Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that the Son is not other than the Father. For "other" is a relative term implying diversity of substance. If, then, the Son is other than the Father, He must be different from the Father; which is contrary to what Augustine says (De Trin. vii), that when we speak of three persons, "we do not mean to imply diversity."

Objection 2: Further, whosoever are other from one another, differ in some way from one another. Therefore, if the Son is other than the Father, it follows that He differs from the Father; which is against what Ambrose says (De Fide i), that "the Father and the Son are one in Godhead; nor is there any difference in substance between them, nor any diversity."

Objection 3: Further, the term alien is taken from "alius" . But the Son is not alien from the Father, for Hilary says (De Trin. vii) that "in the divine persons there is nothing diverse, nothing alien, nothing separable." Therefore the Son is not other that the Father.

Objection 4: Further, the terms "other person" and "other thing" have the same meaning, differing only in gender. So if the Son is another person from the Father, it follows that the Son is a thing apart from the Father.

On the contrary, Augustine says: "There is one essence of the Father and Son and Holy Ghost, in which the Father is not one thing, the Son another, and the Holy Ghost another; although the Father is one person, the Son another, and the Holy Ghost another."

I answer that, Since as Jerome remarks , a heresy arises from words wrongly used, when we speak of the Trinity we must proceed with care and with befitting modesty; because, as Augustine says (De Trin. i, 3), "nowhere is error more harmful, the quest more toilsome, the finding more fruitful." Now, in treating of the Trinity, we must beware of two opposite errors, and proceed cautiously between them---namely, the error of Arius, who placed a Trinity of substance with the Trinity of persons; and the error of Sabellius, who placed unity of person with the unity of essence.

Thus, to avoid the error of Arius we must shun the use of the terms diversity and difference in God, lest we take away the unity of essence: we may, however, use the term "distinction" on account of the relative opposition. Hence whenever we find terms of "diversity" or "difference" of Persons used in an authentic work, these terms of "diversity" or "difference" are taken to mean "distinction." But lest the simplicity and singleness of the divine essence be taken away, the terms "separation" and "division," which belong to the parts of a whole, are to be avoided: and lest quality be taken away, we avoid the use of the term "disparity": and lest we remove similitude, we avoid the terms "alien" and "discrepant." For Ambrose says (De Fide i) that "in the Father and the Son there is no discrepancy, but one Godhead": and according to Hilary, as quoted above, "in God there is nothing alien, nothing separable."

To avoid the heresy of Sabellius, we must shun the term "singularity," lest we take away the communicability of the divine essence. Hence Hilary says (De Trin. vii): "It is sacrilege to assert that the Father and the Son are separate in Godhead." We must avoid the adjective "only" lest we take away the number of persons. Hence Hilary says in the same book: "We exclude from God the idea of singularity or uniqueness." Nevertheless, we say "the only Son," for in God there is no plurality of Sons. Yet, we do not say "the only God," for the Deity is common to several. We avoid the word "confused," lest we take away from the Persons the order of their nature. Hence Ambrose says (De Fide i): "What is one is not confused; and there is no multiplicity where there is no difference." The word "solitary" is also to be avoided, lest we take away the society of the three persons; for, as Hilary says (De Trin. iv), "We confess neither a solitary nor a diverse God."

This word "other" , however, in the masculine sense, means only a distinction of "suppositum"; and hence we can properly say that "the Son is other than the Father," because He is another "suppositum" of the divine nature, as He is another person and another hypostasis.

Reply to Objection 1: "Other," being like the name of a particular thing, refers to the "suppositum"; and so, there is sufficient reason for using it, where there is a distinct substance in the sense of hypostasis or person. But diversity requires a distinct substance in the sense of essence. Thus we cannot say that the Son is diverse from the Father, although He is another.

Reply to Objection 2: "Difference" implies distinction of form. There is one form in God, as appears from the text, "Who, when He was in the form of God" (Phil. 2:6). Therefore the term "difference" does not properly apply to God, as appears from the authority quoted. Yet, Damascene (De Fide Orth. i, 5) employs the term "difference" in the divine persons, as meaning that the relative property is signified by way of form. Hence he says that the hypostases do not differ from each other in substance, but according to determinate properties. But "difference" is taken for "distinction," as above stated.

Reply to Objection 3: The term "alien" means what is extraneous and dissimilar; which is not expressed by the term "other" ; and therefore we say that the Son is "other" than the Father, but not that He is anything "alien."

Reply to Objection 4: The neuter gender is formless; whereas the masculine is formed and distinct; and so is the feminine. So the common essence is properly and aptly expressed by the neuter gender, but by the masculine and feminine is expressed the determined subject in the common nature. Hence also in human affairs, if we ask, Who is this man? we answer, Socrates, which is the name of the "suppositum"; whereas, if we ask, What is he? we reply, A rational and mortal animal. So, because in God distinction is by the persons, and not by the essence, we say that the Father is other than the Son, but not something else; while conversely we say that they are one thing, but not one person.

Articulus 2

Argumentum 1

Ad secundum sic proceditur. Videtur quod filius non sit alius a patre. Alius enim est relativum diversitatis substantiae.

Si igitur filius est alius a patre, videtur quod sit a patre diversus.

Quod est contra Augustinum, VII de Trin., ubi dicit quod, cum dicimus tres personas, non diversitatem intelligere volumus.

Argumentum 2

Praeterea, quicumque sunt alii ab invicem, aliquo modo ab invicem differunt. Si igitur filius est alius a patre, sequitur quod sit differens a patre.

