When the Antiochene priest Nestorius was elected bishop of Constantinople 428, the Antiochene and Alexandrian Christologies had for some decades been confronting each other from very distant positions: the one gave significance and autonomy to Christ’s human nature to the point of de facto predicating two subjects in him, compromising his unity; the other ensured his unity by making the Logos the sole subject, with the result of reducing the humanity to a passive instrument of the Logos.
Nestorius continued Theodore’s formula predicating a single prosopon in Christ, but in fact he held the two natures so distinct as to not admit the communicatio idiomatum affirmed by Origen: hence his aversion to the title Mother of God Theotokos, traditionally given to Mary, and preference for the title Mother of Christ Christotokos.
Moscow Map Tourist Attractions Cyril considered the union of natures in Christ according to prosopon too weak and extrinsic, and substituted for it a union according to hypostasis, a much stronger term to indicate the unity of the subject; he spoke of a unity of nature in Christ and adopted the formula one single nature of the incarnate Logos, claiming that we can speak of two natures in Christ only before the union, i.e., only in theory, because the union produced a single nature, corresponding to a single hypostasis, i.e., a single subject and center of will and activity.
In this single nature resulting from the union, Cyril kept the properties of the divinity and of the humanity very distinct, but this was not enough to make his formulations acceptable to the Antiochenes, who considered them Apollinarist in tone. In fact the pact of union of 433, which reconciled Cyril with the Antiochenes after the condemnation of Nestorius at Ephesus in 431, was just a compromise, to which Cyril submitted only for political reasons, sacrificing the most characteristic points of his doctrine: the formula affirmed the union in Christ of two natures, without confusion, in a single prosopon, and defined Mary as Mother of God.