On The Motion Of Animals   

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;