On The Parts Of Animals   

of a dead body, such I mean as its eye or its hand, is really an eye
or a hand. To say, then, that shape and colour constitute the animal
is an inadequate statement, and is much the same as if a woodcarver
were to insist that the hand he had cut out was really a hand. Yet the
physiologists, when they give an account of the development and causes
of the animal form, speak very much like such a craftsman. What,
however, I would ask, are the forces by which the hand or the body was
fashioned into its shape? The woodcarver will perhaps say, by the axe
or the auger; the physiologist, by air and by earth. Of these two
answers the artificer's is the better, but it is nevertheless
insufficient. For it is not enough for him to say that by the stroke
of his tool this part was formed into a concavity, that into a flat
surface; but he must state the reasons why he struck his blow in such
a way as to effect this, and what his final object was; namely, that
the piece of wood should develop eventually into this or that shape.
It is plain, then, that the teaching of the old physiologists is
inadequate, and that the true method is to state what the definitive
characters are that distinguish the animal as a whole; to explain what
it is both in substance and in form, and to deal after the same
fashion with its several organs; in fact, to proceed in exactly the
same way as we should do, were we giving a complete description of a
couch.
If now this something that constitutes the form of the living being be
the soul, or part of the soul, or something that without the soul
cannot exist; as would seem to be the case, seeing at any rate that
when the soul departs, what is left is no longer a living animal, and
that none of the parts remain what they were before, excepting in mere
configuration, like the animals that in the fable are turned into
stone; if, I say, this be so, then it will come within the province of
the natural philosopher to inform himself concerning the soul, and to
treat of it, either in its entirety, or, at any rate, of that part of
it which constitutes the essential character of an animal; and it will
be his duty to say what this soul or this part of a soul is; and to
discuss the attributes that attach to this essential character,
especially as nature is spoken of in two senses, and the nature of a
thing is either its matter or its essence; nature as essence including
both the motor cause and the final cause. Now it is in the latter of
these two senses that either the whole soul or some part of it
constitutes the nature of an animal; and inasmuch as it is the
presence of the soul that enables matter to constitute the animal
nature, much more than it is the presence of matter which so enables
the soul, the inquirer into nature is bound on every ground to treat
of the soul rather than of the matter. For though the wood of which
they are made constitutes the couch and the tripod, it only does so
because it is capable of receiving such and such a form.
What has been said suggests the question, whether it is the whole soul
or only some part of it, the consideration of which comes within the
province of natural science. Now if it be of the whole soul that this
should treat, then there is no place for any other philosophy beside
it. For as it belongs in all cases to one and the same science to deal
with correlated subjects-one and the same science, for instance, deals
with sensation and with the objects of sense-and as therefore the
intelligent soul and the objects of intellect, being correlated, must
belong to one and the same science, it follows that natural science
will have to include the whole universe in its province. But perhaps
it is not the whole soul, nor all its parts collectively, that
constitutes the source of motion; but there may be one part, identical
with that in plants, which is the source of growth, another, namely
the sensory part, which is the source of change of quality, while
still another, and this not the intellectual part, is the source of
locomotion. I say not the intellectual part; for other animals than
man have the power of locomotion, but in none but him is there
intellect. Thus then it is plain that it is not of the whole soul that
we have to treat. For it is not the whole soul that constitutes the