Rev. Joseph L. Iannuzzi, STD, Ph.D. has written an in-depth article answering the question: Can a Pope Become a Heretic? [PDF file] Please download a copy and take the time to read it.
Rev. Joseph Leo Iannuzzi is a doctoral alumnus of the Gregorian Pontifical University. He has obtained 5 post-graduate degrees, with studies in medicine, anthropology, sociology, philosophy, and theology. As a young medical student, Joseph traveled to a Marian shrine in 1988 where he was inspired to enter the seminary. In 1991 he obtained a Ph.B. in Philosophy and was awarded the Kilburn Award. While assigned for 15 years in Italy, Rev. Iannuzzi studied Italian, Hebrew, Greek, Latin and other languages. He also obtained an STB, M. Div., STL and STD, Ph.D. in Theology, with specialization in patristics, dogmatics and mysticism.
I will offer a few quotes from the article, but I recommend reading it, in its entirety.
“In recent months the Roman Pontiff’s teaching authority has been openly challenged and his supreme, full and immediate authority questioned. Particular exception has been taken to his non ex cathedra pronouncements in light of modern prophecies which, according to some, have troubled not a few Catholics. As a result, many Catholics have written yours truly asking for clarification in this regard. In response, I offer the following article to help dispel any confusion surrounding the Roman Pontiff’s teaching authority, and herewith, a clear answer from Church Tradition and Magisterial documents pertaining to the type of assent required from all the faithful to the Roman Pontiff, even when he is not speaking ex cathedra.”
Fr. Iannuzzi refers to persons and groups who detract from the full authority of the Roman Pontiff, in one way or another, as “sedeists”. He then explains his position on the question of Popes and heresy:
“In contrast to the sedeists’ position, my theological response demonstrates, through the founts of Sacred Scripture, Church Tradition and Magisterial documents, that no Roman Pontiffs of the past have made heretical statements and to them the title heretic may nowise be imputed. Drawing from Sacred Scripture and Tradition, one sobering truth emerges: the heretical statements the sedeists attribute to Roman Pontiffs are cited out of context and/or were uttered before the Church made any official doctrinal pronouncement on the doctrinal issues the Pontiffs addressed. In point of fact, throughout 2,000 years of Church history not one validly elected Roman Pontiff has ever contradicted one official doctrinal pronouncement of the Church.”
In the main body of the article, Fr. Iannuzzi then goes on to give examples of Popes who have been accused of being heretics or of teaching heresy. He defends each Roman Pontiff against these accusations, and concludes that no Pope has ever committed or taught heresy.
“In view of the documentary evidence provided in this presentation, one may affirm that the sedeist views toward the Roman Pontiff’s teaching authority, even when he is not speaking ex cathedra, is flawed and spiritually harmful, as it brings with it the danger of judging the Pope according to one’s own standards and falling short of the obedience asked of them by Christ.”
…
“I here recall Christ’s words to Peter who alone among the Apostles received direct knowledge from above: ‘Blessed are you, Simon son of Jonah. For flesh and blood has not revealed this to you, but my heavenly father. And I say to you, you are Peter, and upon this rock I will build My Church, and the gates of the netherworld shall not prevail against it’ (Mt. 16.17-18).
“In these words, Christ does not tell Peter to build his church, but that He himself will build his own Church, thereby implying that through Peter (who represents all future Pontiffs) Christ accomplishes his Divine Will within his Church by the power of the Holy Spirit whom he promised to send his Apostles to ‘lead them to all the truth’ (Jn. 16:13). It is precisely this promised Holy Spirit who continues to inspire each Roman Pontiff to guide the Church in every generation.”
In support of his conclusion, Fr. Iannuzzi quotes Ecumenical Councils and the Catechism of the Catholic Church. He also cites Doctor of the Church, Saint Robert Bellarmine:
“There are five opinions about this matter. The first is that of Albert Pighi (Hierarch. Eccles., lib. 4, cap. 8), for whom the Pope cannot be a heretic and therefore cannot be deposed in any case. This opinion is probable and can be defended easily….”
Then Fr. Iannuzzi writes the following:
“The theologian Francisco de Suarez (1548-1617), a contemporary of R. Bellarmine, was sure that God’s ‘sweet providence’ would not allow the Pope who could not teach error to fall into error, and that this was guaranteed by the promise, ‘I have prayed for you (Simon) that your faith may not fail…’ (Luke 22: 32)….
