Those people, however, say that existence is something additional to essence, that essences are not brought into being, and that the existence of every thing is additional to its essence. Some adherents of philosophy draw distinctions concerning existence, the necessary, and the contingent, saying:
“Necessary existence is identical with essence, whereas contingent existence is additional to essence.”
Their specious argument is the one mentioned earlier: a person may know a thing’s essence without knowing its existence, and existence is common to existing things, whereas each thing’s essence is peculiar to it. Whoever reflects will discern the truth of the matter, for we have explained the distinction between existence in knowledge and actual existence.
This distinction applies to existence, the thing itself, subsistence, essence, and other such matters. Their subsistence in knowledge, writing, and speech is not their subsistence in external reality, which is the subsistence of their very reality and essence. When a person conceives an essence, he knows its mental existence, but this does not entail its real, external existence.
Thus, when someone says, “I have conceived the thing’s reality, its very being, its self, and its essence, but I do not know its existence,” or, “Its existence in knowledge has been attained, but not its actual, real existence,” its real essence, its real being, and its real self in external reality remain unknown. There is therefore no difference between the expression “its existence” and the expression “its essence,” except that one expression may refer to what is in the mind and the other to what is in external reality. The distinction thus arises from where they subsist, not from essence and existence themselves.
As for their assertion that existence is shared, whereas reality is not, the same answer applies. The particular existence found in external reality is not shared, just as the particular reality found in external reality is not shared. Rather, knowledge apprehends the common existent