Eutychianism the name of a doctrinal system called after Eutyches, according to which there was in Christ only one nature, that of the incarnate Word, his human nature having been absorbed in a manner by his divine nature. Eutyches, like Cyril, laid chief stress on the divine in Christ, and denied that two natures could be spoken of after the incarnation. In our Lord, after his birth, he worshipped only one nature, the nature of God become flesh and man: μίαν φύσιν προσκυνεῖν, καὶ ταύτην Θεοῦ σαρκωθέντος καὶ ἐνανθρωπἠσαντος, or, as he declared before the synod at Constantinople, ῾Ομολογῶ ἐκ δύο φύσεων γεγεννῆσθαι τὸν κύριον ἡμῶν πρὸ τῆς ἑνήσεως· μετὰ δὲ τὴν ἕνωσιν μίαν φύσιν ὁμολογῶ (Mansi, 6:744). In behalf of his view he appealed to the Scriptures, to Athanasius and Cyril, and to the Council of Ephesus in 431. The impersonal human nature is assimilated, and, as it were, deified by the personal Logos, so that his body is by no means of the same substance (ὁμοούσιον) with ours, but a divine body. All human attributes are transferred to the one subject, the humanized Logos. Hence it may and must be said, God is born, God suffered, God was crucified and died. He asserted, therefore, on the one hand, the capability of suffering and death in the Logos-personality, and, on the other hand, the deification of the human in Christ. The other side imputed to Eutychianism the doctrine of a heavenly body, or of an apparent body, or of the transformation of the Logos into flesh. So Theodoret (Fab. haer. 4:13). Eutyches said Christ had a σῶμα ἀνθρώπου, but not a σῶμα ἀνθρώπινον and he denied the consubstantiality of his acrop with ours. Yet he expressly guarded himself against Docetism, and against all speculation: Φυσιολογεῖν ἐμαυτῷ οὐκ ἐπιτρέπω. He was really neither a philosopher nor a theologian, but only insisted on some theological opinions and points of doctrine with great tenacity and obstinacy" (Schaff, History of the Christian Church, 3:737 sq.).
Bishop Forbes cites Photius and Johannes Damascenus aptly on Eutychianism as follows, viz.: "If there be one nature in Christ, it is either the divine or the human nature; if it be only the divine nature, where is the human? and if there be only the human, you cannot escape from denying the divine. But if it be something different from these (for this is the only other alternative they have, and they seem to lean that way), how shall not in that case Christ be of a different nature, both from his Father and from us? Can anything be more impious or absurd to say that the Word of God, who is God, became man, to the corruption of his own deity, and to the annihilation of the humanity he assumed? For this absolutely follows with those who have dared to speak of Christ as of neither nature, but of one besides these" (Photius, Epist. 1, cont. Eutych. cit. Suicer). "The two natures were without conversion or alteration joined together, and the divine nature did not depart from its own simplicity, nor did the nature of man turn into the nature of God, nor was it deprived of existence, nor was one composite nature made out of two; for a composite nature cannot be consubstantial with either of those natures from whence it is compounded. If, therefore, according to the heretics, Christ exist in one compounded nature after the union, he is changed from a simple into a compounded nature, and is not consubstantial with his Father, who is of a simple nature, nor with his mother, for she is not made up of the Godhead and manhood. And he will be neither in the Godhead nor in the manhood, nor will he be called God or man, but Christ only; and Christ will be the name not of his person, but of his own nature, as they deem. But we do not hold Christ to be of a composite nature, as the body and soul make the man, but we believe and confess that he is of the Godhead and manhood; perfect God and perfect man from and in two natures. Were he of one nature, the same nature would be at once created and increate, simple and composite, mortal and immortal. And the union of two natures in Jesus Christ has taken place neither by disorder (φυομός) nor by mixture (syncrasis or anacrasis), as Eutyches, Dioscorus (of Alexandria), and Severus say; neither is it personal (προσωπικόν) nor relative, nor κατ' ἀξίαν, nor from identity of will, nor from equality of honor, nor from the same name, as Nestorius, Diodorus (of Tarsus), and Theodorus (of Mopsuestia) said; but by synthesis; or personally (καθ᾿ ὐπόστασιν), immutably, inconfusedly, unalterably, inherently, inseparably, in two perfect natures in one person. And we term this union essential (ούσιώδη), that is, true and not fantastic; essential, not in that one nature is made of the two, but that they are mutually united in truth into one composite person of the Son of God. And their substantial differences are preserved, for that which is created remains created, and that which is increate remains increate; the mortal remains mortal, the immortal abides immortal. The one shines forth in miracles, the other submits to injuries; and the Word appropriates to itself that which is of man, For its are the things that pertain to the Sacred Flesh, and it gives its own properties to the flesh, .according to the law of the communication of properties and the unity of person, for he is the same who performs both the God-like and the manlike actions in either form with the communion of the other. Wherefore the Lord of glory is said to be crucified, although the divine nature did not suffer, and the Son of man, even before his passion, is confessed to be in heaven, as the Lord himself said (John 3). For there is one and the same Lord of glory, who is naturally and in truth the Son of man, that is, made man. We acknowledge both his miracles and his sufferings, though the first were performed according to one nature, the latter endured according to the other. Thus we know that his one person and his two natures are preserved. By the difference of the natures he is, on the one hand, one with the Father and the Holy Ghost; on the other hand, he is one with his mother and with us. And these two natures are joined in one composite person, in which he differs as from the Father and the Holy Ghost, so from his mother and us also" (Joh. Damascenus, Fid. Orth. 3:3, abr.). Bishop Forbes adds: "Now we have all a great tendency to Eutychianism. It gets over a great difficulty in the reception of truth to believe the humanity of our Lord destroyed. For faith now requires of us to believe that the human body of Jesus Christ still is, and that to it the Word is hypostatically joined, and that beyond the spheres and systems of which we are cognizant, it, partaking of our nature, is at the right hand of God" (On the Nicene Creed, Oxford, 1852, page 201 sq.).
The Council of Chalcedon (A.D. 451) adopted the doctrine stated by pope Leo in his letter to Flavianus, SEE LEO, viz. in substance, "that in Christ two distinct natures were united in one person, without any change, mixture, or confusion." The Creed of Chalcedon states that "the one Son of God, our Lord Jesus Christ, is of one substance with the Father according to the Godhead, and of one substance with us according to the manhood — like to us in all things except sin; one and the same Christ, Son, Lord, Only-begotten, in two natures, without confusion, without conversion, without division, without separation — the difference of the natures not being taken away by reason of the unity, but the propriety of each being preserved and joined together to form one person." The creed of the council was not by any means universally received in the East. But the name Eutychianism gave way to that of Monophysitism. The ecclesiastical organizations adhering to the heresy are commonly known by the names of Jacobites, Armenian Church, Copts, and Abyssinian Church (see the special articles on these churches). For a sketch of the fortunes of the theory known as Eutychianism, SEE MONOPHYSITES. SEE CHALCEDON; SEE CHRISTOLOGY; SEE EUTTYCHES; SEE DIOSCUROS; and consult Pearson, On the Creed (Oxford, 1820), 2:179 sq.; Schaff, Ch. History, 1.c.; Waterland, Works (Oxford), 3:115, 411; Hefele, Conciliengeschichte, 2:249 et al.; Baur, Dogmengeschichte, 1:2, 256 sq.; Cunningham, Historical Theology, chapter 10, § 1.