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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。
Since； however； it is possible for a lifeless thing to be so related
to the hand as the forearm is to the upper （for example； when a man
moves a stick in his hand）； it is evident that the soul； the
original of movement； could not lie in either of the two extreme
points； neither； that is； in the last point of the stick which is
moved； nor in the original point which causes movement。 For the
stick too has an end point and an originative point by reference to
the hand。 Accordingly； this example shows that the moving original
which derives from the soul is not in the stick and if not； then not
in the hand； for a precisely similar relation obtains between the hand
and the wrist； as between the wrist and the elbow。 In this matter it
makes no difference whether the part is a continuous part of the
body or not； the stick may be looked at as a detached part of the
whole。 It follows then of necessity that the original cannot lie in
any individual origin which is the end of another member； even
though there may lie another part outside the one in question。 For
example； relatively to the end point of the stick the hand is the
original； but the original of the hand's movement is in the wrist。 And
so if the true original is not in the hand； be…there is still
something higher up； neither is the true original in the wrist； for
once more if the elbow is at rest the whole part below it can be moved
as a continuous whole。
9
Now since the left and the right sides are symmetrical； and these
opposites are moved simultaneously； it cannot be that the left is
moved by the right remaining stationary； nor vice versa； the
original must always be in what lies above both。 Therefore； the
original seat of the moving soul must be in that which lies in the
middle； for of both extremes the middle is the limiting point； and
this is similarly related to the movements from above ＇and below；＇
those that is from the head； and to the bones which spring from the
spinal column； in creatures that have a spinal column。
And this is a reasonable arrangement。 For the sensorium is in our
opinion in the centre too； and so； if the region of the original of
movement is altered in structure through sense…perception and thus
changes； it carries with it the parts that depend upon it and they too
are extended or contracted； and in this way the movement of the
creature necessarily follows。 And the middle of the body must needs be
in potency one but in action more than one； for the limbs are moved
simultaneously from the original seat of movement； and when one is
at rest the other is moved。 For example； in the line BAC； B is
moved； and A is the mover。 There must； however； be a point at rest
if one is to move； the other to be moved。 A （AE） then being one in
potency must be two in action； and so be a definite spatial
magnitude not a mathematical point。 Again； C may be moved
simultaneously with B。 Both the originals then in A must move and
be； and so there must be something other than them which moves but
is not moved。 For otherwise； when the movement begins； the extremes；
i。e。 the originals； in A would rest upon one another； like two men
putting themselves back to back and so moving their legs。 There must
then be some one thing which moves both。 This something is the soul；
distinct from the spatial magnitude just described and yet located
therein。
10
Although from the point of view of the definition of movement… a
definition which gives the cause… desire is the middle term or
cause； and desire moves being moved； still in the material animated
body there must be some material which itself moves being moved。 Now
that which is moved； but whose nature is not to initiate movement；
is capable of being passive to an external force； while that which
initiates movement