Thomas Aquinas, Summa Theologiae

Objection 1: It would seem there is not trinity in God. For every name in God signifies substance or relation. But this name "Trinity" does not signify the substance; otherwise it would be predicated of each one of the persons: nor does it signify relation; for it does not express a name that refers to another. Therefore the word "Trinity" is not to be applied to God.

Objection 2: Further, this word "trinity" is a collective term, since it signifies multitude. But such a word does not apply to God; as the unity of a collective name is the least of unities, whereas in God there exists the greatest possible unity. Therefore this word "trinity" does not apply to God.

Objection 3: Further, every trine is threefold. But in God there is not triplicity; since triplicity is a kind of inequality. Therefore neither is there trinity in God.

Objection 4: Further, all that exists in God exists in the unity of the divine essence; because God is His own essence. Therefore, if Trinity exists in God, it exists in the unity of the divine essence; and thus in God there would be three essential unities; which is heresy.

Objection 5: Further, in all that is said of God, the concrete is predicated of the abstract; for Deity is God and paternity is the Father. But the Trinity cannot be called trine; otherwise there would be nine realities in God; which, of course, is erroneous. Therefore the word trinity is not to be applied to God.

On the contrary, Athanasius says: "Unity in Trinity; and Trinity in Unity is to be revered."

I answer that, The name "Trinity" in God signifies the determinate number of persons. And so the plurality of persons in God requires that we should use the word trinity; because what is indeterminately signified by plurality, is signified by trinity in a determinate manner.

Reply to Objection 1: In its etymological sense, this word "Trinity" seems to signify the one essence of the three persons, according as trinity may mean trine-unity. But in the strict meaning of the term it rather signifies the number of persons of one essence; and on this account we cannot say that the Father is the Trinity, as He is not three persons. Yet it does not mean the relations themselves of the Persons, but rather the number of persons related to each other; and hence it is that the word in itself does not express regard to another.

Reply to Objection 2: Two things are implied in a collective term, plurality of the "supposita," and a unity of some kind of order. For "people" is a multitude of men comprehended under a certain order. In the first sense, this word "trinity" is like other collective words; but in the second sense it differs from them, because in the divine Trinity not only is there unity of order, but also with this there is unity of essence.

Reply to Objection 3: "Trinity" is taken in an absolute sense; for it signifies the threefold number of persons. "Triplicity" signifies a proportion of inequality; for it is a species of unequal proportion, according to Boethius (Arithm. i, 23). Therefore in God there is not triplicity, but Trinity.

Reply to Objection 4: In the divine Trinity is to be understood both number and the persons numbered. So when we say, "Trinity in Unity," we do not place number in the unity of the essence, as if we meant three times one; but we place the Persons numbered in the unity of nature; as the "supposita" of a nature are said to exist in that nature. On the other hand, we say "Unity in Trinity"; meaning that the nature is in its "supposita."

Reply to Objection 5: When we say, "Trinity is trine," by reason of the number implied, we signify the multiplication of that number by itself; since the word trine imports a distinction in the "supposita" of which it is spoken. Therefore it cannot be said that the Trinity is trine; otherwise it follows that, if the Trinity be trine, there would be three "supposita" of the Trinity; as when we say, "God is trine," it follows that there are three "supposita" of the Godhead.

Articulus 1

Argumentum 1

Ad primum sic proceditur. Videtur quod non sit trinitas in divinis. Omne enim nomen in divinis vel significat substantiam, vel relationem. Sed hoc nomen trinitas non significat substantiam, praedicaretur enim de singulis personis. Neque significat relationem, quia non dicitur secundum nomen ad aliud.

Ergo nomine trinitatis non est utendum in divinis.

Argumentum 2

Praeterea, hoc nomen trinitas videtur esse nomen collectivum, cum significet multitudinem. Tale autem nomen non convenit in divinis, cum unitas importata per nomen collectivum sit minima unitas, in divinis autem est maxima unitas.

Ergo hoc nomen trinitas non convenit in divinis.

Argumentum 3

Praeterea, omne trinum est triplex. Sed in deo non est triplicitas, cum triplicitas sit species inaequalitatis. Ergo nec trinitas.

Argumentum 4

Praeterea, quidquid est in deo, est in unitate essentiae divinae, quia deus est sua essentia. Si igitur trinitas est in deo, erit in unitate essentiae divinae. Et sic in deo erunt tres essentiales unitates, quod est haereticum.

Argumentum 5

Praeterea, in omnibus quae dicuntur de deo, concretum praedicatur de abstracto, deitas enim est deus, et paternitas est pater. Sed trinitas non potest dici trina, quia sic essent novem res in divinis, quod est erroneum. Ergo nomine trinitatis non est utendum in divinis.

Sed Contra

Sed contra est quod Athanasius dicit, quod unitas in trinitate, et trinitas in unitate veneranda sit.

Corpus

Respondeo dicendum quod nomen trinitatis in divinis significat determinatum numerum personarum. Sicut igitur ponitur pluralitas personarum in divinis, ita utendum est nomine trinitatis, quia hoc idem quod significat pluralitas indeterminate, significat hoc nomen trinitas determinate.

Ad 1

Ad primum ergo dicendum quod hoc nomen trinitas, secundum etymologiam vocabuli, videtur significare unam essentiam trium personarum, secundum quod dicitur trinitas quasi trium unitas.

Sed secundum proprietatem vocabuli, significat magis numerum personarum unius essentiae. Et propter hoc non possumus dicere quod pater sit trinitas, quia non est tres personae. Non autem significat ipsas relationes personarum, sed magis numerum personarum ad invicem relatarum. Et inde est quod, secundum nomen, ad aliud non refertur.

Ad 2

Ad secundum dicendum quod nomen collectivum duo importat, scilicet pluralitatem suppositorum, et unitatem quandam, scilicet ordinis alicuius, populus enim est multitudo hominum sub aliquo ordine comprehensorum. Quantum ergo ad primum, hoc nomen trinitas convenit cum nominibus collectivis, sed quantum ad secundum differt, quia in divina trinitate non solum est unitas ordinis, sed cum hoc est etiam unitas essentiae.

Ad 3

Ad tertium dicendum quod trinitas absolute dicitur, significat enim numerum ternarium personarum. Sed triplicitas significat proportionem inaequalitatis, est enim species proportionis inaequalis, sicut patet per boetium in arithmetica.

Et ideo non est in deo triplicitas, sed trinitas.

Ad 4

Ad quartum dicendum quod in trinitate divina intelligitur et numerus, et personae numeratae. Cum ergo dicimus trinitatem in unitate, non ponimus numerum in unitate essentiae, quasi sit ter una, sed personas numeratas ponimus in unitate naturae, sicut supposita alicuius naturae dicuntur esse in natura illa. E converso autem dicimus unitatem in trinitate, sicut natura dicitur esse in suis suppositis.

Ad 5

Ad quintum dicendum quod, cum dicitur, trinitas est trina, ratione numeri importati significatur multiplicatio eiusdem numeri in seipsum, cum hoc quod dico trinum, importet distinctionem in suppositis illius de quo dicitur. Et ideo non potest dici quod trinitas sit trina, quia sequeretur, si trinitas esset trina, quod tria essent supposita trinitatis; sicut cum dicitur, deus est trinus, sequitur quod sunt tria supposita deitatis.