This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
The word at stake was Theotokos, God bearer, a title already in wide devotional use for Mary before Nestorius objected to it. His argument was not that Mary was unimportant but that calling her God bearer risked collapsing the distinction between Christ divine and human sides, as though God himself had a beginning in her womb. He proposed Christotokos, Christ bearer, as the more careful term.
Cyril of Alexandria, and the wider devotional habit Nestorius was pushing against, heard something else in the proposal: two subjects loosely cooperating rather than one person who is genuinely God and genuinely man. The Council of Ephesus in 431, convened in circumstances that were as much about ecclesiastical rivalry between Alexandria and Constantinople as about the theology itself, condemned Nestorius before the bishops loyal to him had even arrived, and deposed him.
What exactly Nestorius held is harder to settle than the council record suggests. His own later defense, the Bazaar of Heracleides, written from exile, reads to many modern scholars as compatible with a genuine union of natures, closer to what Chalcedon would define twenty years later than to the two person Christology his name came to label. The Church of the East, which did not accept Ephesus authority, maintains today that it was never Nestorian in the condemned sense, and its 1994 joint declaration with Rome treated the historic dispute as substantially a matter of language rather than of the faith itself.