Thomas Aquinas, Summa Theologiae

Objection 1: It would seem that the human nature was united to the Word of God accidentally. For the Apostle says (Phil. 2:7) of the Son of God, that He was "in habit found as a man." But habit is accidentally associated with that to which it pertains, whether habit be taken for one of the ten predicaments or as a species of quality. Therefore human nature is accidentally united to the Son of God.

Objection 2: Further, whatever comes to a thing that is complete in being comes to it accidentally, for an accident is said to be what can come or go without the subject being corrupted. But human nature came to Christ in time, Who had perfect being from eternity. Therefore it came to Him accidentally.

Objection 3: Further, whatever does not pertain to the nature or the essence of a thing is its accident, for whatever is, is either a substance or an accident. But human nature does not pertain to the Divine Essence or Nature of the Son of God, for the union did not take place in the nature, as was said above (Article 1). Hence the human nature must have accrued accidentally to the Son of God.

Objection 4: Further, an instrument accrues accidentally. But the human nature was the instrument of the Godhead in Christ, for Damascene says (De Fide Orth. iii, 15), that "the flesh of Christ is the instrument of the Godhead." Therefore it seems that the human nature was united to the Son of God accidentally.

On the contrary, Whatever is predicated accidentally, predicates, not substance, but quantity, or quality, or some other mode of being. If therefore the human nature accrues accidentally, when we say Christ is man, we do not predicate substance, but quality or quantity, or some other mode of being, which is contrary to the Decretal of Pope Alexander III, who says (Conc. Later. iii): "Since Christ is perfect God and perfect man, what foolhardiness have some to dare to affirm that Christ as man is not a substance?"

I answer that, In evidence of this question we must know that two heresies have arisen with regard to the mystery of the union of the two natures in Christ. The first confused the natures, as Eutyches and Dioscorus, who held that from the two natures one nature resulted, so that they confessed Christ to be "from" two natures (which were distinct before the union), but not "in" two natures (the distinction of nature coming to an end after the union). The second was the heresy of Nestorius and Theodore of Mopsuestia, who separated the persons. For they held the Person of the Son of God to be distinct from the Person of the Son of man, and said these were mutually united: first, "by indwelling," inasmuch as the Word of God dwelt in the man, as in a temple; secondly, "by unity of intention," inasmuch as the will of the man was always in agreement with the will of the Word of God; thirdly, "by operation," inasmuch as they said the man was the instrument of the Word of God; fourthly, "by greatness of honor," inasmuch as all honor shown to the Son of God was equally shown to the Son of man, on account of His union with the Son of God; fifthly, "by equivocation," i.e. communication of names, inasmuch as we say that this man is God and the Son of God. Now it is plain that these modes imply an accidental union.

But some more recent masters, thinking to avoid these heresies, through ignorance fell into them. For some conceded one person in Christ, but maintained two hypostases, or two supposita, saying that a man, composed of body and soul, was from the beginning of his conception assumed by the Word of God. And this is the first opinion set down by the Master (Sent. iii, D, 6). But others desirous of keeping the unity of person, held that the soul of Christ was not united to the body, but that these two were mutually separate, and were united to the Word accidentally, so that the number of persons might not be increased. And this is the third opinion which the Master sets down (Sent. iii, D, 6).

But both of these opinions fall into the heresy of Nestorius; the first, indeed, because to maintain two hypostases or supposita in Christ is the same as to maintain two persons, as was shown above (Article 3). And if stress is laid on the word "person," we must have in mind that even Nestorius spoke of unity of person on account of the unity of dignity and honor. Hence the fifth Council (Constantinople II, coll. viii, can. 5) directs an anathema against such a one as holds "one person in dignity, honor and adoration, as Theodore and Nestorius foolishly wrote." But the other opinion falls into the error of Nestorius by maintaining an accidental union. For there is no difference in saying that the Word of God is united to the Man Christ by indwelling, as in His temple (as Nestorius said), or by putting on man, as a garment, which is the third opinion; rather it says something worse than Nestorius---to wit, that the soul and body are not united.

