Tahafut_al-Tahafut-transl-Engl-van-den-Bergh

move itself in space, in a definite direction, not at random, through its own
power, not through an exterior cause, and move in opposite directions at
the same time, we are absolutely sure that it is a living being, and we said
only ‘not through an exterior cause’ because iron moves towards a
magnet when the magnet is brought to it from the outside-and besides,
iron moves to a magnet from any direction whatever., The heavenly
bodies, therefore, possess places which are poles by nature, and these
bodies cannot have their poles in other places, just as earthly animals
have particular organs in particular parts of their bodies for particular
actions, and cannot have them in other places, e.g. the organs of
locomotion, which are located in definite parts. The poles represent the
organs of locomotion in animals of spherical form, and the only difference
in this respect between spherical and non-spherical animals is that in the
latter these organs differ in both shape and power, whereas in the former
they only differ in power. For this reason it has been thought on first sight
that they do not differ at all, and that the poles could be in any two points
on the sphere. And just as it would be ridiculous to say that a certain
movement in a certain species of earthly animal could be in any part
whatever of its body, or in that part where it is in another species, because
this movement has been localized in each species in the place where it
conforms most to its nature, or in the only place where this animal can
perform the movement, so it stands with the differentiation in the heavenly
bodies for the place of their poles. For the heavenly bodies are not one
species and numerically many, but they form a plurality in species, like the
plurality of different individuals of animals where there is only one
individual in the species.
Exactly the same answer can be given to the question why the heavens
move in different directions: that, because they are animals, they must
move in definite directions, like right and left, before and behind, which are
directions determined by the movements of animals, and the only
difference between the movements of earthly animals and those of
heavenly bodies is that in the different animals these movements are
different in shape and in power, whereas in the heavenly animals they
only differ in power. And it is for this reason that Aristotle thinks that
heaven possesses the directions of right and left, before and behind, high
and low. The diversity of the heavenly bodies in the direction of their
movements rests on their diversity of species, and the fact that this
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