The belief in papal infallibility was defined as dogma by Pope Pius IX in Pastor aeternus:
“We teach and define that it is a dogma Divinely revealed that the Roman pontiff when he speaks ex cathedra, that is when in discharge of the office of pastor and doctor of all Christians, by virtue of his supreme Apostolic authority, he defines a doctrine regarding faith or morals to be held by the universal Church, by the Divine assistance promised to him in Blessed Peter, is possessed of that infallibility with which the Divine Redeemer willed that his Church should be endowed in defining doctrine regarding faith or morals, and that therefore such definitions of the Roman pontiff are of themselves and not from the consent of the Church irreformable. So then, should anyone, which God forbid, have the temerity to reject this definition of ours: let him be anathema.”
The problem with papal infallibility is that it is impossible to defend historically. There have been many instances where a pope taught as doctrine things which later popes came to reject:
1. Pope Honorius I taught the error of monotheletism in his letter to Sergius I of Constantinople when he said, “We confess one will of our Lord Jesus Christ.” His teachings were condemned at the Sixth Ecumenical Council. I encourage you to listen to the debate between James White and Tim Staples on papal infallibility to see how indefensible it is. If you had died believing in the teachings of Honorius, you would have died as a heretic.
2. Pope Boniface VIII in Unam sanctam declared that submission to the Roman Pontiff is absolutely necessary for salvation. But today, the Catholic Church has completely redefined what “No Salvation Outside the Church” means. They also teach that Jews don’t need to believe in the gospel to be saved and that Muslims and Christians worship the same God.
3. Pope Pelagius II in Dilectionis vestrae and Pope Eugene IV in Cantate domino declared that Jews who do not become communicant members of the Catholic Church cannot be saved. This stance was overturned at Vatican II and by Pope Francis.
4. Pope Zosimus gave approval to the theology of Pelagius and opposed Augustine and the North African bishops before reversing his decision only after facing pressure from the emperor.
6. Pope Pius IX in his Syllabus of Errors opposed religious liberty and the separation of church and state.
9. Multiple popes taught that Mary was not immaculately conceived.
10. Pope Leo X in Exsurge Domine taught that it is in accordance with the mind of the Spirit to burn heretics to death.
12. Pope Innocent I, Pope Leo the Great, and Pope Gregory the Great taught that deacons must have no sexual relations with their wives.
13. Pope Gregory the Great condemned the idea of a universal bishop calling it a blasphemous title.
14. Pope Vigilius refused to condemn “The Three Chapters” of the writings of Theodore of Mopsuestia, Theodoret of Cyrus, and Ibas of Edessa. He initially condemned them but then reversed his decision and refused to condemn them because they were already dead. The Fifth Ecumenical Council then condemned them and anyone who refused to condemn them. Vigilius then reversed his decision a second time and condemned them.
15. Pope Eugenius IV opposed the Council of Basel which reaffirmed the Council of Constance’s teaching on conciliarism. Eugenius eventually reversed his decision and approved the teachings of the council. But conciliarism was finally condemned at the Fifth Lateran Council and Vatican I after being approved by two previous ecumenical councils.
16. Pope Paul V, Pope Urban VIII, and Pope Alexander VII condemned Galileo for teaching the heliocentric model of the solar system as being contrary to the teachings of Scripture. Some Catholics even today still believe in geocentrism.
18. Pope Gelasius I denied the doctrine of transubstantiation by teaching that the nature of bread and wine remain the same during the Eucharist. Without transubstantiation, there can be no sacrifice of the Mass or worship of the Eucharist.
19. Pope Pius V in Quo primum taught that the practice of the Mass is to remain unchanged “henceforth, now, and forever, throughout all the provinces of the Christian world” which was overturned by Vatican II.
20. Pope Hormisdas rejected the Transitus Beatae Mariae as heretical which is the first historical witness to a belief in the bodily assumption of Mary.
21. Pope Pius IX misinterpreted Genesis 3:15 in Ineffabilis Deus based on a textual variant in the Latin manuscript tradition.
22. The Seventh Ecumenical Council’s decrees on modesty of dress have been completely thrown out the window by the modern papacy.
23. The papacy has historically taught that the Donation of Constantine is genuine.
24. The papacy teaches that the Shroud of Turin is the original burial cloth of Jesus despite the evidence to the contrary.
25. Pope John Paul II and Pope Francis both teach that the theory of evolution is true in contrast to Pope Pius X who condemned theistic evolution.
26. Pope Francis teaches that, “It is not licit to convince them of your faith. Proselytism is the strongest venom against the ecumenical path” in a speech to a group of Lutherans. Contrast this attitude with that of Augustine as cited approvingly by Pope Leo XIII in Satis cognitum: “You are not to be looked upon as holding the true Catholic faith if you do not teach that the faith of Rome is to be held.”
27. Pope Francis believes that Martin Luther’s doctrine of justification was correct in contrast to Pope Leo X in Exsurge Domine.
28. Pope Francis has redefined the Catholic Church’s teaching on cohabitation by giving approval to some cohabitating relationships. Many Catholics have accused him of heresy for his teachings on divorce and remarriage.
The changes that Francis has made have caused many Catholics to leave their faith and become atheists jettisoning science in the process. But please remember, just because the pope is a deceiver does not mean that Jesus Christ was a deceiver. True biblical Christianity existed long before Catholicism or Eastern Orthodoxy did and is still changing lives. It is built on the foundation of Scripture and fulfilled prophecy.
I realize that not all of these examples fit the definition of papal infallibility in Pastor aeternus. But the documents Unam sanctam, Cantate domino, Exsurge Domine, Quo primum, and Unigenitus certainly do since they were invoking the power and protection of God in their declarations.