.g. smell, sight, hearing, apprehend through media; but where

there is immediate contact the animal, if it has no sensation, will be unable to avoid some things and take

others, and so will find it impossible to survive. That is why taste also is a sort of touch; it is relative to

nutriment, which is just tangible body; whereas sound, colour, and odour are innutritious, and further neither

grow nor decay. Hence it is that taste also must be a sort of touch, because it is the sense for what is tangible

Both these senses, then, are indispensable to the animal, and it is clear that without touch it is impossible for

an animal to be. All the other senses subserve wellbeing and for that very reason belong not to any and

every kind of animal, but only to some, e.g. those capable of forward movement must have them; for, if they

are to survive, they must perceive not only by immediate contact but also at a distance from the object. This

will be possible if they can perceive through a medium, the medium being affected and moved by the

perceptible object, and the animal by the medium. just as that which produces local movement causes a

change extending to a certain point, and that which gave an impulse causes another to produce a new impulse

so that the movement traverses a medium the first mover impelling without being impelled, the last moved

being impelled without impelling, while the medium (or media, for there are many) is bothso is it also in the

case of alteration, except that the agent produces produces it without the patient's changing its place. Thus if

an object is dipped into wax, the movement goes on until submersion has taken place, and in stone it goes no

distance at all, while in water the disturbance goes far beyond the object dipped: in air the disturbance is

propagated farthest of all, the air acting and being acted upon, so long as it maintains an unbroken unity. That

is why in the case of reflection it is better, instead of saying that the sight issues from the eye and is reflected,

to say that the air, so long as it remains one, is affected by the shape and colour. On a smooth surface the air

possesses unity; hence it is that it in turn sets the sight in motion, just as if the impression on the wax were

It is clear that the body of an animal cannot be simple, i.e. consist of one element such as fire or air. For

without touch it is impossible to have any other sense; for every body that has soul in it must, as we have

said, be capable of touch. All the other elements with the exception of earth can constitute organs of sense,

but all of them bring about perception only through something else, viz. through the media. Touch takes place

by direct contact with its objects, whence also its name. All the other organs of sense, no doubt, perceive by

contact, only the contact is mediate: touch alone perceives by immediate contact. Consequently no animal

Nor can it consist solely of earth. For touch is as it were a mean between all tangible qualities, and its organ is

capable of receiving not only all the specific qualities which characterize earth, but also the hot and the cold

and all other tangible qualities whatsoever. That is why we have no sensation by means of bones, hair,

because they consist of earth. So too plants, because they consist of earth, have no sensation. Without touch

there can be no other sense, and the organ of touch cannot consist of earth or of any other single element.

It is evident, therefore, that the loss of this one sense alone must bring about the death of an animal. For as on

the one hand nothing which is not an animal can have this sense, so on the other it is the only one which is

indispensably necessary to what is an animal. This explains, further, the following difference between the

other senses and touch. In the case of all the others excess of intensity in the qualities which they apprehend,

i.e. excess of intensity in colour, sound, and smell, destroys not the but only the organs of the sense (except

incidentally, as when the sound is accompanied by an impact or shock, or where through the objects of sight

or of smell certain other things are set in motion, which destroy by contact); flavour also destroys only in so

far as it is at the same time tangible. But excess of intensity in tangible qualities, e.g. heat, cold, or hardness,

destroys the animal itself. As in the case of every sensible quality excess destroys the organ, so here what is

tangible destroys touch, which is the essential mark of life; for it has been shown that without touch it is

impossible for an animal to be. That is why excess in intensity of tangible qualities destroys not merely the

organ, but the animal itself, because this is the only sense which it must have.

All the other senses are necessary to animals, as we have said, not for their being, but for their wellbeing.

Such, e.g. is sight, which, since it lives in air or water, or generally in what is pellucid, it must have in order

to see, and taste because of what is pleasant or painful to it, in order that it may perceive these qualities in its

nutriment and so may desire to be set in motion, and hearing that it may have communication made to it, and