EUTYCHIANS, ancient heretics, who denied the duplicity of natures in Christ; thus denominated from Eutyches, the archimandrite, or abbot of a monastery at Constantinople, who began to propagate his opinion A. D. 448. He did not, however, seem quite steady and consistent in his sentiments: for he appeared to allow of two natures, even before the union; which was apparently a consequence he drew from the principles of the Platonic philosophy, which supposes a pre-existence of souls: accordingly, he believed that the soul of Jesus Christ had been united to the divinity before the incarnation; but then he allowed no distinction of natures in Jesus Christ since his incarnation. This heresy was first condemned in a synod held at Constantinople by Flavian, in 448, approved by the council of Ephesus, called conventus latronum, in 449, and re-examined, and fulminated, in the general council of Chalcedon in 451. The legates of pope Leo, who assisted at it, maintained, that it was not enough to define, that there were two natures in Jesus Christ, but insisted strenuously, that, to remove all equivocations, they must add these terms, without being changed, or confounded, or divided.
The heresy of the Eutychians, which made a very great progress throughout the east, at length became divided into several branches. Nicephorus makes mention of no fewer than twelve: some called Schematics, or Apparentes, as only attributing to Jesus Christ a phantom or appearance of flesh, and no real flesh: others, Theodosians, from Theodosius bishop of Alexandria: others, Jacobites, from one James (Jacobus), of Syria; which branch established itself principally in Armenia, where it still subsists. Others were called Acephali, q. d. without head; and Severians, from a monk called Severus, who seized on the see of Antioch in 513. These last were subdivided into five factions, viz. Agnoites, who attributed some ignorance to Jesus Christ; the followers of Paul; Macarians, that is, the black Angelites, thus called from the place where they were assembled; and lastly, Adriates, and Cononites.