Immaculate Conception: Main article: Immaculate Conception Since the Middle Ages, Roman Catholic theologians had argued the question of whether or not Mary had been subject to original sin. In general, the Franciscans argued in favor of her "immaculate conception", the doctrine that she, from the moment of her conception, had been preserved by God from all sin and all tendency to sin; the Dominicans, on the other hand, including most notably Thomas Aquinas, argued that Mary's sinlessness is a grace granted to her at some time after her conception. In 1854, Pope Pius IX effectively ended the debate for Roman Catholics by proclaiming the dogma of the "Immaculate Conception", stating that "the Blessed Virgin Mary in the first instant of her conception was preserved exempt from all stain of original sin by a singular privilege and grace granted by God (cf. Luke 1:28), in view of the merits of Jesus Christ, the Saviour of the human race." ("Ineffabilis Deus", issued on 8 December 1854). It was subsequently claimed that the Blessed Virgin Mary during her sixteenth appearance in Lourdes on March 25, 1858 announced to Bernadette Soubirous "I am the Immaculate Conception". The term Immaculate Conception is also widely used within Roman Catholicism to refer to the Virgin Mary.