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

the real possible-that should be understood, but merely that its essence
determines that its existence can become necessary only through a
cause; what is meant, therefore, is an essence which will not be by itself
necessary in its existence when its cause is removed and therefore is not
a necessary existent, i.e. it is denied the quality of necessary existence. It
is as if Ghazali said that the necessary existent is partially necessary
through itself, partially through a cause, and that which is necessary
through a cause is not necessary through itselfb Nobody doubts that these
specific differences are neither substantial differences which divide the
essence nor additions to the essence, but that they are only negative or
relative relations, just as, when we say that a thing exists, the word ‘exists’
does not indicate an entity added to its essence outside the soul, which is
the case when we say of a thing that it is white. It is here that Avicenna
erred, for he believed that unity is an addition to the essence and also that
existence, when we say that a thing exists, is an addition to the things This
question will be treated later. And the first to develop this theory of the
existent, possible by itself and necessary through another, was Avicenna;
for him possibility was a quality in a thing, different from the thing in which
the possibility is, and from this it seems to follow that what is under the
First is composed of two things, one to which possibility is attributed, the
other to which necessity is attributed; but this is a mistaken theory. But he
who has understood our explanation will not be concerned about the
difficulty which Ghazali adduces against Avicenna. The only question he
will have to ask, when he has understood the meaning of ‘possibility of
existence’ for the first effect, is whether this possibility brings about a
compound character in the first effect or not, for if the quality is relative, it
does not bring about a compound character. For not all the different
dispositions which can be imagined in a thing need determine additional
qualities in its essence outside the soul; indeed, this is the case with the
disposition of privations and relations, and for this reason certain
philosophers do not count the category of relation among things which
exist outside the soul, i.e. the ten categories. Ghazali, however, implies in
his argument that any additional meaning must apply to an additional
entity actually outside the soul; but this is a mistake, and a sophistical
argument. This follows from his words
Generally speaking, existence is a universal which can be divided into
necessary and possible, and if the one specific difference is an addition to
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