Is the infallibility of the Pope applicable in all cases, or is it restricted to certain domains?
The Pope is, indeed, in his capacity as the visible head of the Church:
The supreme teacher of God's revealed truth;
The supreme priest;
The supreme legislator in ecclesiastical affairs;
The supreme judge in ecclesiastical causes, in causis ecclesiasticis.
However, according to the very clear text of the definition from the First Vatican Council, he possesses the gift of infallibility only in the exercise of his office as supreme "Teacher," instructing in the truth necessary for salvation, revealed by God; and not in his role as supreme priest, nor as supreme legislator in matters of discipline, nor as supreme judge in ecclesiastical causes, nor in the other functions to which his office as head of the Church may extend.
When I do not include ecclesiastical causes or trials here in the domain of papal infallibility, I understand by this expression the cases that ordinarily come before ecclesiastical tribunals, such as matrimonial cases, benefices, patronage rights, etc.
But points in dispute concerning faith, the Pope decides, naturally, in his capacity as supreme teacher.
– Since the doctrinal definitions of the Church encompass both dogma and morals, it can perfectly happen, according to the nature of things, that decisions concerning morals are also addressed by the Pope to the universal Church in the form of orders or prohibitions (praecepta morum).
– One will understand all these things better if one compares this chapter of the Council's constitution with the preceding chapter, where it is expressly stated that the Pope possesses the full and supreme power of jurisdiction over the entire Church, "not only in matters that pertain to faith and morals, but also in those that belong to the discipline and government of the Church spread throughout the world."
From this, it is seen that there are four principal classes of objects within the ecclesiastical domain that are subject to the supreme power of the Pope, namely:
That which pertains to faith,
That which pertains to morals,
That which pertains to discipline,
That which pertains to the government of the Church.
In all these matters, it is the duty of all to obey the Pope sincerely.
The fourth chapter (Bishop Joseph Fessler's "The True and False Infallibility of the Popes"), entitled "On the Infallible Magisterium of the Roman Pontiff," then deals, from the perspective of the Pope's teaching authority, with the objects of the first and second classes (faith and morals), leaving aside those of the third and fourth (discipline and the government of the Church).
And it is solely concerning the Pope's decisions touching faith and morals that it is declared as a dogma revealed by God that these decisions, thanks to the divine assistance promised to the Pope in the person of Saint Peter, possess a character of certainty immune from all error, in other words, infallible.
This infallibility, granted to the Pope in the exercise of his office as pastor and teacher of all Christians, is further designated, for greater precision, as "that infallibility with which the divine Redeemer willed His Church to be endowed in defining doctrine concerning faith or morals."
If, therefore, one asks what is the extent of the Pope's infallibility even in matters of faith and morals, it is first necessary to investigate what is the extent of the Church's infallibility in these matters.
Without entering into an examination of this very vast question, which is treated in detail in major theological works, I will content myself with citing the following proposition long admitted in theology: Even in dogmatic decrees, dogmatic bulls, etc., one must not regard everything found therein indiscriminately as a dogmatic decision, and consequently as an object of infallibility: in particular, one must not consider as such that which is mentioned only in passing or that which serves merely as an introduction or as supporting reasoning.
Finally, the Council adds further that the decisions of the Pope, in which, in his capacity as pastor and teacher of all Christians and by virtue of his supreme apostolic authority, he formulates a doctrine concerning faith or morals as to be held by the entire Church, "are irreformable of themselves, and not from the consent of the Church."
This certainly does not mean in any way that the Pope can never decide something contrary to the tradition of the Church or that he can never stand alone in opposition to all the other Bishops; but only that the infallibility of his doctrinal decisions does not depend on the consent of the Church, but rather on the divine assistance which was specially granted to him in the person of Saint Peter for the exercise of his office as supreme teacher.
Also read | Who was the Catholic mystic Mother Eugenia Ravasio?
And since it is expressly stated, concerning the decisions to which the infallibility of the pontifical magisterium pertains, that they are "irreformable of themselves," it follows that the laws which the Pope publishes regarding disciplinary matters, which are subject to change, are not included, precisely because of this character of mutability, in the definition of faith of the First Vatican Council.
Source: Bishop Joseph Fessler – The True and False Infallibility of the Popes – 1877