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

eternally. Therefore let the different types of His knowledge
proceed from Him in this way.
And as to the other alternative, that His knowledge
should proceed from another, we answer: Why is that
impossible according to you? There are here only three
difficulties. The first is the changing, but we have already
shown that this is a consequence of your theory.
The second difficulty, that one thing should be the cause
of a change in another, is not impossible according to you;
for let the occurrence of the thing be the cause of the
occurrence of its being known, just as you say that the
appearance of a coloureds figure in front of the pupil of the
eye is the cause of the impression of the image of this figure
on the vitreous humour of the pupil through the medium of
the transparent air between the pupil and the figure seen ;b
and if therefore an inanimate object can be the cause of the
impression of the form on the pupil-and this is the meaning
of sight-why should it be impossible that the occurrence of
temporal beings should cause the First to acquire its
knowledge of them? And just as the potency of seeing is
disposed to perceive, and the appearance of the coloured
figure, when the obstacles are removed, is the cause of the
actualization of the perception, so let according to you the
essence of the First Principle be disposed to receive
knowledge and emerge from potency into act through the
existence of this temporal being. And if this implies a change
in the eternal, a changing eternal is not impossible according
to you. And if you protest that this is impossible in the
necessary existent, you have no other proof for establishing
the necessary existent than the necessity of a termination to
the series of causes and effects, as has been shown
previously, and we have proved that to end this series with
an eternal being which can change is not impossible.
The third difficulty in the problem is that if the Eternal
could change through another, this would be like subjection
and the control of another over Him.
370