Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that essential names, as the name "God," should not be predicated in the singular of the three persons, but in the plural. For as "man" signifies "one that has humanity," so God signifies "one that has Godhead." But the three persons are three who have Godhead. Therefore the three persons are "three Gods."

Objection 2: Further, Gn. 1:1, where it is said, "In the beginning God created heaven and earth," the Hebrew original has "Elohim," which may be rendered "Gods" or "Judges": and this word is used on account of the plurality of persons. Therefore the three persons are "several Gods," and not "one" God.

Objection 3: Further, this word "thing" when it is said absolutely, seems to belong to substance. But it is predicated of the three persons in the plural. For Augustine says (De Doctr. Christ. i, 5): "The things that are the objects of our future glory are the Father, Son and Holy Ghost." Therefore other essential names can be predicated in the plural of the three persons.

Objection 4: Further, as this word "God" signifies "a being who has Deity," so also this word "person" signifies a being subsisting in an intellectual nature. But we say there are three persons. So for the same reason we can say there are "three Gods."

On the contrary, It is said (Dt. 6:4): "Hear, O Israel, the Lord thy God is one God."

I answer that, Some essential names signify the essence after the manner of substantives; while others signify it after the manner of adjectives. Those which signify it as substantives are predicated of the three persons in the singular only, and not in the plural. Those which signify the essence as adjectives are predicated of the three persons in the plural. The reason of this is that substantives signify something by way of substance, while adjectives signify something by way of accident, which adheres to a subject. Now just as substance has existence of itself, so also it has of itself unity or multitude; wherefore the singularity or plurality of a substantive name depends upon the form signified by the name. But as accidents have their existence in a subject, so they have unity or plurality from their subject; and therefore the singularity and plurality of adjectives depends upon their "supposita." In creatures, one form does not exist in several "supposita" except by unity of order, as the form of an ordered multitude. So if the names signifying such a form are substantives, they are predicated of many in the singular, but otherwise if they adjectives. For we say that many men are a college, or an army, or a people; but we say that many men are collegians. Now in God the divine essence is signified by way of a form, as above explained (Article 2), which, indeed, is simple and supremely one, as shown above (Question 3, Article 7; Question 11, Article 4). So, names which signify the divine essence in a substantive manner are predicated of the three persons in the singular, and not in the plural. This, then, is the reason why we say that Socrates, Plato and Cicero are "three men"; whereas we do not say the Father, Son and Holy Ghost are "three Gods," but "one God"; forasmuch as in the three "supposita" of human nature there are three humanities, whereas in the three divine Persons there is but one divine essence. On the other hand, the names which signify essence in an adjectival manner are predicated of the three persons plurally, by reason of the plurality of "supposita." For we say there are three "existent" or three "wise" beings, or three "eternal," "uncreated," and "immense" beings, if these terms are understood in an adjectival sense. But if taken in a substantive sense, we say "one uncreated, immense, eternal being," as Athanasius declares.

Reply to Objection 1: Though the name "God" signifies a being having Godhead, nevertheless the mode of signification is different. For the name "God" is used substantively; whereas "having Godhead" is used adjectively. Consequently, although there are "three having Godhead," it does not follow that there are three Gods.

Reply to Objection 2: Various languages have diverse modes of expression. So as by reason of the plurality of "supposita" the Greeks said "three hypostases," so also in Hebrew "Elohim" is in the plural. We, however, do not apply the plural either to "God" or to "substance," lest plurality be referred to the substance.

Reply to Objection 3: This word "thing" is one of the transcendentals. Whence, so far as it is referred to relation, it is predicated of God in the plural; whereas, so far as it is referred to the substance, it is predicated in the singular. So Augustine says, in the passage quoted, that "the same Trinity is a thing supreme."

Reply to Objection 4: The form signified by the word "person" is not essence or nature, but personality. So, as there are three personalities---that is, three personal properties in the Father, Son and Holy Ghost---it is predicated of the three, not in the singular, but in the plural.

Articulus 3

Argumentum 1

Ad tertium sic proceditur. Videtur quod nomina essentialia, ut hoc nomen deus, non praedicentur singulariter de tribus personis, sed pluraliter. Sicut enim homo significatur ut habens humanitatem, ita deus significatur ut habens deitatem. Sed tres personae sunt tres habentes deitatem.

Ergo tres personae sunt tres dii.

