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

I say:
The difference between these two cases is very clear to the
philosophers, for from the assumption of infinite bodies existing
simultaneously there follows an infinite totality and an actual infinite, and
this is impossible. But time has no position, and from the existence of an
infinite temporal series of bodies no actual infinite follows.
Ghazali says on behalf of the philosophers:
I say:
The philosophers might say: The strict proof of the
impossibility of an infinite causal series is as follows: each
single cause of a series is either possible in itself or
necessary; if it is necessary, it needs no cause, and if it is
possible, then the whole series needs a cause additional to
its essence, a cause standing outside the series.
The first man to bring into philosophy the proof which Ghazali gives
here as a philosophical one, was Avicenna, who regarded this proof as
superior to those given by the ancients, since he claimed it to be based on
the essence of the existent, whereas the older proofs are based on
accidents consequent on the First Principle! This proof Avicenna took from
the theologians, who regarded the dichotomy of existence into possible
and necessary as self-evident, and assumed that the possible needs an
agent and that the world in its totality, as being possible, needs an agent
of a necessary existence. This was a theory of the Mu'tazilites before the
Ash'arites,s and it is excellent, and the only flaw in it is their assumption
that the world in its totality is possible, for this is not self-evident. Avicenna
wanted to give a general sense to this statement, and he gave to the
`possible' the meaning of `what has a cause',' as Ghazali relates. And
even if this designation can be conceded, it does not effect the division
which he had in view. For a primary division of existence into what has a
cause and what has no cause is by no means self-evident. Further, what
has a cause can be divided into what is possible and what is necessary. If
we understand by `possible' the truly possible we arrive at the necessarypossibles
and not at the necessary which has no cause; and if we
understand by `possible' that which has a cause and is also necessary,
there only follows from this that what has a cause has a cause and we
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