Thomas Aquinas

“ And as in the objects of the senses, whence the intellect derives its knowledge, the nature of the species is made individual by the matter, and thus the nature is as the form, and the individual is the "suppositum" of the form; so also in God the essence is taken as the form of the three persons, according to our mode of signification. Now in creatures we say that every form belongs to that whereof it is the form; as the health and beauty of a man belongs to the man. ”

“ But the "use" by which we enjoy God, is likened to the property of the Holy Ghost as the Gift; and Augustine points to this when he says (De Trin. vi, 10) : "In the Trinity, the Holy Ghost, the sweetness of the Begettor and the Begotten, pours out upon us mere creatures His immense bounty and wealth." Thus it is clear how "eternity," "species," and "use" are attributed or appropriated to the persons, but not essence or operation; because, being common, there is nothing in their concept to liken them to the properties of the Persons. ”

“ For truth can be considered as existing in the thought or in the thing itself. Hence, as intellect and thing in their essential meaning, are referred to the essence, and not to the persons, so the same is to be said of truth. The definition quoted from Augustine belongs to truth as appropriated to the Son. ”

“ For nothing can be its own matter, nor its own active principle. Yet a thing may be its own form, as appears in all immaterial things. So, when we say, "three persons of one essence," taking essence as having the habitude of form, we do not mean that essence is different from person, which we should mean if we said, "three persons from the same essence." ”

“ As essence and person in God differ in our way of thinking, it follows that something can be denied of the one and affirmed of the other; and therefore, when we suppose the one, we need not suppose the other. ”

“ The word "essence," however, in its mode of signification, cannot stand for Person, because it signifies the essence as an abstract form. Consequently, what properly belongs to the persons whereby they are distinguished from each other, cannot be attributed to the essence. ”

“ So far as Godhead is one in several "supposita," it agrees in a certain degree with the form of a collective term. So when we say, "the Father is the principle of the whole Godhead," the term Godhead can be taken for all the persons together, inasmuch as it is the principle in all the divine persons. Nor does it follow that He is His own principle; as one of the people may be called the ruler of the people without being ruler of himself. We may also say that He is the principle of the whole Godhead ”

“ For the Father is not the Trinity; nor is the Son; nor is the Holy Ghost. So to say, "God is the Trinity," is false.
Objection 2: Further, the lower is not predicated of the higher except by accidental predication; as when I say, "animal is man"; for it is accidental to animal to be man. But this name "God" as regards the three persons is as a general term to inferior terms, as Damascene says (De Fide Orth. iii, 4) . Therefore it seems that the names of the persons cannot be predicated of this name "God," except in an accidental sense. ”

“ It would seem that the persons cannot be predicated of the concrete essential names; so that we can say for instance, "God is three persons"; or "God is the Trinity." For it is false to say, "man is every man," because it cannot be verified as regards any particular subject. For neither Socrates, nor Plato, nor anyone else is every man. ”

“ The preposition "from" or "out of" does not designate the habitude of a formal cause, but rather the habitude of an efficient or material cause; which causes are in all cases distinguished from those things of which they are the causes. ”

“ In an earthly son this is sometimes absent by reason of lack of years. "Goodness," as the nature and object of love, has likeness to the Holy Ghost; but seems repugnant to the earthly spirit, which often implies a certain violent impulse, according to Is. 25:4: "The spirit of the strong is as a blast beating on the wall." "Strength" is appropriated to the Son and to the Holy Ghost, not as denoting the power itself of a thing, but as sometimes used to express that which proceeds from power; for instance, we say that the strong work done by an agent is its strength. ”

“ The difference between substantive and adjectival names consist in this, that the former carry their subject with them, whereas the latter do not, but add the thing signified to the substantive. Whence logicians are wont to say that the substantive is considered in the light of "suppositum," whereas the adjective indicates something added to the "suppositum." Therefore substantive personal terms can be predicated of the essence, because they are really the same; nor does it follow that a personal property makes a distinct essence ”

“ In like manner, as in God the persons are multiplied, and the essence is not multiplied, we speak of one essence of the three persons, and three persons of the one essence, provided that these genitives be understood as designating the form. ”