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

impossible that such a thing should be known by proof, if
there is a proof and this proof is valid, but we must say that
what they have given as a proof has only the value of a
conjecture, but lacks all strictness.
Their device is that they say that heaven is moved, and
this is a premiss given by perception. And every body moved
has a mover, which is a premiss established by reason,
since if body were moved merely by being body, every body
would be in motion. ‘ Every mover receives its impulse either
from the moved itself, like the nature in the stone which falls
and the will in the movement of the animal conjoined with its
power to move, or from an external mover which moves
through constraint, as when a stone is flung upwards.
Everything that is moved by something existing in itself is
either unconscious of its movement (and we call this nature),
like the falling of the stone, or conscious (and we call this
voluntary or animated). This disjunction, that a movement is
either constrained or natural or voluntary, comprises all the
cases completely, so that if a movement does not fall under
two of these divisions it must be of the third type. Now the
movement of heaven cannot be constrained, because the
mover of a movement by constraint is either (i) another body
which is moved by constraint or by will, and in this case we
must finally no doubt arrive at a will as mover, and when in
the heavenly bodies a body moved through will is
established, then our aim is reached, for what use is it to
assume movements through constraint when finally we must
admit a will? or (2) God is the mover of its movement by
constraint without intermediary, and this is impossible; for if it
moves through Him in so far as it is a body and in so far as
He is its creator, then necessarily every body ought to be
moved. ;
This movement, therefore, must be distinguished by a
quality which marks this body off from all other bodies; and
this quality will be its proximate mover, either by will or by
nature. And it cannot be said that God moves it through His
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