Now the Catholic faith, holding the mean between the aforesaid positions, does not affirm that the union of God and man took place in the essence or nature, nor yet in something accidental, but midway, in a subsistence or hypostasis. Hence in the fifth Council (Constantinople II, coll. viii, can. 5) we read: "Since the unity may be understood in many ways, those who follow the impiety of Apollinaris and Eutyches, professing the destruction of what came together" (i.e. destroying both natures), "confess a union by mingling; but the followers of Theodore and Nestorius, maintaining division, introduce a union of purpose. But the Holy Church of God, rejecting the impiety of both these treasons, confesses a union of the Word of God with flesh, by composition, which is in subsistence." Therefore it is plain that the second of the three opinions, mentioned by the Master (Sent. iii, D, 6), which holds one hypostasis of God and man, is not to be called an opinion, but an article of Catholic faith. So likewise the first opinion which holds two hypostases, and the third which holds an accidental union, are not to be styled opinions, but heresies condemned by the Church in Councils.

Reply to Objection 1: As Damascene says (De Fide Orth. iii, 26): "Examples need not be wholly and at all points similar, for what is wholly similar is the same, and not an example, and especially in Divine things, for it is impossible to find a wholly similar example in the Theology," i.e. in the Godhead of Persons, "and in the Dispensation," i.e. the mystery of the Incarnation. Hence the human nature in Christ is likened to a habit, i.e. a garment, not indeed in regard to accidental union, but inasmuch as the Word is seen by the human nature, as a man by his garment, and also inasmuch as the garment is changed, for it is shaped according to the figure of him who puts it on, and yet he is not changed from his form on account of the garment. So likewise the human nature assumed by the Word of God is ennobled, but the Word of God is not changed, as Augustine says (Qq. 83, qu. 73).

Reply to Objection 2: Whatever accrues after the completion of the being comes accidentally, unless it be taken into communion with the complete being, just as in the resurrection the body comes to the soul which pre-exists, yet not accidentally, because it is assumed unto the same being, so that the body has vital being through the soul; but it is not so with whiteness, for the being of whiteness is other than the being of man to which whiteness comes. But the Word of God from all eternity had complete being in hypostasis or person; while in time the human nature accrued to it, not as if it were assumed unto one being inasmuch as this is of the nature (even as the body is assumed to the being of the soul), but to one being inasmuch as this is of the hypostasis or person. Hence the human nature is not accidentally united to the Son of God.

Reply to Objection 3: Accident is divided against substance. Now substance, as is plain from Metaph. v, 25, is taken in two ways: first, for essence or nature; secondly, for suppositum or hypostasis---hence the union having taken place in the hypostasis, is enough to show that it is not an accidental union, although the union did not take place in the nature.

Reply to Objection 4: Not everything that is assumed as an instrument pertains to the hypostasis of the one who assumes, as is plain in the case of a saw or a sword; yet nothing prevents what is assumed into the unity of the hypostasis from being as an instrument, even as the body of man or his members. Hence Nestorius held that the human nature was assumed by the Word merely as an instrument, and not into the unity of the hypostasis. And therefore he did not concede that the man was really the Son of God, but His instrument. Hence Cyril says (Epist. ad Monach. Aegyptii): "The Scripture does not affirm that this Emmanuel," i.e. Christ, "was assumed for the office of an instrument, but as God truly humanized," i.e. made man. But Damascene held that the human nature in Christ is an instrument belonging to the unity of the hypostasis.

Articulus 6

Argumentum 1

Ad sextum sic proceditur. Videtur quod humana natura fuerit unita verbo dei accidentaliter.

Dicit enim apostolus, philipp. II, de filio dei, quod habitu inventus est ut homo.

Sed habitus accidentaliter advenit ei cuius est, sive accipiatur habitus prout est unum de decem generibus; sive prout est species qualitatis. Ergo humana natura accidentaliter unita est filio dei.

Argumentum 2

Praeterea, omne quod advenit alicui post esse completum, advenit ei accidentaliter, hoc enim dicimus accidens quod potest alicui et adesse et abesse praeter subiecti corruptionem. Sed natura humana advenit ex tempore filio dei habenti esse perfectum ab aeterno. Ergo advenit ei accidentaliter.

