The Doctrine of Papal Infallibility

Papal infallibility is the tenet that when a pope speaks with the full authority of his office (ex cathedra) on a matter of faith or morals, he teaches infallibly. Although instances of it are rare in the past 2,000 years, it is one of the most distinctive and least understood dogmas of the Roman Catholic Church, even among its members. It is also a divisive point between Catholics and other Christians, one viewed as an obstacle to ecumenical dialogue. 

Papal infallibility was defined—not without controversy—by the First Vatican Council in 1870. As with so many beliefs in Christianity, however, its origins are centuries old, going back to at least the medieval period, and arguably earlier. John Freymann, permanent military professor in history at the U.S. Naval Academy, traces the origins and development of papal infallibility, placing it an historical context and drawing out its theological implications.