The First Vatican Council decrees the dogma of papal infallibility.

The dogma of papal infallibility is a doctrine of the Roman Catholic Church that holds the pope is preserved from error when he solemnly proclaims a doctrine concerning faith or morals to be held by the entire Church. Contrary to a common misconception, the doctrine does not mean that the pope is always right or incapable of making mistakes in his personal opinions, administrative decisions, scientific views, or political judgments. Rather, it applies only under very specific conditions, known as speaking *ex cathedra* (“from the chair” of Saint Peter), when the pope exercises his supreme apostolic authority as the universal shepherd of the Church. Catholics believe that this protection from error is granted by the Holy Spirit to safeguard the integrity of Christian teaching.

The doctrine was formally defined at the First Vatican Council in 1870 through the constitution *Pastor Aeternus*. The council declared that the pope possesses infallibility only when, acting as the supreme pastor and teacher of all Christians, he defines a doctrine of faith or morals that is to be held by the whole Church. This definition built upon centuries of theological development and the longstanding belief that the Bishop of Rome, as the successor of Saint Peter, held a unique teaching authority within the Church. Supporters cited biblical passages such as Matthew 16:18–19 and Luke 22:32 as scriptural foundations for the doctrine, interpreting them as evidence of Christ’s special protection of Peter and his successors.

In practice, papal infallibility has been invoked very rarely. Most Catholic teachings are issued through the ordinary teaching authority, or Magisterium, rather than through formal *ex cathedra* declarations. The two most widely accepted examples of infallible papal definitions are Pope Pius IX’s proclamation of the dogma of the Immaculate Conception in 1854 and Pope Pius XII’s definition of the Assumption of the Virgin Mary in 1950. These declarations were made after extensive consultation with bishops around the world and were intended to clarify doctrines already widely held within the Church rather than introduce entirely new beliefs.

The dogma has been the subject of both theological support and criticism since its definition. Catholics regard it as an important safeguard that preserves the Church from doctrinal error on essential matters of faith and morals, reinforcing the unity of the worldwide Church. Critics, including many Protestant denominations and the Eastern Orthodox Church, reject the doctrine, arguing that it lacks sufficient biblical and historical support and grants excessive authority to the papacy. Even within Roman Catholicism, theologians emphasize that papal infallibility is an exceptional charism exercised under narrowly defined circumstances, making it far more limited than many people assume.