Argumentum 3

Praeterea, quidquid non pertinet ad naturam seu essentiam alicuius rei, est accidens eius, quia omne quod est vel est substantia, vel est accidens. Sed humana natura non pertinet ad essentiam vel naturam filii dei divinam, quia non est facta unio in natura, ut supra dictum est.

Ergo oportet quod natura humana accidentaliter filio dei advenerit.

Argumentum 4

Praeterea, instrumentum accidentaliter advenit. Sed natura humana in christo fuit divinitatis instrumentum, dicit enim Damascenus, in III libro, quod caro christi instrumentum divinitatis existit.

Ergo videtur quod humana natura fuerit filio dei unita accidentaliter.

Sed Contra

Sed contra est quod illud quod accidentaliter praedicatur, non praedicat aliquid, sed quantum vel quale vel aliquo modo se habens si igitur humana natura accidentaliter adveniret, cum dicitur christus esse homo, non praedicaretur aliquid, sed quale aut quantum aut aliquo modo se habens.

Quod est contra decretalem Alexandri Papae dicentis, cum christus sit perfectus deus et perfectus homo, qua temeritate audent quidam dicere quod christus, secundum quod est homo, non est aliquid?

Corpus

Respondeo dicendum quod, ad huius quaestionis evidentiam, sciendum est quod circa mysterium unionis duarum naturarum in christo, duplex haeresis insurrexit. Una quidem confundentium naturas, sicut eutychetis et dioscori, qui posuerunt quod ex duabus naturis est constituta una natura; ita quod confitentur christum esse ex duabus naturis, quasi ante unionem distinctis; non autem in duabus naturis, quasi post unionem naturarum distinctione cessante.

Alia vero fuit haeresis Nestorii et theodori Mopsuesteni separantium personas. Posuerunt enim aliam esse personam filii dei, et filii hominis. Quas dicebant sibi invicem esse unitas, primo quidem, secundum inhabitationem, inquantum scilicet verbum dei habitavit in illo homine sicut in templo. Secundo, secundum unitatem affectus, inquantum scilicet voluntas illius hominis est semper conformis voluntati dei. Tertio modo, secundum operationem, prout scilicet dicebant hominem illum esse dei verbi instrumentum. Quarto, secundum dignitatem honoris, prout omnis honor qui exhibetur filio dei, exhibetur filio hominis, propter coniunctionem ad filium dei. Quinto, secundum aequivocationem, idest secundum communicationem nominum, prout scilicet dicimus illum hominem esse deum et filium dei.

Manifestum est autem omnes istos modos accidentalem unionem importare. Quidam autem posteriores magistri, putantes se has haereses declinare, in eas per ignorantiam inciderunt.

Quidam enim eorum concesserunt unam christi personam, sed posuerunt duas hypostases, sive duo supposita; dicentes hominem quendam, compositum ex anima et corpore, a principio suae conceptionis esse assumptum a dei verbo.

Et haec est prima opinio quam magister ponit in sexta distinctione tertii libri sententiarum.

Alii vero, volentes servare unitatem personae, posuerunt christi animam non esse corpori unitam, sed haec duo, separata ab invicem, esse unita verbo accidentaliter, ut sic non cresceret numerus personarum.

Et haec est tertia opinio quam magister ibidem ponit.

Utraque autem harum opinionum incidit in haeresim Nestorii.

Prima quidem, quia idem est ponere duas hypostases vel duo supposita in christo, quod ponere duas personas, ut supra dictum est.

Et si fiat vis in nomine personae, considerandum est quod etiam Nestorius utebatur unitate personae, propter unitatem dignitatis et honoris.

Unde et quinta synodus definit anathema eum qui dicit unam personam secundum dignitatem, honorem et adorationem, sicut theodorus et Nestorius insanientes conscripserunt.

Alia vero opinio incidit in errorem Nestorii quantum ad hoc, quod posuit unionem accidentalem. Non enim differt dicere quod verbum dei unitum est homini christo secundum inhabitationem sicut in templo suo, sicut dicebat Nestorius; et dicere quod unitum fuit verbum homini secundum induitionem sicut vestimento, sicut dicit tertia opinio. Quae etiam dicit peius aliquid quam Nestorius, quod anima et corpus non sunt unita.

