Mary is the clearest case in Christianity of devotion running ahead of definition and definition running to catch up. Theotokos, God-bearer, was hammered out at Ephesus in 431 in an argument about Christ, not about her: if Mary bore only the human part, then the union is not real. Every mainstream branch accepts it, including the Reformers. After that the roads fork. Perpetual virginity was standard until the modern period, held by Luther, Calvin and Wesley, and quietly dropped by most later Protestants. The Immaculate Conception, which concerns Mary's own conception free of original sin, was defined by Pius IX in 1854 and is rejected by the Orthodox, partly because they do not hold the Augustinian doctrine it presupposes. The Assumption was defined in 1950; the East keeps the feast of the Dormition on the same day and declines to dogmatise it. In practice the intensity of Marian devotion in Mexico, the Philippines, Poland, southern Italy and Kerala is a far bigger fact about world Christianity than any of these definitions.