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

later the reprehensible consequences and absurdities which arise from the
doctrine that the First Principle possesses attributes additional to His
essence.
The fourth kind of plurality is that which occurs to a thing because of its
genus and specific difference; this plurality comes very near to that which
belongs to a thing because of its matter and form, for there are only
definitions for that which is composed of matter and form, and not for
simple, non-compound things, and nobody need disagree about denying a
plurality through definition to the First Principle.
The fifth kind of plurality is the plurality of essence and existence.
Existence in the nature of things is a logical concept which affirms the
conformity of a thing outside the soul with what is inside the soul. Its
meaning is synonymous with the true, and it is this that is meant by the
copula in categorical propositions. The term ‘existence’ is used in two
senses; the first synonymous with the true, when we ask, for instance, if
something exists or not, or whether a certain thing has such and such a
quality or not. The second sense stands in relation to the existing things
as their genus, in the way the existent is divided into the ten categories,
and into substance and accident. When by existent is understood the true,
there is no plurality outside the souks when by existent is understood what
is understood by entity and thing, the term ‘existent’ is attributed
essentially to God and analogically to all other things in the way warmth is
attributed to fire and to all warm things? This is the theory of the
philosophers.
But Ghazali based his discussion on the doctrine of Avicenna, and this
is a false doctrine, for Avicenna believed that existence is something
additional to the essence outside the soul and is like an accident of the
essence. And if existence were a condition for the being of the essence
and a condition for the essence of the necessary existent, the necessary
existent would be composed of the conditioning and the conditioned and it
would be of a possible existence. Avicenna affirms also that what exists as
an addition to its essence has a cause. Now, existence for Avicenna is an
accident which supervenes on the essence, and to this Ghazali refers
when he says:
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