I want to make some comments on a topic that has been much discussed in Church history among Catholic theologians: the question of in what ways a Pope might be able to believe or teach error or even heresy, and what the Church should do about it if that should happen.
Let me start with a selection from St. Francis de Sales, who I think lays out the prevailing view on this subject that has been mostly followed by theologians throughout the history of the discussion of this topic. St. Francis is one of the Church's great theologians, a Doctor of the Church. He is writing towards the end of the sixteenth century, responding to the positions and arguments of the Protestant Reformation. My text is taken from the full and plain text version of The Catholic Controversy as found here on the Internet Archive website. This version was published originally in 1909 (Third Edition, Revised and Augmented) in London by Burns and Oates, translated by Rev. H. B. Mackey, under the direction of Rev. John Cuthbert Hedley, Bishop of Newport.
Under the ancient law the High Priest did not wear the Rational except when he was vested in the pontifical robes and was entering before the Lord. Thus we do not say that the Pope cannot err in his private opinions, as did John XXII; or be altogether a heretic as perhaps Honorius was. Now when he is explicitly a heretic, he falls ipso facto from his dignity and out of the Church, and the Church must either deprive him, or, as some say, declare him deprived, of his Apostolic See, and must say as S. Peter did: Let another take his bishopric. When he errs in his private opinion he must be instructed, advised, convinced; as happened with John XXII, who was so far from dying obstinate or from determining anything during his life concerning his opinion, that he died whilst he was making the examination which is necessary for determining in a matter of faith, as his successor declared in the Extrazagantes which begins Benedictus Deus. But when he is clothed with the pontifical garments, I mean when he teaches the whole Church as shepherd, in general matters of faith and morals, then there is nothing but doctrine and truth. And in fact everything a king says is not a law or an edict, but that only which a king says as king and as a legislator. So everything the Pope says is not canon law or of legal obligation; he must mean to define and to lay down the law for the sheep, and he must keep the due order and form. Thus we say that we must appeal to him not as to a learned man, for in this he is ordinarily surpassed by some others, but as to the general head and pastor of the Church: and as such we must honour, follow, and firmly embrace his doctrine, for then he carries on his breast the Urim and Thummim, doctrine and truth. And again we must not think that in everything and everywhere his judgment is infallible, but then only when he gives judgment on a matter of faith in questions necessary to the whole Church; for in particular cases which depend on human fact he can err, there is no doubt, though it is not for us to control him in these cases save with all reverence, submission, and discretion. Theologians have said, in a word, that he can err in questions of fact, not in questions of right; that he can err extra cathedram, outside the chair of Peter, that is, as a private individual, by writings and bad example.
But he cannot err when he is in cathedra, that is, when he intends to make an instruction and decree for the guidance of the whole Church, when he means to confirm his brethren as supreme pastor, and to conduct them into the pastures of the faith.
First of all, it should be noted that St. Francis lays out the teaching of the Church with regard to the indefectibility (inability to fall away) and infallibility of the See of St. Peter. This is a crucial foundation for everything else. In the Catholic epistemology, the Church is infallible. The Magisterium of the Church cannot fall away into error or teach error authoritatively and bindingly upon the Church. And the See of St. Peter, the Pope, in particular, is protected from error and cannot lead the Church into error in his official and authoritative teaching. I would encourage readers to read the larger context of St. Francis's comments here, in which he makes crystal clear the indefectibility and unfailing reliability of the See of St. Peter. Also, see here and here for a more complete explanation of the Catholic view and all the nuances involved in it and citations for it from the sources of Catholic doctrine. I won't repeat all of that here, but it is a crucial foundation for understanding what we are going to discuss.
Can a Pope Err or Teach Heresy in His Private Capacity?
St. Francis articulates that Popes cannot err in their official, authoritative teaching. But he allows that they might be able to err as private individuals, when they are not teaching a doctrine authoritatively and bindingly to the Church. They might be able to err in their private opinions. They might even be able to be heretics in their private opinions (that is, their opinions might contradict the foundational doctrines of the faith). They might even articulate their errors or heresies explicitly and manifestly - that is, they might tell them to others or teach them. Is it true that a Pope might do that? Is that something that God might allow to happen? That is something upon which there has not been universal consensus among Catholic theologians, and there is no official teaching on this matter by the Church. There is a range of opinions that can be held here, within the boundaries laid down by what the Church has taught (and especially with regard to the Church's teachings on the indefectibility and infallibility of the Church, the Church's Magisterium, and the Roman See). St. Robert Bellarmine, another Doctor of the Church, is famous for holding the position that it is most probable that God would not allow a Pope to fall into manifest heresy even as a private person. (See De Controversiis: Tomus I: On the Roman Pontiff, Book IV, VI). It seems to me that the doctrine of the indefectibility and infallibility of the Roman See does not absolutely or conclusively rule out the possibility of a Pope believing or teaching error or even heresy in his private capacity, since such teaching, by its very nature, would not bind the Church to error or enter into her official teaching.
