Summa summae S. Thomae sive compendium theologiae

I presuppose, as something commonly accepted against a few authors, that the divine essence, considered prior in conception to the relations, exists through its own proper and absolute existence; because, considered prior to the relations, it is pure act, therefore actually existing; it is an uncreated being, therefore existing of itself; it acts by understanding and willing, therefore it exists. Finally, existence itself is included in the very notion of divinity; for it is a being existing of itself, according to the text of Exodus III, 14: I am who am.

I answer: The divine relations or persons do not possess their own relative existences, but exist through one absolute existence of the essence.¹

The first proof. Absolute realities are not multiplied in God, because they are not relatively opposed to one another; and all things are one in God where relative opposition does not intervene, as has already been said. Hence, although there are three persons, there are not three acts of understanding, three acts of willing, or three powers. But the existence of a relation or person, which is improperly called relative, is something absolute. Therefore. The minor is proved. 1º The existence of a relation does not consist in an order toward a term, but in an order toward the subject in which it inheres. For the existence of a relation in creatures is nothing other than inherence (inesse), while in God it is subsistent being (esse per se). Therefore it is something absolute and not relative. 2º Existence belongs to a relation not according to the concept toward (ad), but according to the concept in (in): first, because the concept ad abstracts from existence, as will be said in the following article; secondly, because that which confers existence must exercise some causality with respect to it, whereas a mere term only terminates and does not actively cause anything. Therefore.

The second proof. The divine relations or persons exist through the absolute existence of the essence. Therefore relative existences are superfluous and indeed imply a contradiction. The antecedent and the consequence must be proved. The antecedent is proved. In God, existence is essentially identical with essence; for He is a being existing through itself. The essence is communicated to the relations or persons, and consequently so is its existence. But existence cannot be communicated to anything unless it renders that thing existent, just as wisdom or whiteness cannot be communicated to a man unless they render him wise or white. For the formal effect of a form is the form itself as communicated. Therefore the divine relations or persons exist through the absolute existence of the essence. The consequence as to its first part is proved. What already exists does not require another existence; for by the first existence it is already outside nothingness and outside all causes. Therefore relative existences are superfluous. The same consequence as to its second part is proved. 1º It implies a contradiction that what is already outside nothingness and outside all causes (which is the formal effect of existence) should again be placed outside nothingness and outside all causes. 2º It implies the existence of two ultimate actualities, or two ultimate termini of the same order and kind, because then neither would be ultimate. But existence is the ultimate actuality and the ultimate terminus of a thing. Therefore.