Existence vs Being
By Hector Delbosco - Saint Thomas would never say "God exists"
Professor Hector Delbosco 1 explains the controversy regarding the use of word “existence” in opposition of word “being” in the works of Saint Thomas Aquinas. The explanation can be found in spanish on the YouTube Channel iAquinas. There is an excellent transcription to English which I copy to here.
The relationship between act of being and essence is an act-potency relationship, the "esse" — the act of being — is an act of the essence. Therefore, the essence, without the act of being, is a mere possibility. It is pure potentiality. It is true that philosophical knowledge seeks the essence of things, and that, therefore, the essence as such is important, but when, in a metaphysical sense, priority is given to the essence, one ends up in what we might call an "essentialism" that reduces, that subordinates enormously the effective reality of things, which comes only from their act of being.
In Saint Thomas, the primacy of "esse," as an act, over essence is very clear, and that must always be kept in mind when one strives to go, philosophically speaking, deeper into these concepts.A second point would be the terminological precision of "being" [as the verb, "to be"] and "ens" or "being" [entity or noun].
In English — as in many modern languages — we use the word "being" in order to designate things that are: one being, many beings, and so on; but in reality, if we take language in its fundamental and precise sense, "to be" is an infinitive, and the infinitive is never used to designate the concrete subjects that perform that action. The infinitive is used to designate an action, or — as in this case — "being" [used as a verb] is more than an action. It is the first act of things. So it is that if we were to be strict with words, the word, "being" ["to be"] designates only the act. And how do we designate the subject? Normally we designate it with the [Latin] participle: "ens" ["entity"], in this case. Of the action of studying, the subject who performs it is the student, of sleeping it is the sleeper, and the one who realizes the act of being ("esse"), is the "ens" ["entity" or "being" as a noun].
For this reason, philosophically, it is always better to use the word "ens" or "entity" to designate things that are, and reserve the word "being" for the act by which they are. That is an important distinction.
And thirdly, the Thomistic school, for a certain time, used the expression "existence" to designate the act of being, and would speak, then, of this third composition as a composition of essence and existence. It is not actually the best formulation. There are two reasons why it is not the most appropriate thing to designate the act of being as "existence" — apart from the fact that Saint Thomas hardly ever uses that terminology — but there are two reasons why one does not use it: first, because the very word, "existence," is not an infinitive, so it does not designate the act as an act. Rather, it would designate an essence: the essence of existing — a thing like that — which then is not appropriate. But, secondly, because etymologically, in Latin, "to exist" comes from "ex-sistere," whose first meaning is "to come forth from.". There exists that which comes from elsewhere, that is, that which is caused, to the point where Saint Thomas would never say, "God exists," [but rather,] "God is.". Therefore, more perfect, more precise than using the terms, "essence-existence," is to use the expression, "essence-act of being," or in any case, "essence-esse," using the Latin infinitive.
Professor Hector Delbosco is Dean of Faculty of Philosophy of Universidad del Norte Santo Tomás de Aquino in Argentina