What Would Happen If a Pope Taught Error or Heresy in His Private Capacity?
So what would happen if a Pope taught error or heresy in his private capacity? St. Francis de Sales, in the quotation above, gives the common opinion on this among Catholic theologians through history: "Now when he is explicitly a heretic, he falls ipso facto from his dignity and out of the Church, and the Church must either deprive him, or, as some say, declare him deprived, of his Apostolic See, and must say as S. Peter did: Let another take his bishopric. When he errs in his private opinion he must be instructed, advised, convinced." If the Pope has kept his opinions to himself, of course, since there is no public knowledge of them, nothing can be publicly done about them. If he is known to err in some lesser matter, he can be instructed and corrected. But if he errs more fundamentally, by holding to heretical opinions (again, opinions that contradict the foundational doctrines of the Church), and has manifested those opinions publicly, St. Francis says that, by that act, he has basically cast himself out of both the papal office and the Church itself, and the Church can recognize this and depose him or declare him deposed. This opinion has been common among Catholic theologians.
The Church has not issued any official teaching about this possibility in recent times, nor is there anything at all about this in current canon law. However, as I've said, what St. Francis has laid out has been the common opinion among theologians. Also, there have been statements made about this subject in the past in collections of canon law and by Popes. The reader can see some of these statements and some statements by important theologians of the past on this matter in this very brief and helpful article by Erick Ybarra. For example, in the Decretum Gratiani, which was a collection of Church rules from earlier days and was a central source of canon law in the 12th and 13th centuries and significantly informed much later canon law, we find the principle articulated that "No mortal shall presume to rebuke his [the Pope’s] faults, for he who is to judge all is to be judged by no one, unless he is found straying from the faith" (Decretum Gratiani, Dist. 40, c. 6; translation in Patrick Granfield, The Limits of the Papacy [New York: Crossroad Publishing Company, 1987], 71, found here). Pope Innocent III (who was Pope from 1198-1216) is famous for laying out more commentary on what this meant, saying that "only on account of sin committed against the faith can I be judged by the church" (Patrologia Latina 217, 656; Translation in Jaroslav Pelikan, Reformation of the Church and Dogma (1300-1700), The Christian Tradition: A History of the Development of Doctrine, vol. 4 [Chicago: University of Chicago Press, 1984], found here). Pope Innocent III elaborated further on this concept:
Nevertheless he [the pope] should not mistakenly flatter himself about his power, nor rashly glory in his eminence or honor, for the less he is judged by man, the more is he judged by God. I say "less" because he can be judged by men, or rather shown to be judged, if he clearly loses his savor to heresy, since he "who does not believe, is already judged." It is only in this case that it should be understood of him that, "If the salt loses its savor, it is good for nothing anymore, except to be thrown out and to be trodden on by men." (Pope Innocent III, Between God and Man: Six Sermons on the Priestly Office, trans. Corinne J. Vause and Frank C. Gardiner [Washington, DC, Catholic University of American Press, 2004), 48-49, found in Erick Ybarra, The Papacy: Revisiting the Debate between Catholics and Orthodox [Steubenville, OH: Emmaus Road Publishing, 2022], 534)
Innocent III here indicates the same nuance we see in other theologians - namely, that if the Church should judge a Pope for his heresy, it is not so much that the Church is judging the Pope herself as that she is officially recognizing a judgment already passed on the Pope by God. It has been frequently stated by many Popes and theologians and has always been and currently is stated in canon law (see canon 1404) that "the First See is judged by no one." There is no higher human authority in the Church than the Pope, who thus cannot be judged by equal or lower levels of authority in the Church. But the Pope is obviously subject to God, and the Church can recognize the judgment of God.
So it has been acknowledged in the past that if a Pope were to fall into manifest heresy, he might be judged by the Church in this way. But, as I said earlier, this teaching is not currently a part of canon law. Could this be because such a thing could not happen, as Bellarmine and others have thought? Perhaps, but, so far as I can tell at this point based on what I've seen, I don't think there is enough evidence to say for sure.
