In Roman Catholicism , the dogma that Mary was not tainted by original sin .
Early exponents included St. Justin Martyr and St. Irenaeus ; St. Bonaventure and St. Thomas Aquinas were among those who opposed it. In 1439 the Council of Basel stated that the belief was in accordance with Catholic faith, and in 1709 Pope Clement XI made the feast of the Immaculate Conception a holy day of obligation. In 1854 Pius IX issued a papal bull making it official church dogma. See also Virgin Birth .