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

I say:
of theirs which we have mentioned, which is based on the
denial of plurality in the First; we have shown its futility, and
apart from it there is no other method. It is therefore clear
that for the man who does not believe in the temporal
creation of bodies there is no foundation for believing in a
creator at all.
This argument is, without doubt, binding for the man who follows the
method of a necessary existent to prove the existence of an incorporeal
being, but this is not the method followed by the ancient philosophers, and
the first, so far as we know, who used it was Avicenna. He said that it was
superior to the proof of the ancients, because the ancients arrived only at
an immaterial being, the principle of the universe, through derivative
things, namely motion and time; whereas this proof, according to
Avicenna, arrives at the assertion of such a principle as the ancients
established, through the investigation of the nature of the existent in so far
as it is an existent. If indeed it did arrive at such an affirmation, what
Avicenna says would be true; however, it does not. ‘ For the most that
could be affirmed of the existent necessarily existing by itself would be
that it is not composed of matter and form, and generally speaking that it
has no definition. But if it is supposed to exist as composed of eternal
parts which are continuous by nature, as is the case with the world and its
parts, it may indeed be said of the world with its parts that it is a necessary
existent, z it being of course understood that there is a necessary existent.
And we have already said that the method Avicenna followed to establish
an existent of this description is not demonstrative and does not by nature
lead to it, except in the way we have stated. The utmost consequence of
this argument-and this constitutes its weakness-is the theory of those,
namely the Peripatetics, who assume that there exists a simple body not
composed of matter and form. For the man who assumes an eternal
compound of actual parts must necessarily acknowledge that it is
essentially one, and every oneness in a compound is one through an
essential unity, namely a simple, and through this unity the world becomes
one, and therefore Alexander of Aphrodisias says that there must exist a
spiritual force which is diffused in all the parts of the universe in the same
way as there is a force in all the parts of a single animal which binds them
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