Chapter 66 [!]
One should know that the hypostatic union produces one compound hypostasis of the thing united and that this preserves unconfused and unaltered in itself both the uniting natures and their difference as well as their natural properties, Moreover, this has no hypostatic difference with itself, because those characteristic differences of the things uniting, by which each of them is distinguished from others of the same species, become its own. Thus it is with the hypostasis in the case of the soul and the body, for here one hypostasis is made of both—the compound hypostasis of Peter, let us say, or of Paul. This keeps in itself the two perfect natures—that of the soul and that of the body— and it preserves their difference distinct and their properties unconfused. And in itself it has the characteristic differences of each, those of the soul, which distinguish it from all other souls, and those of the body, which distinguish it from all other bodies. These, however, in no wise separate the soul from the body, but they unite and bind them together, at the same time marking off the one hypostasis composed of them from all other hypostases of the same species. Moreover, once the natures become hypostatically united, they remain absolutely indivisible. And this is so because, even though the soul is separated from the body in death, the hypostasis of both remains one and the same. For the constitution in itself of each thing at its beginning of being is a hypostasis. Therefore, the body remains, as does the soul; both always having the one principle of their being and subsistence, even though they are separated.
It is further necessary to know that it is possible for natures to be united to each other hypostatically, as in the case of man, and that it is also possible for the hypostasis to assume an additional nature. Both of these are to be observed in Christ, because in Him the divine and human natures were united, while His animate body subsisted in the pre-existent hypostasis of God the Word and had this for a hypostasis. It is, however, quite impossible for one compound nature to be made from two natures or for one hypostasis to be made from two, because it is impossible for contrary essential differences to exist together in one nature. This is because it is of the very nature of these to distinguish from each other the natures in which they exist. And again, it is impossible for things that have once begun to subsist in themselves to have another principle of subsistence, for the hypostasis is subsistence in self. It must further be known that in the Holy Trinity a hypostasis is the timeless mode of each external existence.
One should know, moreover, that whenever a compound nature is produced, the parts must be coincident and a new thing made from other things. This new thing will not preserve the thing of which it has been composed as such, but will change and alter them. Thus, when the body has been made up from the four elements, a new thing has been made out of other things, and this new thing is neither pure fire nor any of the other elements, nor is it so called. It is the same with the mule, which is bred from a horse and an ass, for it is neither a horse nor an ass, nor it is so called. On the contrary, it is a new thing produced from others and which does not preserve unconfused and unchanged either one of those things of which it is composed.
