These six points contain the whole definition of Infallibility. I will therefore take them in order, and then answer certain objections.
I. First, the definition limits the infallibility of the Pontiff to the acts which emanate from him ex cathedra. This phrase, which has been long and commonly used by theologians, has now, for the first time, been adopted into the terminology of the Church; and in adopting it the Vatican Council fixes its meaning. The Pontiff speaks ex cathedra when, and only when, he speaks as the Pastor and Doctor of all Christians. By this, all acts of the Pontiff as a private person, or a private doctor, or as a local Bishop, or as sovereign of a state, are excluded. In all these acts the Pontiff may be subject to error. In one and one only capacity he is exempt from error; that is, when, as teacher of the whole Church, he teaches the whole Church in things of faith and morals.
Our Lord declared, 'Super cathedram Moysi sederunt scribæ et Pharisæi:' the scribes and Pharisees sit in the chair of Moses. The seat or 'cathedra' of Moses signifies the authority and the doctrine of Moses; the cathedra Petri is in like manner the authority and doctrine of Peter. The former was binding by Divine command and under pain of sin, upon the people of God under the old law; the latter is binding by Divine command and under pain of sin, upon the people of God under the new.
I need not here draw out the traditional use of the term cathedra Petri, which in St. Cyprian, St. Optatus, and St. Augustine is employed as synonymous with the successor of Peter, and is used to
