Papal infallibility
Papal infallibility is a dogma of the Roman Catholic Church which states that, in virtue of the promise of Jesus to Peter, the pope when appealing to his highest authority is preserved from the possibility of error on doctrine "initially given to the apostolic Church and handed down in Scripture and tradition". This doctrine was defined dogmatically at the First Vatican Council of 1869–1870 in the document "Pastor aeternus", but had been defended before that, existing already in medieval theology and being the majority opinion at the time of the Counter-Reformation.