Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that two Divine Persons cannot assume one and the same individual nature. For, this being granted, there would either be several men or one. But not several, for just as one Divine Nature in several Persons does not make several gods, so one human nature in several persons does not make several men. Nor would there be only one man, for one man is "this man," which signifies one person; and hence the distinction of three Divine Persons would be destroyed, which cannot be allowed. Therefore neither two nor three Persons can take one human nature.

Objection 2: Further, the assumption is terminated in the unity of Person, as has been said above (Article 2). But the Father, Son, and Holy Ghost are not one Person. Therefore the three Persons cannot assume one human nature.

Objection 3: Further, Damascene says (De Fide Orth. iii, 3,4), and Augustine (De Trin. i, 11,12,13), that from the Incarnation of God the Son it follows that whatever is said of the Son of God is said of the Son of Man, and conversely. Hence, if three Persons were to assume one human nature, it would follow that whatever is said of each of the three Persons would be said of the man; and conversely, what was said of the man could be said of each of the three Persons. Therefore what is proper to the Father, viz. to beget the Son, would be said of the man, and consequently would be said of the Son of God; and this could not be. Therefore it is impossible that the three Persons should assume one human nature.

On the contrary, The Incarnate Person subsists in two natures. But the three Persons can subsist in one Divine Nature. Therefore they can also subsist in one human nature in such a way that the human nature be assumed by the three Persons.

I answer that, As was said above (Question 2, Article 5, ad 1), by the union of the soul and body in Christ neither a new person is made nor a new hypostasis, but one human nature is assumed to the Divine Person or hypostasis, which, indeed, does not take place by the power of the human nature, but by the power of the Divine Person. Now such is the characteristic of the Divine Persons that one does not exclude another from communicating in the same nature, but only in the same Person. Hence, since in the mystery of the Incarnation "the whole reason of the deed is the power of the doer," as Augustine says (Ep. ad Volusianum cxxxvii), we must judge of it in regard to the quality of the Divine Person assuming, and not according to the quality of the human nature assumed. Therefore it is not impossible that two or three Divine Persons should assume one human nature, but it would be impossible for them to assume one human hypostasis or person; thus Anselm says in the book De Concep. Virg. (Cur Deus Homo ii, 9), that "several Persons cannot assume one and the same man to unity of Person."

Reply to Objection 1: In the hypothesis that three Persons assume one human nature, it would be true to say that the three Persons were one man, because of the one human nature. For just as it is now true to say the three Persons are one God on account of the one Divine Nature, so it would be true to say they are one man on account of the one human nature. Nor would "one" imply unity of person, but unity in human nature; for it could not be argued that because the three Persons were one man they were one simply. For nothing hinders our saying that men, who are many simply, are in some respect one, e.g. one people, and as Augustine says (De Trin. vi, 3): "The Spirit of God and the spirit of man are by nature different, but by inherence one spirit results," according to 1 Cor. 6:17: "He who is joined to the Lord is one spirit."

Reply to Objection 2: In this supposition the human nature would be assumed to the unity, not indeed of one Person, but to the unity of each Person, so that even as the Divine Nature has a natural unity with each Person, so also the human nature would have a unity with each Person by assumption.

Reply to Objection 3: In the mystery of the Incarnation, there results a communication of the properties belonging to the nature, because whatever belongs to the nature can be predicated of the Person subsisting in that nature, no matter to which of the natures it may apply. Hence in this hypothesis, of the Person of the Father may be predicated what belongs to the human nature and what belongs to the Divine; and likewise of the Person of the Son and of the Holy Ghost. But what belongs to the Person of the Father by reason of His own Person could not be attributed to the Person of the Son or Holy Ghost on account of the distinction of Persons which would still remain. Therefore it might be said that as the Father was unbegotten, so the man was unbegotten, inasmuch as "man" stood for the Person of the Father. But if one were to go on to say, "The man is unbegotten; the Son is man; therefore the Son is unbegotten," it would be the fallacy of figure of speech or of accident; even as we now say God is unbegotten, because the Father is unbegotten, yet we cannot conclude that the Son is unbegotten, although He is God.

Articulus 6

Argumentum 1

Ad sextum sic proceditur. Videtur quod duae personae divinae non possunt assumere unam et eandem numero naturam. Hoc enim supposito aut essent unus homo, vel plures. Sed non plures, sicut enim una natura divina in pluribus personis non patitur esse plures deos, ita una humana natura in pluribus personis non patitur esse plures homines. Similiter etiam non possent esse unus homo, quia unus homo est iste homo, qui demonstrat unam personam; et sic tolleretur distinctio trium personarum divinarum, quod est inconveniens. Non ergo duae aut tres personae possunt accipere unam naturam humanam.

