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then moves； itself being unmoved； whereas desire and its faculty are
moved and so move。 But it is not necessary for the last in the chain
of things moved to move something else； wherefore it is plainly
reasonable that motion in place should be the last of what happens
in the region of things happening； since the living creature is
moved and goes forward by reason of desire or purpose； when some
alteration has been set going on the occasion of sensation or
imagination。
7
But how is it that thought （viz。 sense； imagination； and thought
proper） is sometimes followed by action； sometimes not； sometimes by
movement； sometimes not？ What happens seems parallel to the case of
thinking and inferring about the immovable objects of science。 There
the end is the truth seen （for； when one conceives the two
premisses； one at once conceives and comprehends the conclusion）；
but here the two premisses result in a conclusion which is an
action… for example； one conceives that every man ought to walk； one
is a man oneself： straightway one walks； or that； in this case； no man
should walk； one is a man： straightway one remains at rest。 And one so
acts in the two cases provided that there is nothing in the one case
to compel or in the other to prevent。 Again； I ought to create a good；
a house is good： straightway I make a house。 I need a covering； a coat
is a covering： I need a coat。 What I need I ought to make； I need a
coat： I make a coat。 And the conclusion I must make a coat is an
action。 And the action goes back to the beginning or first step。 If
there is to be a coat； one must first have B； and if B then A； so
one gets A to begin with。 Now that the action is the conclusion is
clear。 But the premisses of action are of two kinds； of the good and
of the possible。
And as in some cases of speculative inquiry we suppress one
premise so here the mind does not stop to consider at all an obvious
minor premise； for example if walking is good for man； one does not
dwell upon the minor 'I am a man'。 And so what we do without
reflection； we do quickly。 For when a man actualizes himself in
relation to his object either by perceiving； or imagining or
conceiving it； what he desires he does at once。 For the actualizing of
desire is a substitute for inquiry or reflection。 I want to drink；
says appetite； this is drink； says sense or imagination or mind：
straightway I drink。 In this way living creatures are impelled to move
and to act； and desire is the last or immediate cause of movement； and
desire arises after perception or after imagination and conception。
And things that desire to act now create and now act under the
influence of appetite or impulse or of desire or wish。
The movements of animals may be compared with those of automatic
puppets； which are set going on the occasion of a tiny movement； the
levers are released； and strike the twisted strings against one
another； or with the toy wagon。 For the child mounts on it and moves
it straight forward； and then again it is moved in a circle owing to
its wheels being of unequal diameter （the smaller acts like a centre
on the same principle as the cylinders）。 Animals have parts of a
similar kind； their organs； the sinewy tendons to wit and the bones；
the bones are like the wooden levers in the automaton； and the iron；
the tendons are like the strings； for when these are tightened or
leased movement begins。 However； in the automata and the toy wagon
there is no change of quality； though if the inner wheels became
smaller and greater by turns there would be the same circular movement
set up。 In an animal the same part has the power of becoming now
larger and now smaller； and changing its form； as the parts increase
by warmth and again contract by cold and change their quality。 This
change of quality is caused by imaginations and sensations and by
ideas。 Sensations are obviously a form of change of quality； and
imagination and conception have the same effect as the objects so
imagined and conceived For in a measure the form conceived be it of
hot or cold or pleasant or fearful is like what the actual objects
would be； and so we shudder and are frightened at a mere idea。 Now all
these affections involve changes of quality； and with those changes
some parts of the body enlarge； others grow smaller。 And it is not
hard to see that a small change occurring at the centre makes great
and numerous changes at the circumference； just as by shifting the
rudder a hair's breadth you get a wide deviation at the prow。 And
further； when by reason of heat or cold or some kindred affection a
change is set up in the region of the heart； even in an
imperceptibly small part of the heart； it produces a vast difference
in the periphery of the body；… blushing； let us say； or turning white；
goose…skin and shivers and their opposites。
8
But to return； the object we pursue or avoid in the field of
action is； as has been explained； the original of movement； and upon
the conception and imagination of this there necessarily follows a
change in the temperature of the body。 For what is painful we avoid；
what is pleasing we pursue。 We are； however； unconscious of what
happens in the minute parts； still anything painful or pleasing is
generally speaking accompanied by a definite change of temperature
in the body。 One may see this by considering the affections。 Blind
courage and panic fears； erotic motions； and the rest of the corporeal
affections； pleasant and painful； are all accompanied by a change of
temperature； some in a particular member； others in the body
generally。 So； memories and anticipations； using as it were the
reflected images of these pleasures and pains； are now more and now
less causes of the same changes of temperature。 And so we see the
reason of nature's handiwork in the inward parts； and in the centres
of movement of the organic members； they change from solid to moist；
and from moist to solid； from soft to hard and vice versa。 And so when
these are affected in this way； and when besides the passive and
active have the constitution we have many times described； as often as
it comes to pass that one is active and the other passive； and neither
of them falls short of the elements of its essence； straightway one
acts and the other responds。 And on this account thinking that one
ought to go and going are virtually simultaneous； unless there be
something else to hinder action。 The organic parts are suitably
prepared by the affections； these again by desire； and desire by
imagination。 Imagination in its turn depends either upon conception or
sense…perception。 And the simultaneity and speed are due to the
natural correspondence of the active and passive。
However； that which first moves the animal organism must be
situate in a definite original。 Now we have said that a joint is the
beginning of one part of a limb； the end of another。 And so nature
employs it sometimes as one； sometimes as two。 When movement arises
from a joint； one of the extreme points must remain at rest； and the
other be moved （for as we explained above the mover must support
itself against a point at rest）； accordingly； in the case of the
elbow…joint； the last point of the forearm is moved but does not
move anything； while； in the flexion； one point of the elbow； which
lies in the whole forearm that is being moved； is moved； but there
must also be a point which is unmoved； and this is our meaning when we
speak of a point which is in potency one； but which becomes two in
actual exercise。 Now if the arm were the living animal； somewhere in
its elbow…joint would be situate the original seat of the moving soul。