9th–11th centuries (1054)

The East–West schism as a dispute over the nature of the Church and the primacy of Peter

Pelikan argues that from the 9th to the 11th century the schism itself became the chief doctrinal problem, and in the "Photian schism" differences ranging from Trinitarian doctrine to the nature of the Church erupted into open conflict. Latin exegesis (Nicholas I) saw in the words "You are Peter" (Matt. 16:18) an affirmation of the primacy of the Roman see, while Greek theologians took the rock to be Peter's confession and ascribed the power of the keys to all faithful bishops; in Pelikan's formula, for the East the pope is first because he is orthodox, for the West he is orthodox because he is first. Photius declared the papal claims groundless in his treatise Against the Primacy. On 16 July 1054 the legate Humbert laid on the altar of Hagia Sophia the excommunication of Michael Cerularius, and Cerularius' council condemned the West.