Argumentum 2

Praeterea, Gen. I, ubi dicitur, in principio creavit deus caelum et terram, Hebraica veritas habet elohim, quod potest interpretari dii, sive iudices.

Et hoc dicitur propter pluralitatem personarum.

Ergo tres personae sunt plures dii, et non unus deus.

Argumentum 3

Praeterea, hoc nomen res, cum absolute dicatur, videtur ad substantiam pertinere. Sed hoc nomen pluraliter praedicatur de tribus personis, dicit enim Augustinus, in libro de doctr. Christ., res quibus fruendum est, sunt pater et filius et spiritus sanctus.

Ergo et alia nomina essentialia pluraliter praedicari possunt de tribus personis.

Argumentum 4

Praeterea, sicut hoc nomen deus significat habentem deitatem, ita hoc nomen persona significat subsistentem in natura aliqua intellectuali. Sed dicimus tres personas.

Ergo, eadem ratione, dicere possumus tres deos.

Sed Contra

Sed contra est quod dicitur Deut. VI, audi, Israel, dominus deus tuus, deus unus est.

Corpus

Respondeo dicendum quod nominum essentialium quaedam significant essentiam substantive, quaedam vero adiective. Ea quidem quae substantive essentiam significant, praedicantur de tribus personis singulariter tantum, et non pluraliter, quae vero adiective essentiam significant, praedicantur de tribus personis in plurali.

Cuius ratio est, quia nomina substantiva significant aliquid per modum substantiae, nomina vero adiectiva significant aliquid per modum accidentis, quod inhaeret subiecto. Substantia autem, sicut per se habet esse, ita per se habet unitatem vel multitudinem, unde et singularitas vel pluralitas nominis substantivi attenditur secundum formam significatam per nomen.

Accidentia autem, sicut esse habent in subiecto, ita ex subiecto suscipiunt unitatem et multitudinem, et ideo in adiectivis attenditur singularitas et pluralitas secundum supposita.

In creaturis autem non invenitur una forma in pluribus suppositis nisi unitate ordinis, ut forma multitudinis ordinatae. Unde nomina significantia talem formam, si sint substantiva, praedicantur de pluribus in singulari, non autem si sint adiectiva. Dicimus enim quod multi homines sunt collegium vel exercitus aut populus, dicimus tamen quod plures homines sunt collegiati. In divinis autem essentia divina significatur per modum formae, ut dictum est quae quidem simplex est et maxime una, ut supra ostensum est.

Unde nomina significantia divinam essentiam substantive, singulariter, et non pluraliter, de tribus personis praedicantur.

Haec igitur est ratio quare socratem et Platonem et ciceronem dicimus tres homines; patrem autem et filium et spiritum sanctum non dicimus tres deos, sed unum deum, quia in tribus suppositis humanae naturae sunt tres humanitates; in tribus autem personis est una divina essentia. Ea vero quae significant essentiam adiective, praedicantur pluraliter de tribus, propter pluralitatem suppositorum. Dicimus enim tres existentes vel tres sapientes, aut tres aeternos et increatos et immensos, si adiective sumantur. Si vero substantive sumantur, dicimus unum increatum, immensum et aeternum, ut Athanasius dicit.

Ad 1

Ad primum ergo dicendum quod, licet deus significet habentem deitatem, est tamen alius modus significandi, nam deus dicitur substantive, sed habens deitatem dicitur adiective. Unde, licet sint tres habentes deitatem, non tamen sequitur quod sint tres dii.

Ad 2

Ad secundum dicendum quod diversae linguae habent diversum modum loquendi.

Unde, sicut propter pluralitatem suppositorum Graeci dicunt tres hypostases, ita et in Hebraeo dicitur pluraliter elohim.

Nos autem non dicimus pluraliter neque deos neque substantias, ne pluralitas ad substantiam referatur.

Ad 3

Ad tertium dicendum quod hoc nomen res est de transcendentibus.

Unde, secundum quod pertinet ad relationem, pluraliter praedicatur in divinis, secundum vero quod pertinet ad substantiam, singulariter praedicatur.

Unde Augustinus dicit ibidem quod eadem trinitas quaedam summa res est.

Ad 4

Ad quartum dicendum quod forma significata per hoc nomen persona, non est essentia vel natura, sed personalitas. Unde, cum sint tres personalitates, idest tres personales proprietates, in patre et filio et spiritu sancto, non singulariter, sed pluraliter praedicatur de tribus.