Quod est contra Ambrosium, in I de fide, ubi ait, pater et filius deitate unum sunt, nec est ibi substantiae differentia, neque ulla diversitas.

Argumentum 3

Praeterea, ab alio alienum dicitur. Sed filius non est alienus a patre, dicit enim Hilarius, in VII de Trin., quod in divinis personis nihil est diversum, nihil alienum, nihil separabile.

Ergo filius non est alius a patre.

Argumentum 4

Praeterea, alius et aliud idem significant, sed sola generis consignificatione differunt. Si ergo filius est alius a patre, videtur sequi quod filius sit aliud a patre.

Sed Contra

Sed contra est quod Augustinus dicit, in libro de fide ad Petrum, una est enim essentia patris et filii et spiritus sancti, in qua non est aliud pater, aliud filius, aliud spiritus sanctus; quamvis personaliter sit alius pater, alius filius, alius spiritus sanctus.

Corpus

Respondeo dicendum quod, quia ex verbis inordinate prolatis incurritur haeresis, ut Hieronymus dicit, ideo cum de trinitate loquimur, cum cautela et modestia est agendum, quia, ut Augustinus dicit, in I de Trin., nec periculosius alicubi erratur, nec laboriosius aliquid quaeritur, nec fructuosius aliquid invenitur.

Oportet autem in his quae de trinitate loquimur, duos errores oppositos cavere, temperate inter utrumque procedentes, scilicet errorem Arii, qui posuit cum trinitate personarum trinitatem substantiarum; et errorem Sabellii, qui posuit cum unitate essentiae unitatem personae.

Ad evitandum igitur errorem Arii, vitare debemus in divinis nomen diversitatis et differentiae, ne tollatur unitas essentiae, possumus autem uti nomine distinctionis, propter oppositionem relativam. Unde sicubi in aliqua Scriptura authentica diversitas vel differentia personarum invenitur, sumitur diversitas vel differentia pro distinctione. Ne autem tollatur simplicitas divinae essentiae, vitandum est nomen separationis et divisionis, quae est totius in partes. Ne autem tollatur aequalitas, vitandum est nomen disparitatis. Ne vero tollatur similitudo, vitandum est nomen alieni et discrepantis, dicit enim Ambrosius, in libro de fide, quod in patre et filio non est discrepans, sed una divinitas, et secundum Hilarium, ut dictum est, in divinis nihil est alienum, nihil separabile.

Ad vitandum vero errorem Sabellii, vitare debemus singularitatem, ne tollatur communicabilitas essentiae divinae, unde Hilarius dicit, VII de Trin., patrem et filium singularem deum praedicare, sacrilegum est.

Debemus etiam vitare nomen unici, ne tollatur numerus personarum, unde Hilarius in eodem libro dicit quod a deo excluditur singularis atque unici intelligentia.

Dicimus tamen unicum filium, quia non sunt plures filii in divinis.

Neque tamen dicimus unicum deum, quia pluribus deitas est communis vitamus etiam nomen confusi, ne tollatur ordo naturae a personis, unde Ambrosius dicit, I de fide, neque confusum est quod unum est, neque multiplex esse potest quod indifferens est.

Vitandum est etiam nomen solitarii, ne tollatur consortium trium personarum, dicit enim Hilarius, in IV de Trin., nobis neque solitarius, neque diversus deus est confitendus.

Hoc autem nomen alius, masculine sumptum, non importat nisi distinctionem suppositi. Unde convenienter dicere possumus quod filius est alius a patre, quia scilicet est aliud suppositum divinae naturae, sicut est alia persona, et alia hypostasis.

Ad 1

Ad primum ergo dicendum quod alius, quia est sicut quoddam particulare nomen, tenet se ex parte suppositi, unde ad eius rationem sufficit distinctio substantiae quae est hypostasis vel persona. Sed diversitas requirit distinctionem substantiae quae est essentia. Et ideo non possumus dicere quod filius sit diversus a patre, licet sit alius.

Ad 2

Ad secundum dicendum quod differentia importat distinctionem formae. Est autem tantum una forma in divinis, ut patet per id quod dicitur Philip. II, qui cum in forma dei esset.

Et ideo nomen differentis non proprie competit in divinis, ut patet per auctoritatem inductam. Utitur tamen Damascenus nomine differentiae in divinis personis, secundum quod proprietas relativa significatur per modum formae, unde dicit quod non differunt ab invicem hypostases secundum substantiam, sed secundum determinatas proprietates.

Sed differentia sumitur pro distinctione, ut dictum est.

Ad 3

Ad tertium dicendum quod alienum est quod est extraneum et dissimile. Sed hoc non importatur cum dicitur alius. Et ideo dicimus filium alium a patre, licet non dicamus alienum.

Ad 4

Ad quartum dicendum quod neutrum genus est informe, masculinum autem est formatum et distinctum, et similiter femininum. Et ideo convenienter per neutrum genus significatur essentia communis, per masculinum autem et femininum, aliquod suppositum determinatum in communi natura. Unde etiam in rebus humanis, si quaeratur, quis est iste? respondetur, socrates, quod nomen est suppositi, si autem quaeratur, quid est iste? respondetur, animal rationale et mortale. Et ideo, quia in divinis distinctio est secundum personas, non autem secundum essentiam, dicimus quod pater est alius a filio, sed non aliud, et e converso dicimus quod sunt unum, sed non unus.