“Much like Bellarmine and Suarez, Saint Alphonsus Liguori (1696-1787) did not believe that God would ever permit a Roman Pontiff to become a heretic, not even as a private person. He affirms: ‘We ought rightly to presume as Cardinal Bellarmine declares, that God will never let it happen that a Roman Pontiff, even as a private person, becomes a public heretic or an occult heretic.’ ”
In conclusion, let me add that many of the current commentators, who propose that multiple Popes in the past have committed or taught heresy, make that claim so as to undermine the teaching authority of the current Roman Pontiff, Pope Francis. So it is not merely an historical or academic question. The Catholic laity are discussing this issue online, and many of them have become convinced that a Pope can fall into heresy, and that Pope Francis has or might fall into heresy. In this way, souls are being harmed. So it is very important for all faithful Catholics to understand that the Ark of Salvation, the Church, can never go astray, and Her pilot and navigator, the Roman Pontiff, likewise, by the grace of God, cannot himself go astray.
Popes are fallen sinners, and their personal theological opinions can err. But no Pope has ever or can ever commit or teach heresy. For Jesus founded the Church on the Rock that is Peter and his successors, and that Rock can never fail.
by
Ronald L. Conte Jr.
Roman Catholic theologian and translator of the Catholic Public Domain Version of the Bible.
Please take a look at this list of my books and booklets, and see if any topic interests you.
the reproach of Christ 
I think that the question has been settled in Pastor Aeternus.
How can the Pope receive a never-failing faith and become a heretic, considering that we know very well that heresy is the loss of the faith?
If the Pope receives a never-failing faith he cannot become a heretic, if he becomes a heretic he never received the never-failing faith.
The discussion was legit when the First Vatican Council was still “in mente Dei”. Now, it is not (unless we are ready to face the possibility that a Council can make DOGMATIC errors, but this would be the self-destruction of the Church, because a Church that errs dogmatically when she claimed that this is impossible would be just another human structure).
I repeat what i wrote in the previous article: these folks are trying to surreptitiously deny the dogma of papal infallibility because they can’t stand that a Pope can be right even if he is not a draconian conservative.
It really is that simple.
And yet, God has apparently allowed, or it is seemingly God’s will, that the Church He founded be divided on discipline and no longer speak with one voice. Discipline may not be doctrine per se, but the divergent application of that discipline hinges on definitional terms that are doctrinal in nature – what is “adultery”? What is “conversion” such that it is sufficient to no longer be considered to be repeatedly committing adultery? These are clearly being defined differently in San Diego as compared to Philadelphia.
Cardinal Mueller (our current guardian of the Doctrine of the Faith) claims quite loudly that AL doesn’t say what the Bishops of Buenos Aires and San Diego say it says. Francis remains silent, seemingly giving consent to both sides of the dispute. And so the Church has become a provincial enterprise in this regard. Not good fruit, that.
Saints Paul and Barnabas disagreed vehemently about John Mark, the Gospel writer: “And there occurred a dissension, to such an extent that they departed from one another.” (Acts 15:39). The Church is filled with fallen sinners. So we should not be dismayed that contentions and problems occur. No Pope is perfect. (And we know that the first Pope was Peter, not Jesus.)
@Jack
“What is “conversion” such that it is sufficient to no longer be considered to be repeatedly committing adultery?”
Whop said that? Adultery is adultery, and is always grave matter, is always an objective mortal sin.
But situations can occur when one’s freedom to act otherwise without a further guilt is diminished due to mitigating factors (see the Catechism at paragraphs 1757, 1860, 1862, 1735, 2283, 2355), and in these situations the objective mortal sin of adultery is not an actual mortal sin.
How could you agree with this statement : “my theological response demonstrates, through the founts of Sacred Scripture, Church Tradition and Magisterial documents, that no Roman Pontiffs of the past have made heretical statements and to them the title heretic may nowise be imputed” while the Third Council of Constantinople (Sixth ecumenical), has anathemathize pope Honorius (et Honorium qui fuit papa antiquae Romae, in COD, t. 2-1, p. 125). A theological demonstration can’t cancel a fact (I’ll not demonstrate that Vatican I is no opposite to the fact that a Pope could become heretic. It has often been done…)
You only speak about Magisterium, and you don’t care about an ecumenical council ! It’s amazing !
An Ecumenical Council can exercise both the Magisterium (authority over doctrine) and the temporal authority (over discipline). When the Council is not teaching, but judging cases, its decisions are fallible. The teaching of Vatican I on the never-failing faith of each Pope, is doctrine, and therefore supersedes and nullifies the fallible judgment of the Sixth Council. Judgments of Popes and Councils on matters other than doctrine are reformable. Infallible teachings are irreformable.
Honorius was negligent in not opposing and extinguishing the heresy of Monothelitism. But he did not teach that error publicly, and in his private letters, he does not seem to have decided the question (which is often over-simplified as ‘one will or two’), even in his own mind and heart. So he did not teach or hold any heresy.
@Cyrille
If you don’t mind, could you explain me how a Pope can receive a never-failing faith and still become a heretic, when it’s obvious that an heretic Pope would clearly nullify the former assumption (because a never-failing faith that, ultimately, fails -for heresy is the destruction of one’s faith- is clearly NOT never-failing)?
Thanks!