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

disappearance of knowledge. For knowledge and the objectknown
are two things, the former dependent on the latter,
and if we supposed rational beings to turn away from
possibility and neglect it, we should say: ‘It is not possibility
that is annulled, for the possibilities subsist by themselves,
but it is simply that minds neglect them or that minds and
rational beings have disappeared; but possibility remains,
without any doubt.’ And the three proofs are not valid, for
impossibility requires an existent to which it can be related,
and impossibility means identifying two opposites, and if the
substratum were white it could not become black as long as
the white existed, and therefore we need a substratum,
qualified by the quality during the inherence of which its
opposite is spoken of as impossible in this substratum, and
therefore impossibility is a relative attribute subsistent in a
substratum and related to it. And where the necessary is
concerned it is evident that it is related to necessary
existence.
As concerns the second proof, that black is in itself
possible, this is a mistake, for if it is taken, abstracted from
the substratum in which it inheres, it is impossible, not
possible; it only becomes possible when it can become a
form in a body; the body is then in readiness for the
interchange, and the interchange is possible for the body;
but in itself black has no individuality, so as to be
characterizable by possibility.
As concerns the third proof about the soul, it is eternal for
one school of philosophers, and is only possible in the
attaching of itself to bodies, and therefore against those
philosophers the argument does not apply= But for those
who admit that the soul comes into existence-and one
school of philosophers has believed that it is impressed on
matter and follows its temperament, as is indicated by Galen
in certain passages-it comes into existence in matter and its
possibility is related to its matter.’ And according to the
theory of those who admit that it comes into existence,
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