[53] {Περὶ τῆς καθ' ὑπόστασιν ἑνώσεως.} Χρὴ γινώσκειν, ὅτι ἡ καθ' ὑπόστασιν ἕνωσις μίαν ὑπόστασιν τῶν ἑνουμένων ἀποτελεῖ σύνθετον σῴζουσα τὰς συνελθούσας πρὸς ἕνωσιν φύσεις καὶ τὴν τούτων διαφορὰν καὶ τὰ τούτων φυσικὰ ἰδιώματα ἀσύγχυτά τε καὶ ἄτρεπτα ἐν ἑαυτῇ. Αὕτη δὲ πρὸς ἑαυτὴν οὐδεμίαν ὑποστατικὴν ἔχει διαφοράν: αὐτῆς γὰρ γίνονται αἱ ἑκατέρου τῶν συνελθόντων πρὸς ἕνωσιν χαρακτηριστικαὶ διαφοραί, αἷς ἑκατέρων ἐκ τῶν ὁμοειδῶν χωρίζονται, ὡς ἐπὶ ψυχῆς ἔχει καὶ σώματος. Μία μὲν γὰρ ἐξ ἀμφοτέρων ἀποτελεῖται ἡ τοῦ Πέτρου τυχὸν ἢ τοῦ Παύλου ὑπόστασις σύνθετος, σῴζει δὲ ἐν ἑαυτῇ τὰς δύο τελείας φύσεις, τήν τε τῆς ψυχῆς καὶ τοῦ σώματος, καὶ τὴν τούτων διαφορὰν ἀσύμφυρτον καὶ τὰ τούτων φυσικὰ ἰδιώματα ἀσύγχυτα. Ἔχει δὲ ἐν ἑαυτῇ τὰ ἑκατέρας χαρακτηριστικὰ ἰδιώματα τά τε τῆς ψυχῆς τὰ χωρίζοντα αὐτὴν ἐκ τῶν λοιπῶν ψυχῶν καὶ τὰ τοῦ σώματος τὰ χωρίζοντα αὐτὸ ἐκ τῶν λοιπῶν σωμάτων, μηδαμῶς χωρίζοντα τὴν ψυχὴν ἐκ τοῦ σώματος ἀλλ' ἑνοῦντα καὶ συνάπτοντα, ἅμα δὲ τὴν ἐξ αὐτῶν συντεθειμένην μίαν ὑπόστασιν χωρίζοντα τῶν λοιπῶν ὁμοειδῶν ὑποστάσεων. Ἐπειδὰν δὲ ἅπαξ αἱ φύσεις τὴν πρὸς ἄλληλα καθ' ὑπόστασιν δέξωνται ἕνωσιν, ἀδιαίρετοι μένουσιν εἰς τὸ παντελές. Εἰ γὰρ καὶ χωρίζεται ἡ ψυχὴ τοῦ σώματος ἐν τῷ θανάτῳ, ἀλλ' ἡ ὑπόστασις ἀμφοτέρων μία καὶ ἡ αὐτή ἐστιν: ὑπόστασις γάρ ἐστιν ἡ ἐν τῇ ἀρχῇ τῆς ἑκάστου ὑπάρξεως κατ' αὐτὸ σύμπηξις. Μένει οὖν τό τε σῶμα καὶ ἡ ψυχή, ἀεὶ μίαν τὴν ἀρχὴν τῆς ἑαυτῶν ἔχοντα ὑπάρξεώς τε καὶ ὑποστάσεως, εἰ καὶ χωρισθῶσιν ἀλλήλων. Δεῖ δὲ γινώσκειν, ὅτι φύσεις μὲν ἑνωθῆναι ἀλλήλαις καθ' ὑπόστασιν ἐνδέχεται ὡς ἐπὶ τοῦ ἀνθρώπου καὶ φύσιν προσληφθῆναι ὑπὸ ὑποστάσεως καὶ ἐν αὑτῇ ὑποστῆναι δυνατόν, ἅπερ ἀμφότερα ἐπὶ τοῦ Χριστοῦ θεωροῦνται_καὶ γὰρ ἐν αὐτῷ καὶ αἱ φύσεις, ἡ θεία τε καὶ ἡ ἀνθρωπίνη, ἡνώθησαν, καὶ ἐν τῇ προϋπαρχούσῃ τοῦ θεοῦ λόγου ὑποστάσει ὑπέστη ἡ ἔμψυχος αὐτοῦ σὰρξ καὶ αὐτὴν ἔσχεν ὑπόστασιν, _ἐκ δύο δὲ φύσεων ἀποτελεσθῆναι μίαν φύσιν σύνθετον ἢ ἐκ δύο ὑποστάσεων μίαν ὑπόστασιν παντελῶς ἀδύνατον: διότι ἀδύνατον τὰς ἐναντίας οὐσιώδεις διαφορὰς ἐν μιᾷ φύσει συνυπάρξαι ἀλλήλαις: τούτων γὰρ ἔργον ἐστὶν ἀποδιιστᾶν ἀλλήλων τὰς φύσεις, ἐν αἷς ὑπάρξουσι. Καὶ πάλιν ἀδύνατον τὰ ἅπαξ καθ' ἑαυτὰ ὑποστάντα ἑτέραν ἀρχὴν ὑποστάσεως σχεῖν: ἡ γὰρ ὑπόστασις ἡ καθ' ἑαυτό ἐστιν ὕπαρξις. Ἰστέον δέ, ὡς ἐπὶ τῆς ἁγίας τριάδος ὑπόστασίς ἐστιν ὁ ἄναρχος τρόπος τῆς ἑκάστου ἀιδίου ὑπάρξεως. Χρὴ δὲ εἰδέναι, ὅτι, ἡνίκα σύνθετος γένηται φύσις, δεῖ ὁμόχρονα τὰ μέρη εἶναι καὶ ἐξ ἑτέρων ἕτερον ἀποτελεῖται μὴ φυλάττον ἀλλὰ τρέπον καὶ ἀλλοιοῦν τὰ ἐξ ὧν συνετέθη, ὡς ἐκ τῶν τεσσάρων στοιχείων ἀποτελουμένου τοῦ σώματος ἄλλο ἐξ ἄλλων γέγονε καὶ οὔτε πῦρ τέλειον οὔτε τι τῶν ἄλλων ἐστὶν ἢ λέγεται, καὶ ὡς ἐξ ἵππου καὶ ὄνου ἡμίονος: οὔτε γὰρ ἵππος οὔτε ὄνος ἐστὶν ἢ λέγεται ἀλλ' ἐξ ἑτέρων ἕτερον, μηδ' ὁπότερον τῶν, ἐξ ὧν συνετέθη, φυλάττον ἀσύγχυτόν τε καὶ ἄτρεπτον.