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Ex cathedra:
It is absolutely necessary for the salvation of every human creature to be subject to the Roman Pontiff.
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It's amazing how fiercely they promote him being a valid pope but constantly live as if he doesn't exist. This completely novel idea that one may resist and disobey everything a valid pope says so long as it's not an ex Cathedra statement. This is something straight out of the 20th century.

Pope Pius IX, Inter Multiplices: “This chair is the center of Catholic truth and unity, that is, the head, mother, and teacher of all the Churches to which all honor and obedience must be offered. Every church must agree with it because of its greater preeminence -- that is, those people who are in all respects faithful.”

Pope Pius IX, Neminem Vestrum: “In this way everybody will follow with due reverence, compliance, and obedience that full and supreme authority which our Lord Jesus Christ gave to Peter and to his successors, the popes: namely to feed, rule, and govern the universal Church…”

Pope Pius IX, Nostis et Nobiscuм: “Indeed one simple way to keep men professing Catholic truth is to maintain their communion with and obedience to the Roman Pontiff. For it is impossible for a man ever to reject any portion of the Catholic faith without abandoning the authority of the Roman Church. In this authority, the unalterable teaching office of this faith lives on. It was set up by the divine Redeemer and, consequently, the tradition from the Apostles has always been preserved.”

Pope Pius IX, Quanta Cura: “Nor can we pass over in silence the audacity of those who, not enduring sound doctrine, contend that "without sin and without any sacrifice of the Catholic profession assent and obedience may be refused to those judgments and decrees of the Apostolic See, whose object is declared to concern the Church's general good and her rights and discipline, so only it does not touch the dogmata of faith and morals." But no one can be found not clearly and distinctly to see and understand how grievously this is opposed to the Catholic dogma of the full power given from God by Christ our Lord Himself to the Roman Pontiff of feeding, ruling and guiding the Universal Church.”

Pope Pius IX, Quartas Supra: “For the Catholic Church has always regarded as schismatic those who obstinately oppose the lawful prelates of the Church and in particular, the chief shepherd of all. Schismatics avoid carrying out their orders and even deny their very rank. Since the faction from Armenia is like this, they are schismatics even if they had not yet been condemned as such by Apostolic authority. For the Church consists of the people in union with the priest, and the flock following its shepherd.[24] Consequently the bishop is in the Church and the Church in the bishop, and whoever is not with the bishop is not in the Church. Further more, as Our predecessor Pius VI warned in his Apostolic letter condemning the civil constitution of the clergy in France,[25] discipline is often closely related to doctrine and has a great influence in preserving its purity. In fact, in many instances, the holy Councils have unhesitatingly cut off from the Church by their anathema those who have infringed its discipline.” “13. But the neo-schismatics have gone further, since "every schism fabricates a heresy for itself to justify its withdrawal from the Church."[26] Indeed they have even accused this Apostolic See as well, as if We had exceeded the limits of Our power in commanding that certain points of discipline were to be observed in the Patriarchate of Armenia. Nor can the Eastern Churches preserve communion and unity of faith with Us without being subject to the Apostolic power in matters of discipline. Teaching of this kind is heretical, and not just since the definition of the power and nature of the papal primacy was determined by the ecuмenical Vatican Council: the Catholic Church has always considered it such and abhorred it.”