Having treated these matters, we can see clearly how essence is found in various kinds of things. There are three ways in which substances may have an essence. First, surely, is the way God has his essence, which is his very existence itself, and so we find certain philosophers saying that God does not have a quiddity or essence because his essence is not other than his existence. From this it follows that he is not in a genus, for everything that is in a genus has a quiddity beyond its existence, since the quiddity or nature of the genus or species is not in the order of nature distinguished in the things of which it is the genus or species, but the existence is diverse in diverse things.
Even though we say that God is existence alone we do not fall into the error of those who said that God is that universal existence by which everything formally exists. The existence which is God is of such a kind that no addition can be made to it, whence through its purity it is distinct from every other existence; for this reason the author of the Liber de Causis , prop. 9, com., says that the individuation of the first cause, which is being alone, is through its pure goodness. But common existence, just as it does not include in its concept any addition, so too in its concept does it not exclude any addition; for, if such existence did in its concept exclude any addition, nothing could be understood to exist in which there was added something beyond existence.
Similarly, although God is existence alone, the remaining perfections and nobilities are not lacking in him. On the contrary, he has all the perfections that exist in every genus, and for this reason he is called perfect without qualification, as the Philosopher, V Metaphysicae cap. 16 (1021b30-33), and the Commentator, Metaphysicae V, com.
21, each say. But God has these perfections in a more excellent way than all other things have them because in him they are one, while in other things they are diverse. And this is because all these perfections pertain to God according to his simple existence, just as, if someone through one quality could effect the operations of all qualities, such a person would have in that one quality all the qualities, so too does God in his very existence have all the perfections.
In a second way, essence is found in created intellectual substances, in which existence is other than essence, although in these substances the essence is without matter. Hence, their existence is not absolute but received, and so finite and limited by the capacity of the receiving nature;but their nature or quiddity is absolute and is not received in any matter.
Thus, the author of the Liber de Causis , prop. 16, com., says that intelligences are infinite in an inferior way and finite in a superior way: they are finite with respect to their existence, which they receive from something superior, though they are not rendered finite in an inferior way because their forms are not limited to the capacity of some matter receiving them. And thus among such substances we do not find a multitude of individuals in one species, as said above, except in the case of the human soul, and there we do find a multitude of individuals in one species because of the body to which the soul is united. Now, the individuation of the soul depends on the body, in an occasional manner, as to its inception, for the soul does not acquire for itself individual existence unless in the body of which it is the act. But nevertheless, if we subtract the body, the individuation does not perish because, since the soul was made the form of a given body, the form has absolute existence from which it has acquired individuated existence, and this existence always remains individuated.
And thus Avicenna says, De Anima V, cap. 3, that the individuation of souls and their multiplication depend on the body for their beginning but not for their end.
