From
De Anima (On the Soul)
Available at: http://psychclassics.yorku.ca/Aristotle/De-anima/
Chapter 1 -- Let the foregoing (Book I) suffice as our account
of the views [412a] 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, endeavoring 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 related to one another as e.g. knowledge to the
exercise of knowledge.
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 self-nutrition and growth (with its correlative
decay). It follows that every natural body which has life in it is a substance
in the sense of a composite.
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
[412b] 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 animal-sight 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 name -- it 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 [413a] 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 animal.
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 of the ship.
This must suffice as
our sketch or outline determination of the nature of soul.
Chapter 2 -- 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 starting-point 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 nutriment.
This power of
self-nutrition can be isolated from the other powers mentioned, but not they
from it -- in 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 [413b] 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 not merely living things.
The primary form of
sense is touch, which belongs to all animals. just as the power of
self-nutrition can be isolated from touch and sensation generally, so touch can
be isolated from all other forms of sense. (By the power of self-nutrition 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 self-nutrition, sensation,
thinking, and motivity.
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 desire.
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 [414a]
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 matter -- knowledge 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 cannot be 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
that possesses a potentiality of being besouled.
Chapter 3 -- 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 [414b] 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, &c., 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 cases -- figures and living beings -- constitute
a series, each successive term of which potentially contains its predecessor,
e.g. the square the triangle, the sensory power the self-nutritive. 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 [415a] subject of later examination. But the facts are
that the power of perception is never found apart from the power of
self-nutrition, while in plants the 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 beings -- a small minority -- possess calculation and thought, for
(among mortal beings) those which possess calculation have all the other powers
above mentioned, while the converse does not hold -- indeed some live by
imagination alone, while others have not even imagination. The mind that knows
with immediate intuition presents a different problem.
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 for the most appropriate definition.
Chapter 4 -- 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, &c. 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 what is perceptible, or with what is intelligible.
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 food-reproduction, 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 [415b] 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 self-same individual but continues its
existence in something like itself -- not numerically but specifically one.
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 movement, it is (b) the end, it is
(c) the essence of the whole living body.
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 what has a share of
soul in it.
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 [416a] 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 it -- not 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; [416b] there is a change in the carpenter but it is merely
a change from not-working 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 a certain sense we may say that both parties are right, both
wrong.
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 'this-somewhat' 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 substance is a
self-generation but only a self-maintenance. 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 deprived of food, it must cease to be.
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 place.
Chapter 5 -- 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. [417a] 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 activity -- an 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 and during the change the two factors are unlike, after
it like.
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 knowledge -- he 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 [417b] sense or grammar to their active exercise. The two kinds
of transition are distinct.
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
quite different sense from the usual meaning.
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 from potentiality in the
direction of fixity or nature.
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, &c., 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
sensible on the same ground, viz. that the sensible objects are individual and
external.
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
[418a] 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.
Chapter 6 -- 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 and by sight.
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 kind -- that of special
objects of the several senses -- constitute 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.
Chapter 7 -- 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; [418b] 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 is.
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 activity
-- the 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 something which is one
and the same with the substance in question.
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 of
that.
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 [419a] 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
transparent is just light.
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 between -- if 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 that makes what is potentially transparent actually transparent.
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 smell -- I
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 [419a] that breathe, perceive smells only when they breathe air
in. The explanation of this too will be given later. ...
... Chapter 3 -- 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 [427b] 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 like.
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 perceiving -- I mean
that in which we find rightness and wrongness -- rightness 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 elsewhere.
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
[428a] 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 in virtue of which we do this are sense,
opinion, science, intelligence.
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.
knowledge or intelligence; for imagination may be false.
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 [428b] 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, becomes false only when the
fact alters without being noticed.
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 (such that it may be either true or
false.
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 greatest amount of sense-illusion is possible.
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 [429a] sense.
As sight is the most
highly developed sense, the name Phantasia (imagination) has been formed from
Phaos (light) because it is not possible to see without light. 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
non-existence in them of mind, others (i.e. men) because of the temporary
eclipse in them of mind by feeling or disease or sleep.
About imagination,
what it is and why it exists, let so much suffice.
Chapter 4 -- 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 thinking can take place.
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 what is sensible.
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
co-presence 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, not actually.
Observation of the
sense-organs and their employment reveals a distinction between the
impassibility of the sensitive and that of the intellective faculty. After
strong [429b] 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 snub-nosed, 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 it has
been straightened out.
Again in the case of
abstract objects what is straight is analogous to what is snub-nosed; 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 two-ness. 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 [430a] writing tablet
on which as yet nothing actually stands written: this is exactly what happens
with mind.
(2) 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) mind may yet be
thinkable. ...
... Chapter 8 -- 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 in a way what is sensible: in what way we must inquire. 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 not the stone which is present in
the soul but its form.
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 [432a] forms and sense the form of sensible things.
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 are like sensuous contents except in that
they contain no matter).
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 concepts are images,
though they necessarily involve them?
Chapter 9 -- 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, [432b] 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 last-mentioned 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 movement
of the animal.
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 is that originates
forward movement in the animal.
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 remain fast and immovable
throughout their lives.
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
[433a] 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.
Chapter 10 -- 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 movement, it necessarily involves
appetite.
That which moves
therefore is a single faculty and the faculty of appetite; for if there had
been two sources of movement -- mind and appetite -- they 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
[433b] 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 are more different from one
another than the faculties of desire and passion.
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 that originate movement are numerically
many.
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
that point the movement must originate.
To sum up, then, and
repeat what I have said, inasmuch as an animal is capable of appetite it is
capable of self-movement; it is not capable of appetite without possessing
imagination; and all imagination is either (1) calculative or (2) sensitive. In
the latter all animals, and not only man, partake.