Since we are dealing here with something as extreme as the deposition of a reigning Pope from office, we have to proceed here with extreme caution, making very sure that we don't jeopardize the indefectibility of the Church or the unfailing reliability and supreme jurisdiction of the Magisterium and the Roman See in our opinions. As Bellarmine points out, this has never happened in the two-thousand-year history of the Church. (He points this fact out partly to use it to argue that such a thing probably could never happen.) There is one case in Church history where a Pope was condemned for heresy: Pope Honorius was condemned as a heretic by the Sixth Ecumenical Council in 681. But, in this case, the condemnation occurred decades after Honorius's death, and the condemnation was ratified by the Pope who was reigning at that time, Leo II (without whose ratification the council's condemnation could have had no validity). (The Honorius affair is complex and filled with all sorts of nuances, so I will refer readers here for more on this. For one thing, it is not clear that Honorius was actually a heretic in the sense of actually believing or teaching false doctrine; his condemnation can be interpreted as due not so much to his actual opinion as to his failing to be careful enough in his words to avoid aiding and abetting a heretical movement that actually really got going only after his death.) There has never been a case where a currently-reigning Pope has been legitimately deposed from office by the Church. So as we consider this hypothetical possibility (which may or may not be actually possible), we have to make sure our thoughts are consistent with Catholic teaching and Catholic epistemology.
If a Pope were to be deposed from office for heresy, the proceedings of the Church against the Pope would have to be done with full Magisterial authority. This could not be a matter of one group of theologians (even if they are priests or bishops) arguing against other groups, with no official sanction, that some teaching of the Pope was heretical. For example, some people argue that Pope Francis's teaching on the death penalty is at least something like heretical because it contradicts earlier definitive Church teaching on this subject. But this is not at all clear and certain, and in fact I think it is evidently wrong (see here for more on this), and in any case they cannot cite their opinion as the authoritative position of the universal Magisterium. Going along with this, the proceedings would have to be done according to clear and recognized rules, so that everyone would be able to recognize them as a legitimate Magisterial act. Personally, I'm not sure how that could be done without there being some clear procedure laid out in canon law, which there currently is not. If this scenario is at all a real possibility, my recommendation is that theologians and Church officials should work hard and give some real thought to trying to figure out how we should think about these things so that we can perhaps come to some conclusive and officially-recognized theological position on these matters, and I would also recommend that, if the Church decides that, yes, this could happen, she would consider laying out very clear and explicit procedures for such an eventuality in canon law. In that way, if this ever happened, hopefully there would be no reasonable doubt as to how to proceed. The procedures followed would have the clear imprint of Magisterial and papal authority. The situation, in that case, would be much like what happens when a reigning Pope dies. In the time between the death of the last Pope and the election of the new Pope, chaos does not ensue because the Church has clear procedures to follow in such a case. Of course, God can protect the Church from falling apart even without such clear procedural rules, and he has many times in the past, and we know he will because that is his fundamental promise to the Church, yet the Church is morally obligated to do her due diligence in trying to avoid the negative consequences of her own negligence. It would be to the Church's detriment if God has to protect her over and against her own negligence. And even if we can be sure the Church would not fundamentally fall away, yet still the Church's negligence could lead to many bad results and schisms.
If there was a clear procedure laid out in canon law as described above, ratified by Magisterial (including papal) authority, then it could be carried out without violation of that authority. But what if the Pope protests that he is not a heretic, or that the judgment against him is incorrect or without authority? If he protests in his private capacity, simply as a member of the Church, this would not seem to be a problem. But what if he were to protest in his official capacity as Pope? As we have noted, the Pope has supreme jurisdiction in the Church and is also incapable of leading the Church into error in his official, authoritative teaching. The Pope's authority and protection from error in these matters is precisely on the same level as that of the whole episcopate (for the episcopate necessarily includes the Pope and the Pope necessarily speaks authoritatively for the whole episcopate), so there is no possibility for the Church to contradict or overrule the Magisterial authority of the Pope. If the Pope were to give an authoritative teaching declaring his own teaching orthodox, or if he were to declare the whole procedure against him void, the Church would have to submit to that. So there could be no declaring the Pope a heretic or deprived from office if the Pope were to oppose this in his official capacity. (But see the next section for another possible twist on this point.)
Could a Pope Teach Error or Heresy in an "Official" Form but Ultra Vires?
