1854

The dogma of the Immaculate Conception (the bull Ineffabilis Deus)

The question of Mary's immaculate conception had divided theologians for centuries. Franciscans, following Duns Scotus, taught immaculate conception; Dominicans, following Aquinas, taught sanctification before birth. In 1483 Sixtus IV declared the question open.

After polling bishops in 1849, Pope Pius IX in 1854 proclaimed a dogma by the bull Ineffabilis Deus. It declared that Mary, by a special grace of God, was preserved from all sin, including original sin, from the moment of her conception.

The bull was accepted with almost no controversy. It was the first time in history a pope alone, without convening a council, defined a dogma of faith. This prepared the ground for the proclamation of papal infallibility at the First Vatican Council.