第 1 节
作者:一意孤行      更新:2021-02-27 00:36      字数:9322
  ON THE MOTION OF ANIMALS
  by Aristotle
  translated by A。 S。 L。 Farquharson
  1
  ELSEWHERE we have investigated in detail the movement of animals
  after their various kinds; the differences between them; and the
  reasons for their particular characters (for some animals fly; some
  swim; some walk; others move in various other ways); there remains
  an investigation of the common ground of any sort of animal movement
  whatsoever。
  Now we have already determined (when we were discussing whether
  eternal motion exists or not; and its definition; if it does exist)
  that the origin of all other motions is that which moves itself; and
  that the origin of this is the immovable; and that the prime mover
  must of necessity be immovable。 And we must grasp this not only
  generally in theory; but also by reference to individuals in the world
  of sense; for with these in view we seek general theories; and with
  these we believe that general theories ought to harmonize。 Now in
  the world of sense too it is plainly impossible for movement to be
  initiated if there is nothing at rest; and before all else in our
  present subject… animal life。 For if one of the parts of an animal
  be moved; another must be at rest; and this is the purpose of their
  joints; animals use joints like a centre; and the whole member; in
  which the joint is; becomes both one and two; both straight and
  bent; changing potentially and actually by reason of the joint。 And
  when it is bending and being moved one of the points in the joint is
  moved and one is at rest; just as if the points A and D of a
  diameter were at rest; and B were moved; and DAC were generated。
  However; in the geometrical illustration; the centre is held to be
  altogether indivisible (for in mathematics motion is a fiction; as the
  phrase goes; no mathematical entity being really moved); whereas in
  the case of joints the centres become now one potentially and
  divided actually; and now one actually and divided potentially。 But
  still the origin of movement; qua origin; always remains at rest
  when the lower part of a limb is moved; for example; the elbow
  joint; when the forearm is moved; and the shoulder; when the whole
  arm; the knee when the tibia is moved; and the hip when the whole leg。
  Accordingly it is plain that each animal as a whole must have within
  itself a point at rest; whence will be the origin of that which is
  moved; and supporting itself upon which it will be moved both as a
  complete whole and in its members。
  2
  But the point of rest in the animal is still quite ineffectual
  unless there be something without which is absolutely at rest and
  immovable。 Now it is worth while to pause and consider what has been
  said; for it involves a speculation which extends beyond animals
  even to the motion and march of the universe。 For just as there must
  be something immovable within the animal; if it is to be moved; so
  even more must there be without it something immovable; by
  supporting itself upon which that which is moved moves。 For were
  that something always to give way (as it does for mice walking in
  grain or persons walking in sand) advance would be impossible; and
  neither would there be any walking unless the ground were to remain
  still; nor any flying or swimming were not the air and the sea to
  resist。 And this which resists must needs be different from what is
  moved; the whole of it from the whole of that; and what is thus
  immovable must be no part of what is moved; otherwise there will be no
  movement。 Evidence of this lies in the problem why it is that a man
  easily moves a boat from outside; if he push with a pole; putting it
  against the mast or some other part; but if he tried to do this when
  in the boat itself he would never move it; no not giant Tityus himself
  nor Boreas blowing from inside the ship; if he really were blowing
  in the way painters represent him; for they paint him sending the
  breath out from the boat。 For whether one blew gently or so stoutly as
  to make a very great wind; and whether what were thrown or pushed were
  wind or something else; it is necessary in the first place to be
  supported upon one of one's own members which is at rest and so to
  push; and in the second place for this member; either itself; or
  that of which it is a part; to remain at rest; fixing itself against
  something external to itself。 Now the man who is himself in the
  boat; if he pushes; fixing himself against the boat; very naturally
  does not move the boat; because what he pushes against should properly
  remain at rest。 Now what he is trying to move; and what he is fixing
  himself against is in his case the same。 If; however; he pushes or
  pulls from outside he does move it; for the ground is no part of the
  boat。
  3
  Here we may ask the difficult question whether if something moves
  the whole heavens this mover must be immovable; and moreover be no
  part of the heavens; nor in the heavens。 For either it is moved itself
  and moves the heavens; in which case it must touch something immovable
  in order to create movement; and then this is no part of that which
  creates movement; or if the mover is from the first immovable it
  will equally be no part of that which is moved。 In this point at least
  they argue correctly who say that as the Sphere is carried round in
  a circle no single part remains still; for then either the whole would
  necessarily stand still or its continuity be torn asunder; but they
  argue less well in supposing that the poles have a certain force;
  though conceived as having no magnitude; but as merely termini or
  points。 For besides the fact that no such things have any
  substantial existence it is impossible for a single movement to be
  initiated by what is twofold; and yet they make the poles two。 From
  a review of these difficulties we may conclude that there is something
  so related to the whole of Nature; as the earth is to animals and
  things moved by them。
  And the mythologists with their fable of Atlas setting his feet upon
  the earth appear to have based the fable upon intelligent grounds。
  They make Atlas a kind of diameter twirling the heavens about the
  poles。 Now as the earth remains still this would be reasonable enough;
  but their theory involves them in the position that the earth is no
  part of the universe。 And further the force of that which initiates
  movement must be made equal to the force of that which remains at
  rest。 For there is a definite quantity of force or power by dint of
  which that which remains at rest does so; just as there is of force by
  dint of which that which initiates movement does so; and as there is a
  necessary proportion between opposite motions; so there is between
  absences of motion。 Now equal forces are unaffected by one another;
  but are overcome by a superiority of force。 And so in their theory
  Atlas; or whatever similar power initiates movement from within;
  must exert no more force than will exactly balance the stability of
  the earth… otherwise the earth will be moved out of her place in the
  centre of things。 For as the pusher pushes so is the pushed pushed;
  and with equal force。 But the prime mover moves that which is to begin
  with at rest; so that the power it exerts is greater; rather than
  equal and like to the power which produces absence of motion in that
  which is moved。 And similarly also the power of what is moved and so
  moves must be greater than the power of that which is moved but does
  not initiate movement。 Therefore the force of the earth in its
  immobility will have to be as great as the force of the whole heavens;
  and of that which moves the heavens。 But if that is impossible; it
  follows that the heavens cannot possibly be moved by any force of this
  kind inside them。
  4
  There is a further difficulty about the motions of the parts of
  the heavens which; as akin to what has gone before; may be
  considered next。 For if one could overcome by force of motion the
  immobility of the earth he would clearly move it away from the centre。
  And it is plain that the power from which this force would originate
  will not be infinite; for the earth is not infinite and therefore
  its weight is not。 Now there are more senses than one of the word
  'impossible'。 When we say it is impossible to see a sound; and when we
  say it is impossible to see the men in the moon; we use two senses
  of the word; the former is of necessity; the latter; though their
  nature is to be seen; cannot as a fact be seen by us。 Now we suppose
  that