Aristotle

by Various Works [lit]

  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,