Pastor aeternus

The primacy of the Bishop of Rome over the whole Catholic Church is derived from the pope's status as successor to Peter as "Prince of the Apostles" and as "Vicar of Christ" (Vicarius Christi).

This Holy See has always maintained this, the constant custom of the Church demonstrates it, and the ecumenical councils, particularly those in which East and West met in the union of faith and charity, have declared it.

Ex cathedra means literally "from the chair”; it is a theological term which signifies authoritative teaching and is more particularly applied to the definitions given by the Roman pontiff.

In the conclusion of the fourth chapter of Pastor aeternus, the council declared the following:[7]...We teach and define that it is a dogma divinely revealed that the Roman pontiff when he speaks ex cathedra, that is when in discharge of the office of pastor and doctor of all Christians, by virtue of his supreme Apostolic authority, he defines a doctrine regarding faith or morals to be held by the universal Church, by the Divine assistance promised to him in blessed Peter, is possessed of that infallibility with which the divine Redeemer willed that his Church should be endowed in defining doctrine regarding faith or morals, and that therefore such definitions of the Roman pontiff are of themselves, and not from the consent of the Church, irreformable.

The Catholic priest August Bernhard Hasler [de] wrote a detailed criticism of the First Vatican Council, presenting the passage of the infallibility definition as orchestrated.

[9] Mark E. Powell, in his examination of the topic from a Protestant point of view, writes: "August Hasler portrays Pius IX as an uneducated, abusive megalomaniac, and Vatican I as a council that was not free.