What is papal infallibility?
The short answer
Papal infallibility means that when the Pope, as supreme teacher of the whole Church, solemnly defines a doctrine of faith or morals to be held by all believers, the Holy Spirit protects that definition from error. It does not mean the Pope is sinless or that everything he says is infallible.
What it is
The First Vatican Council (1870) defined that the Roman Pontiff is infallible "when he speaks ex cathedra" — that is, when, as pastor and teacher of all Christians, he defines with his supreme apostolic authority a doctrine concerning faith or morals to be held by the whole Church (CCC 891).
What it is not
- Not impeccability. Popes can and do sin; they go to confession.
- Not every statement. Interviews, homilies, opinions and prudential decisions are not infallible.
- Not new revelation. The Pope cannot invent doctrine; he can only define what belongs to the deposit of faith handed down from the apostles (CCC 891).
- Not science, politics or history as such — only faith and morals.
How often has it been used?
Rarely. The two clearest ex cathedra definitions are the Immaculate Conception (1854) and the Assumption of Mary (1950).
Why would Christ give this gift?
Jesus prayed for Peter "that your own faith may not fail… strengthen your brothers" (Luke 22:32), and entrusted him with the keys of the kingdom (Matthew 16:19). A Church sent to teach all nations needs a way to settle disputed questions with certainty. Infallibility is the Spirit's protection of the Church's faith, not a personal superpower.
Ordinary and extraordinary teaching
The Church's teaching office — the Magisterium — is also infallible when all the bishops in communion with the Pope, teaching throughout the world, agree that a matter of faith or morals must be held definitively (CCC 892, 2035). Other teachings, not proposed definitively, still call for "religious assent" of mind and will.