The doctrine that the pope can make a pronouncement, under special circumstances, on a matter of faith that must be definitively accepted by all the faithful. This is one of the most misunderstood concepts among Catholics and non-Catholics alike, and one whose exact meaning and exercise remain a matter of much debate within the church. The Catholic faith teaches that only God is infallible, and that God ensures that the church — rather than its members or leaders — will be free from error. A pope is not personally infallible. He is only able to make special declarations that are affirming a sacred truth that always existed. Papal infallibility was first formally defined in 1870, and it has only been invoked once since then – in 1950, when Pope Pius XII declared as dogma that the Virgin Mary was assumed body and soul into heaven at the end of her life. Pope Pius IX’s affirmation, in 1854, of the dogma of the Immaculate Conception (that the Virgin Mary was conceived without sin) is the only other instance in modern history in which papal infallibility has been invoked. Theologians continue to debate whether and what other teachings might be considered infallible.