In Christian theology, infallibility is the doctrine that in matters of faith and morals the church, both in teaching and in believing, is protected from serious error by "divine dispensation." This doctrine is most associated with the Catholic church, but is also applied by the Orthodox church to ecumenical councils. The doctrine is widely rejected by Protestants on the grounds that only God can be described as infallible.
Catholic theology asserts that the entire church is infallible (and therefore cannot err in matters of faith) when, from bishops to laity, it shows universal agreement in matters of faith and morals. Evidently popularity produces truth. Only a few persons in the church (those who hold its highest teaching office) are believed to proclaim Christian doctrine infallibly: (1) the entire body of bishops in union with the pope when it teaches with moral unanimity; (2) an ecumenical council which receives papal approval; and (3) under certain conditions, the pope alone.
What is Papal Infallibility?
Papal Infallibility, also called ultramontanism, is limited to when the Pope is speaking ex cathedra, that is when he is speaking in his official capacity as the "pastor and teacher" of all Christians in defining matters of morals and faith.
Vatican I, Pope Pius IX, and Papal Infallibility
How did Pius IX manage to get papal infallibility declared an official dogma? Catholic theologian Hans Küng, critical of this dogma, argues for four principle reasons: "Pius IX had a sense of divine mission which he carried to extremes; he engaged in double dealing; he was mentally disturbed; and he misused his office."
Criticisms of Papal Infallibility
There have been many Catholic critics of the doctrine of papal infallibility. In 1979 Father August Bernhard Hasler, Catholic priest, historian, and former staff member of the Vatican's Secretariat for Christian Unity, published "How the Pope became Infallible: Pius IX and the Politics of Persuasion." His description largely matches that of Hans Küng but differs greatly from the official version of the Church. Since he used Vatican documents which still haven't been released to the public, we should seriously consider his charges...