Argumentum 2

Praeterea, assumptio terminatur ad unitatem personae, ut dictum est.

Sed non est una persona patris et filii et spiritus sancti. Ergo non possunt tres personae assumere unam naturam humanam.

Argumentum 3

Praeterea, Damascenus dicit, in III libro, et Augustinus, in I de Trin., quod ex incarnatione filii dei consequitur quod quidquid dicitur de filio dei, dicitur de filio hominis, et e converso.

Si ergo tres personae assumerent unam naturam humanam, sequitur quod quidquid dicitur de qualibet trium personarum, diceretur de illo homine, et e converso ea quae dicerentur de illo homine, possent dici de qualibet trium personarum. Sic ergo id quod est proprium patris, scilicet generare filium ab aeterno, diceretur de illo homine, et per consequens diceretur de filio dei, quod est inconveniens. Non ergo est possibile quod tres personae divinae assumant unam naturam humanam.

Sed Contra

Sed contra, persona incarnata subsistit in duabus naturis, divina scilicet et humana. Sed tres personae possunt subsistere in una natura divina. Ergo etiam possunt subsistere in una natura humana, ita scilicet quod sit una natura humana a tribus personis assumpta.

Corpus

Respondeo dicendum quod, sicut supra dictum est, ex unione animae et corporis in christo non fit neque nova persona neque hypostasis, sed fit una natura assumpta in personam vel hypostasim divinam. Quod quidem non fit per potentiam naturae humanae, sed per potentiam personae divinae. Est autem talis divinarum personarum conditio quod una earum non excludit aliam a communione eiusdem naturae, sed solum a communione eiusdem personae. Quia igitur in mysterio incarnationis tota ratio facti est potentia facientis, ut Augustinus dicit, in epistola ad volusianum; magis est circa hoc iudicandum secundum conditionem personae assumentis quam secundum conditionem naturae humanae assumptae. Sic igitur non est impossibile divinis personis ut duae vel tres assumant unam naturam humanam. Esset tamen impossibile ut assumerent unam hypostasim vel unam personam humanam, sicut Anselmus dicit, in libro de conceptu virginali, quod plures personae non possunt assumere unum eundemque hominem.

Ad 1

Ad primum ergo dicendum quod, hac positione facta, quod scilicet tres personae assumerent unam humanam naturam, verum esset dicere quod tres personae essent unus homo, propter unam humanam naturam, sicut nunc verum est dicere quod sunt unus deus, propter unam divinam naturam. Nec ly unus importat unitatem personae, sed unitatem in natura humana. Non enim posset argui ex hoc quod tres personae sunt unus homo, quod essent unus simpliciter, nihil enim prohibet dicere quod homines qui sunt plures simpliciter, sint unus quantum ad aliquid, puta unus populus; sicut Augustinus dicit, VI de Trin., diversum est natura spiritus hominis et spiritus dei, sed inhaerendo fit unus spiritus, secundum illud I Cor. VI, qui adhaeret deo, unus spiritus est.

Ad 2

Ad secundum dicendum quod, illa positione facta, humana natura esset assumpta in unitate non unius personae, sed in unitate singularum personarum, ita scilicet quod, sicut divina natura habet naturalem unitatem cum singulis personis, ita natura humana haberet unitatem cum singulis per assumptionem.

Ad 3

Ad tertium dicendum quod circa mysterium incarnationis fuit communicatio proprietatum pertinentium ad naturam, quia quaecumque conveniunt naturae, possunt praedicari de persona subsistente in natura illa, cuiuscumque naturae nomine significetur. Praedicta ergo positione facta, de persona patris poterunt praedicari et ea quae sunt humanae naturae, et ea quae sunt divinae, et similiter de persona filii et spiritus sancti. Non autem illud quod conveniret personae patris ratione propriae personae, posset attribui personae filii aut spiritus sancti, propter distinctionem personarum, quae remaneret. Posset ergo dici quod, sicut pater est ingenitus, ita homo esset ingenitus, secundum quod ly homo supponeret pro persona patris. Si quis autem ulterius procederet, homo est ingenitus, filius est homo, ergo filius est ingenitus, esset fallacia figurae dictionis vel accidentis. Sicut et nunc dicimus deum esse ingenitum, quia pater est ingenitus, nec tamen possumus concludere quod filius sit ingenitus, quamvis sit deus.