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

principle which is the cause of that which exists in all the other things of
this genus, just as our term ‘warm’ is a term which is predicated per prius
et posterius of fire and all other warm things, and that of which it is
asserted first, i. e. fire, is the cause of the existence of warmth in all other
things, and the same is the case with substance, intellect, and principle
and such terms (most metaphysical terms are of this kind), and such
terms can indicate both substances and accidents.
And what he says of the description of substance is devoid of sense,
but existence is the genus of substance and is included in its definition in
the way the genera of the sublunary things are included in their definitions,
and Farabi proved this in his book about demonstration, and this is the
commonest view amongst philosophers. Avicenna erred in this only
because, since he thought that the ‘existent’ means the ‘true’ in the Arabic
language, and that what indicates the true indicates an accident4-the true,
however, really indicates one of the second, predicates, i. e. a predicablehe
believed that when the translator used the word ‘existent’ it meant only
the ‘true’. This, however, is not so, for the translators meant only to
indicate what is also meant by ‘entity’ and ‘thing’. Farabi explains this in
his Book of the Letters and he shows that one of the reasons for the
occurrence of this mistake is that the term ‘existent’ in Arabic is a
derivative in form and that a derivative signifies an accident, and in fact an
accident is linguistically a derivative. But since the translators did not find
in Arabic a term which signified that concept which the ancient
philosophers subdivided into substance and accident, potency and act, a
term namely which should be a primitive symbol, some translators
signified that concept by the term ‘existent’, not to be understood as
having a derivative meaning and signifying therefore an accident, but as
having the same meaning as ‘essence’. It is thus a technical term, not an
idiomatic word. Some translators, because of the difficulty attached to it,
decided to use for the concept, which the Greek language tried to express
by deriving it from the pronoun which joins the predicate and the subject,
the term which expresses this, because they thought that this word comes
nearer to expressing this meaning, and they used instead of the term
‘existent’ the term ‘haeceitas’, but the fact that its grammatical form is not
found in Arabic hindered its use, and the other party therefore preferred
the term ‘existent’. -, And the term ‘existent’ which signifies the true does
not signify the quiddity, and therefore one may often know the quiddity
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