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

the philosophers call substratum and matter. ? And they found that the
accidents also are divided in the intellect in a way similar to those two
natures, s although their substratum in which they exist in reality is the
bodies compounded of these two natures. And when they had
distinguished the intelligibles from the sensibles and it had become clear
to them that in sensible things there are two natures, potency and act,
they inquired which of these two natures was prior to the other and found
that the act was prior to the potency, because the agent was prior to its
object, ‘ and they investigated also causes and effects, which led them to
a primary cause which by its act is the first cause of all causes, and it
followed that this cause is pure act and that in it there is no potency at all,
since if there were potency in it, it would be in part an effect, in part a
cause, and could not be a primary cause. And since in everything
composed of attribute and subject there is potency and act, it was a
necessary implication for them that the First could not be composed of
attribute and subject, and since everything free from matter was according
to them intellect, it was necessary for them that the First should be
intellect.
This in summary is the method of the philosophers, and if you are one
of those whose mind is sufficiently trained to receive the sciences, and
you are steadfast and have leisure, it is your duty to look into the books
and the sciences of the philosophers, so that you may discover in their
works certain truths (or perhaps the reverse) ; but if you lack one of these
three qualities, it is your duty to keep yourself to the words of the Divine
Law, and you should not look for these new conceptions in Islam; for if you
do so, you will be neither a rationalist nor a traditionalist. ‘
Such was the philosophers’ reason for their belief that the essence
which they found to be the principle of the world was simple and that it
was knowledge and intellect. And finding that the order which reigns in the
world and its parts proceeds from a knowledge prior to it, they judged that
this intellect and this knowledge was the principle of the world, which gave
the world existence and made it intelligible. This is a theory very remote
from the primitive ideas of mankind and from common notions, so that it is
not permitted to divulge it to the masses or even to many people; indeed,
the man who has proved its evidence is forbidden to reveal it to the man
who has no power to discover its truth, for he would be like his murderer.
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