No Pope can ever teach heresy. No Pope can ever commit apostasy, heresy, or schism. Those who accuse any current Roman Pontiff of teaching heresy, or of committing apostasy, heresy, or schism, are themselves guilty of schism. For “it arises from the necessity of salvation that all the faithful of Christ are to be subject to the Roman Pontiff.” [Fifth Lateran Council]
A Pope can err in his personal opinions. A faithful Catholic can respectfully disagree with the personal opinion of a Pope.
A Pope can err in his decisions on discipline. A faithful Catholic can respectfully disagree with a decision the Pope has made on discipline. But he is subject to that decision, nonetheless. And an error on discipline is not tantamount to heresy.
A Pope can also err, to a limited extent, in his non-infallible teachings. The faithful are generally required to give ordinary assent (religious submission of will and intellect) to the non-infallible teachings of the Magisterium, including the Papal Magisterium. But some faithful dissent is permissible (licit theological dissent).
A Pope cannot err when he is exercising the infallible teaching authority of the Magisterium, in Papal Infallibility, Conciliar Infallibility, or by his participation in the ordinary and universal Magisterium.
Cardinals have the role to assist the Pope, and to be taught and corrected by him. The Cardinals do not have any role or authority to teach or correct the Pope. They cannot issue a formal correction, if they think that a Pope has erred.
And no one, from the Cardinals to the least of the laity, is justified in assuming that the Pope must be wrong, merely because his words or deeds are contrary to their own personal understanding. Your understanding of infallible Sacred Scripture and infallible Sacred Tradition is fallible; you may have misunderstood those infallible sources. And the same is true for your understanding of past or present magisterial teachings.
A schism draws near. We will have to wait and see which Cardinals and Bishops depart in the schism, and which remain faithful. But several Cardinals have already risen up to publicly oppose Pope Francis. They speak as if their understanding of Tradition, Scripture, Magisterium could not err. They speak as if they have the role to teach and correct the Pope, and as if he has no such role over them.
Their request for “clarification” of Amoris Laetitia is not spoken, as far as I can tell, with the attitude of students seeking to learn, but with the attitude of teachers seeking to correct. And if the Pope does not speak and act as they wish, it seems that they will continue to oppose him.
There may or may not be errors in the non-infallible teachings of Amoris Laetitia. But the Cardinals lack the authority to correct the Pope, and no Pope can teach or commit heresy.
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