"saying they are "many men," is a customary abuse of language"

 We say, then, to begin with, that the practice of calling those who are not divided in nature by the very name of their common nature in the plural, and saying they are many men, is a customary abuse of language, and that it would be much the same thing to say they are many human natures. And the truth of this we may see from the following instance. When we address any one, we do not call him by the name of his nature, in order that no confusion may result from the community of the name, as would happen if every one of those who hear it were to think that he himself was the person addressed, because the call is made not by the proper appellation but by the common name of their nature: but we separate him from the multitude by using that name which belongs to him as his own — that, I mean, which signifies the particular subject. Thus there are many who have shared in the nature — many disciples, say, or apostles, or martyrs— but the man in them all is one; since, as has been said, the term man does not belong to the nature of the individual as such, but to that which is common. For Luke is a man, or Stephen is a man; but it does not follow that if any one is a man he is therefore Luke or Stephen: but the idea of the persons admits of that separation which is made by the peculiar attributes considered in each severally, and when they are combined is presented to us by means of number; yet their nature is one, at union in itself, and an absolutely indivisible unit, not capable of increase by addition or of diminution by subtraction, but in its essence being and continually remaining one, inseparable even though it appear in plurality, continuous, complete, and not divided with the individuals who participate in it.

 Φαμὲν τοίνυν πρῶτον μὲν κατάχρησίν τινα συνηθείας εἶναι τὸ τοὺς μὴ
διῃρημένους τῇ φύσει κατ' αὐτὸ τὸ τῆς φύ σεως ὄνομα πληθυντικῶς ὀνομάζειν καὶ λέγειν ὅτι πολλοὶ ἄνθρωποι, ὅπερ ὅμοιόν ἐστι τῷ λέγειν ὅτι πολλαὶ φύσεις
ἀνθρώπιναι. καὶ ὅτι ταῦτα οὕτως ἔχει, δῆλον ἂν ἡμῖν ἐντεῦθεν γένοιτο·
προσκαλούμενοι γάρ τινα, οὐκ ἐκ τῆς φύσεως αὐτὸν ὀνομάζομεν, ὡς ἂν μή τινα
πλάνην ἡ κοινότης τοῦ ὀνόματος ἐμποιήσειεν, ἑκάστου τῶν ἀκουόντων ἑαυτὸν
εἶναι τὸν προσκληθέντα νομίζοντος, ὅτι μὴ τῇ ἰδιαζούσῃ προση γορίᾳ ἀλλ' ἐκ τοῦ
κοινοῦ τῆς φύσεως ὀνόματος ἡ κλῆσις γίνεται· ἀλλὰ τὴν ἰδίως ἐπικειμένην αὐτῷ
(τὴν σημαντικὴν λέγω τοῦ ὑποκειμένου) φωνὴν εἰπόντες, οὕτως αὐτὸν τῶν πολλῶν ἀποκρίνομεν, ὥστε πολλοὺς μὲν εἶναι τοὺς μετεσχη κότας τῆς φύσεως, φέρε εἰπεῖν μαθητὰς ἢ ἀποστόλους ἢ μάρτυρας, ἕνα δὲ ἐν πᾶσι τὸν ἄνθρωπον, εἴπερ, καθὼς εἴρηται, οὐχὶ τοῦ καθ' ἕκαστον, ἀλλὰ τοῦ κοινοῦ τῆς φύσεώς ἐστιν ὁ ἄνθρωπος· ἄνθρωπος γὰρ ὁ Λουκᾶς ἢ ὁ Στέφανος, οὐ μήν, εἴ τις ἄνθρωπος, πάντως καὶ Λουκᾶς ἐστιν ἢ Στέφανος. Ἀλλ' ὁ μὲν τῶν ὑποστάσεων λόγος διὰ τὰς ἐνθεωρουμένας 3,1.41 ἰδιότητας ἑκάστῳ τὸν διαμερισμὸν ἐπιδέχεται καὶ κατὰ σύν θεσιν ἐν ἀριθμῷ θεωρεῖται· ἡ δὲ φύσις μία ἐστίν, αὐτὴ πρὸς ἑαυτὴν ἡνωμένη καὶ ἀδιάτμητος ἀκριβῶς μονάς, οὐκ αὐ ξανομένη διὰ προσθήκης, οὐ μειουμένη δι' ὑφαιρέσεως, ἀλλ' ὅπερ ἐστὶν ἓν οὖσα καὶ ἓν διαμένουσα κἂν ἐν πλήθει φαίνηται, ἄσχιστος καὶ συνεχὴς καὶ ὁλόκληρος καὶ τοῖς μετέχουσιν αὐτῆς τοῖς καθ' ἕκαστον οὐ συνδιαιρουμένη. (Ad Ablabium 3.1.39-40)