Fides autem catholica, medium tenens inter praedictas positiones, neque dicit esse unionem factam dei et hominis secundum essentiam vel naturam; neque etiam secundum accidens; sed medio modo, secundum subsistentiam seu hypostasim.

Unde in quinta synodo legitur, cum multis modis unitas intelligatur, qui iniquitatem Apollinarii et eutychetis sequuntur, interemptionem eorum quae convenerunt colentes, (idest, interimentes utramque naturam), unionem secundum confusionem dicunt; theodori autem et Nestorii sequaces, divisione gaudentes, affectualem unitatem introducunt, sancta vero dei ecclesia, utriusque perfidiae impietatem reiiciens unionem dei verbi ad carnem secundum compositionem confitetur, quod est secundum subsistentiam.

Sic igitur patet quod secunda trium opinionum quas magister ponit, quae asserit unam hypostasim dei et hominis, non est dicenda opinio, sed sententia catholicae fidei.

Similiter etiam prima opinio, quae ponit duas hypostases; et tertia, quae ponit unionem accidentalem; non sunt dicendae opiniones, sed haereses in Conciliis ab ecclesia damnatae.

Ad 1

Ad primum ergo dicendum quod, sicut Damascenus dicit, in III libro, non necesse autem omnifariam et indefective assimilari exempla, quod enim in omnibus simile, idem utique erit, et non exemplum.

Et maxime in divinis, impossibile enim simile exemplum invenire et in theologia, idest in deitate personarum, et in dispensatione, idest in mysterio incarnationis. Humana igitur natura in christo assimilatur habitui, idest vestimento, non quidem quantum ad accidentalem unionem, sed quantum ad hoc, quod verbum videtur per humanam naturam, sicut homo per vestimentum. Et etiam quantum ad hoc, quod vestimentum mutatur, quia scilicet formatur secundum figuram eius qui induit ipsum, qui a sua forma non mutatur propter vestimentum, et similiter humana natura assumpta a verbo dei est meliorata, ipsum autem verbum dei non est mutatum; ut exponit Augustinus, in libro octogintatrium quaestionum.

Ad 2

Ad secundum dicendum quod illud quod advenit post esse completum, accidentaliter advenit, nisi trahatur in communionem illius esse completi. Sicut in resurrectione corpus adveniet animae praeexistenti, non tamen accidentaliter, quia ad idem esse assumetur, ut scilicet corpus habeat esse vitale per animam. Non est autem sic de albedine, quia aliud est esse albi, et aliud esse hominis cui advenit albedo. Verbum autem dei ab aeterno esse completum habuit secundum hypostasim sive personam, ex tempore autem advenit ei natura humana, non quasi assumpta ad unum esse prout est naturae, sicut corpus assumitur ad esse animae; sed ad unum esse prout est hypostasis vel personae. Et ideo humana natura non unitur accidentaliter filio dei.

Ad 3

Ad tertium dicendum quod accidens dividitur contra substantiam.

Substantia autem, ut patet V metaphys., dupliciter dicitur, uno modo, essentia sive natura; alio modo, pro supposito sive hypostasi.

Unde sufficit ad hoc quod non sit unio accidentalis, quod sit facta unio secundum hypostasim, licet non sit facta unio secundum naturam.

Ad 4

Ad quartum dicendum quod non omne quod assumitur ut instrumentum, pertinet ad hypostasim assumentis, sicut patet de securi et gladio nihil tamen prohibet illud quod assumitur ad unitatem hypostasis, se habere ut instrumentum, sicut corpus hominis vel membra eius.

Nestorius igitur posuit quod natura humana est assumpta a verbo solum per modum instrumenti, non autem ad unitatem hypostasis. Et ideo non concedebat quod homo ille vere esset filius dei, sed instrumentum eius.

Unde Cyrillus dicit, in epistola ad monachos Aegypti, hunc emanuelem, idest christum, non tanquam instrumenti officio sumptum dicit Scriptura, sed tanquam deum vere humanatum, idest hominem factum.

Damascenus autem posuit naturam humanam in christo esse sicut instrumentum ad unitatem hypostasis pertinens.