A fifth-century Christian heresy that held there were two distinct persons in the Incarnate Christ, one human and the other divine, as against the orthodox teaching that Christ was a divine person who assumed a human nature. Its name was taken from Nestorius (died c. 451), a native of Germanicia in Syria, and later Bishop of Constantinople. Nestorianism was condemned by the ecumenical Council of Ephesus in 431.
Postulating two separate persons in Christ, when Nestorius came to describe their union, he could not have them joined ontologically (in their being) or hypostatically (constituting one person), but only morally or psychologically. They would be united only by a perfect agreement of two wills in Christ, and by a harmonious communication of their respective activities. This harmony of wills (eudoxia) and the communion of action to which it gives rise are what forms the composite personality (henosia) of Christ.
In the Nestorian system we cannot speak of a true communication of idioms, i.e., that while the two natures of Christ are distinct the attributes of one may be predicated of the other in view of their union in the one person of Christ. Accordingly it could not be said that God was born, that he was crucified or died; Mary is not the Mother of God, except in the broad sense of giving birth to a man whose human personality was conjoined to the Word of God.
Nestorian bishops continued to propagate their views, and the confusion this produced among the people contributed to the success of Islam in the seventh century.