Summary of Doctrine on the Church
We also define that the holy apostolic see, and the Roman pontiff, holds the primacy
over the whole world, that the Roman pontiff is the successor of blessed Peter, prince of
the apostles, that he is the true vicar of Christ, the head of the whole Church and the
father and teacher of all Christians, and that to him was committed in blessed Peter the
full power of tending, ruling and governing the whole church, as is contained also in the
acts of ecumenical councils and in the sacred canons (COUNCIL OF FLORENCE, 1439).
Therefore, faithfully adhering to the tradition received from the beginning of the
christian faith, ... we teach and define as a divinely revealed dogma that when the Roman
Pontiff speaks ex cathedra, that is, when, in the exercise of his office as
shepherd and teacher of all Christians, in virtue of his supreme apostolic authority, he
defines a doctrine concerning faith or morals to be held by the whole Church, he
possesses, by the divine assistance promised to him in blessed Peter, that infallibility
which the divine Redeemer willed his Church to enjoy in defining doctrine concerning faith
or morals. Therefore, such definitions of the Roman Pontiff are of themselves, and not by
the consent of the Church, irreformable (VATICAN COUNCIL I, 1870).