by Aristotle
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 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.
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 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 an animals, and not only man, partake.
11
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 be able to make a unity out of several images.
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
movement are possible.
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.
12
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 decay-all
of which are impossible without nutrition. Therefore the nutritive
faculty must be found in everything that grows and decays.
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 matter.
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 and nutritious.
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 well-being 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 both-so 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 transmitted as far as the wax extends.
13
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
&nbs
p; perceives by immediate contact. Consequently no animal body can
consist of these other elements.
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, c., 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,