I want to throw out a hypothetical scenario for discussion that I have not heard anyone address before. Perhaps this has been addressed and I am not aware of it, but it seems worth discussing. Could it ever happen that a Pope might attempt to issue not a private but an authoritative teaching, whether definitively or non-definitively, but fail to do so due to the teaching being ultra vires - that is, beyond his competent authority? For example, imagine that a Pope issues a statement claiming, in an ex cathedra manner, that the doctrine of the Trinity is incorrect and that there is instead a divine Quaternity. Could this ever happen? Of course, Church teaching is crystal clear that there could never be any real ex cathedra teaching from a Pope that is heretical, for here papal infallibility is in effect at its highest degree. But perhaps, in such a scenario as I've laid out, the teaching might be considered a false claim of ex cathedra teaching. We know that the Pope has supreme human jurisdiction in the Church, including in the teaching of doctrine. But we also know that the Popes are servants of God and his revelation. They have no authority to contradict God. If a Pope attempted to give an ex cathedra teaching that contradicted divine revelation, then, that attempt would be ultra vires - beyond the authority he has been granted by God. It would be like the governor of Idaho attempting to make an executive order for the State of Missouri. In such a case, then, although the outward form of the teaching is ex cathedra and the Pope is attempting to give an ex cathedra teaching, the teaching would in reality have no papal or Magisterial authority at all. It would be, in authority, equivalent to a private teaching of the Pope.
Could such a scenario ever happen? I don't know. I currently cannot think of any reason to consider it inherently impossible, because it would not threaten the indefectibility of the Church or contradict Magisterial or papal infallibility. Of course, in order not to threaten the indefectibility of the Church and the Pope, God would only allow this to happen in cases where the "papal" teaching is so obviously heretical as to leave no room for reasonable doubt on the subject. There would have to be absolutely manifest, clear heresy, recognized as such clearly and universally by the Church. An example of a clear and clearly-and-universally-recognized heretical teaching would be an explicit and clear denial of the doctrine of the Trinity, or the clear and explicit affirmation of some other contrary doctrine (like a divine Quaternity or something like that). There would be no reasonable doubt in such a case that the Pope had expressed heresy and had contradicted previously-given definitive Magisterial teaching. Since we are obligated to follow the judgment of the Pope as of supreme authority on earth, as he exercises his office as the Vicar of Christ, we would only be authorized to reject a teaching coming from him if that teaching were so clearly heretical that there could be no doubt, and it would be basically universally recognized in the Catholic Church, that that teaching is not a true papal teaching but is ultra vires. All the things I said in earlier sections about this not being able to happen with disputable teachings, or judged by private theologians or groups of theologians or bishops, etc., would apply here in the same way as they applied to the earlier scenarios we considered. If the Pope were to be judged and even possibly deposed in such a scenario, it would have to be by means of clearly-recognized Magisterial authority operating with clearly-recognized procedural rules.
Brief Excursus on the Possibility of Other Forms of Ecclesiastical or Other Judgments Being Enacted against Popes
The Church has made it clear that "the First See is judged by no one," and statements by Popes and in canon law collections in the past have limited the possibility of the Church judging the Pope to cases of heresy, but is it possible to consider that there might be ways in which Popes, as human persons subject like all of us to sin, imprudence, incompetence, negligence, etc., could be judged for other things by the Church? There is a lot of discussion in the Church today about keeping priests and bishops accountable (such as with regard to sexual sins and crimes and other things). Must the Pope remain unaccountable in all of these areas? Or could papal authority be consistent with some forms of papal accountability?
It is clear that, in the Catholic Church, the Pope has supreme jurisdictional and doctrinal authority. So there can never be the kind of papal accountability that would threaten those things. We have to trust that God will keep the Popes adequately accountable, since they are ultimately subject to his judgment. But what if the Magisterium, including the Pope, were to put procedures into canon law for papal accountability, much as there are procedures for accountability of other persons in the Church? In such a case, the laws would be legitimate, because established with legitimate Magisterial and papal authority. Of course, there would always be the possibility that a Pope could overrule such procedures, since to deny this possibility would be to remove the supreme jurisdiction of the Pope, but at least there would be procedures in place that Popes would be ordinarily expected to follow, imposed upon them with papal authority. There would be some moral force to these laws, even if that force is not jurisdictionally superior to papal jurisdiction, for if a Pope were to refuse to submit to such laws he would be going against established norms in the Church and against what his predecessors in the papacy or even he himself had previously established as important for the good of the Church, and this would reflect very badly on him. Unless he had very good and clear reasons to refuse to submit to those laws, he would be publicly highlighting what would at least appear to be an unreasonable flaunting of his personal moral responsibility and thus would bring significant dishonor and perhaps even scandal upon himself, on the papal office, and on the Catholic Church. Perhaps there could even be decrees or rules passed regarding papal accountability that would be definitive in nature, so that it would be ultra vires for a Pope to overturn them in the future. I think there are some things at least worth considering here.