by Aristotle
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 must needs possess a kind of force and power. Now
experience shows us that animals do both possess connatural spirit and
derive power from this. (How this connatural spirit is maintained in
the body is explained in other passages of our works.) And this spirit
appears to stand to the soul-centre or original in a relation
analogous to that between the point in a joint which moves being moved
and the unmoved. Now since this centre is for some animals in the
heart, in the rest in a part analogous with the heart, we further
see the reason for the connatural spirit being situate where it
actually is found. The question whether the spirit remains always
the same or constantly changes and is renewed, like the cognate
question about the rest of the parts of the body, is better postponed.
At all events we see that it is well disposed to excite movement and
to exert power; and the functions of movement are thrusting and
pulling. Accordingly, the organ of movement must be
capable of
expanding and contracting; and this is precisely the characteristic of
spirit. It contracts and expands naturally, and so is able to pull and
to thrust from one and the same cause, exhibiting gravity compared
with the fiery element, and levity by comparison with the opposites of
fire. Now that which is to initiate movement without change of
structure must be of the kind described, for the elementary bodies
prevail over one another in a compound body by dint of
disproportion; the light is overcome and kept down by the heavier, and
the heavy kept up by the lighter.
We have now explained what the part is which is moved when the
soul originates movement in the body, and what is the reason for this.
And the animal organism must be conceived after the similitude of a
well-governed commonwealth. When order is once established in it there
is no more need of a separate monarch to preside over each several
task. The individuals each play their assigned part as it is
ordered, and one thing follows another in its accustomed order. So
in animals there is the same orderliness- nature taking the place of
custom- and each part naturally doing his own work as nature has
composed them. There is no need then of a soul in each part, but she
resides in a kind of central governing place of the body, and the
remaining parts live by continuity of natural structure, and play
the parts Nature would have them play.
11
So much then for the voluntary movements of animal bodies, and the
reasons for them. These bodies, however, display in certain members
involuntary movements too, but most often non-voluntary movements.
By involuntary I mean motions of the heart and of the privy member;
for often upon an image arising and without express mandate of the
reason these parts are moved. By non-voluntary I mean sleep and waking
and respiration, and other similar organic movements. For neither
imagination nor desire is properly mistress of any of these; but since
the animal body must undergo natural changes of quality, and when
the parts are so altered some must increase and other decrease, the
body must straightway be moved and change with the changes that nature
makes dependent upon one another. Now the causes of the movements
are natural changes of temperature, both those coming from outside the
body, and those taking place within it. So the involuntary movements
which occur in spite of reason in the aforesaid parts occur when a
change of quality supervenes. For conception and imagination, as we
said above, produce the conditions necessary to affections, since they
bring to bear the images or forms which tend to create these states.
And the two parts aforesaid display this motion more conspicuously
than the rest, because each is in a sense a separate vital organism,
the reason being that each contains vital moisture. In the case of the
heart the cause is plain, for the heart is the seat of the senses,
while an indication that the generative organ too is vital is that
there flows from it the seminal potency, itself a kind of organism.
Again, it is a reasonable arrangement that the movements arise in
the centre upon movements in the parts, and in the parts upon
movements in the centre, and so reach one another. Conceive A to be
the centre or starting point. The movements then arrive at the
centre from each letter in the diagram we have drawn, and flow back
again from the centre which is moved and changes, (for the centre is
potentially multiple) the movement of B goes to B, that of C to C, the
movement of both to both; but from B to C the movements flow by dint
of going from B to A as to a centre, and then from A to C as from a
centre.
Moreover a movement contrary to reason sometimes does and
sometimes does not arise in the organs on the occasion of the same
thoughts; the reason is that sometimes the matter which is passive
to the impressions is there in sufficient quantity and of the right
quality and sometimes not.
And so we have finished our account of the reasons for the parts
of each kind of animal, of the soul, and furthere of sense-perception,
of sleep, of memory, and of movement in general; it remains to speak
of animal generation.
-THE END-
.
350 BC
ON THE PARTS OF ANIMALS
by Aristotle
translated by William Ogle
Book I
1
EVERY systematic science, the humblest and the noblest alike,
seems to admit of two distinct kinds of proficiency; one of which
may be properly called scientific knowledge of the subject, while
the other is a kind of educational acquaintance with it. For an
educated man should be able to form a fair off-hand judgement as to
the goodness or badness of the method used by a professor in his
exposition. To be educated is in fact to be able to do this; and
even the man of universal education we deem to be such in virtue of
his having this ability. It will, however, of course, be understood
that we only ascribe universal education to one who in his own
individual person is thus critical in all or nearly all branches of
knowledge, and not to one who has a like ability merely in some
special subject. For it is possible for a man to have this
competence in some one branch of knowledge without having it in all.
It is plain then that, as in other sciences, so in that which
inquires into nature, there must be certain canons, by reference to
which a hearer shall be able to criticize the method of a professed
exposition, quite independently of the question whether the statements
made be true or false. Ought we, for instance (to give an illustration
of what I mean), to begin by discussing each separate species-man,
lion, ox, and the like-taking each kind in hand inde. pendently of the
rest, or ought we rather to deal first with the attributes which
they have in common in virtue of some common element of their
nature, and proceed from this as a basis for the consideration of them
separately? For genera that are quite distinct yet oftentimes
present many identical phenomena, sleep, for instance, respiration,
growth, decay, death, and other similar affections and conditions,
which may be passed over for the present, as we are not yet prepared
to treat of them with clearness and precision. Now it is plain that if
we deal with each species independently of the rest, we shall
frequently be obliged to repeat the same statements over and over
again; for horse and dog and man present, each and all, every one of
the phenomena just enumerated. A discussion therefore of the
attributes of each such species separately would necessarily involve
frequent repetitions as to characters, themselves identical but
recurring in animals specifically distinct. (Very possibly also
there may be other characters which, though they present specific
differences, yet come under one and the same category. For instance,
flying, swimming, walking, creeping, are plainly sp
ecifically
distinct, but yet are all forms of animal progression.) We must, then,
have some clear understanding as to the manner in which our
investigation is to be conducted; whether, I mean, we are first to
deal with the common or generic characters, and afterwards to take
into consideration special peculiarities; or whether we are to start
straight off with the ultimate species. For as yet no definite rule
has been laid down in this matter. So also there is a like uncertainty
as to another point now to be mentioned. Ought the writer who deals
with the works of nature to follow the plan adopted by the
mathematicians in their astronomical demonstrations, and after
considering the phenomena presented by animals, and their several
parts, proceed subsequently to treat of the causes and the reason why;
or ought he to follow some other method? And when these questions
are answered, there yet remains another. The causes concerned in the
generation of the works of nature are, as we see, more than one. There
is the final cause and there is the motor cause. Now we must decide
which of these two causes comes first, which second. Plainly, however,
that cause is the first which we call the final one. For this is the
Reason, and the Reason forms the starting-point, alike in the works of
art and in works of nature. For consider how the physician or how
the builder sets about his work. He starts by forming for himself a
definite picture, in the one case perceptible to mind, in the other to
sense, of his end-the physician of health, the builder of a
house-and this he holds forward as the reason and explanation of
each subsequent step that he takes, and of his acting in this or
that way as the case may be. Now in the works of nature the good end
and the final cause is still more dominant than in works of art such
as these, nor is necessity a factor with the same significance in them
all; though almost all writers, while they try to refer their origin
to this cause, do so without distinguishing the various senses in
which the term necessity is used. For there is absolute necessity,