For more resources on this subject, see our earlier article “Catholicism.”
In Roman Catholicism, the Pope is the “Vicar of Christ.” Vicar means “substitute.” Students of the Bible are often familiar with the term “vicarious atonement” which is another way of saying “substitutionary atonement.” Since the Pope is the Vicar of Christ on Earth, Roman Catholicism has taught the doctrine of papal infallibility.
Infallibility comes from the roots in (meaning “not”) and fallere (meaning “to deceive”). According to Roman Catholic authorities, infallibility is “immunity from error, i.e., protection against either passive or active deception. Persons or agencies are infallible to the extent that they can neither deceive nor be deceived.” Vatican I explains,
The Apostolic See and the Roman Pontiff hold primacy over the whole world, and that the Pontiff of Rome himself is the successor of the blessed Peter, the chief of the apostles, and is the true vicar of Christ and head of the whole Church and faith, and teacher of all Christians; and that to him was handed down in blessed Peter, by our Lord Jesus Christ, full power to feed, rule, and guide the universal Church, just as is also contained in the records of the ecumenical Councils and in the sacred canons.
Catholic apologists Kreeft and Tacelli write,
Catholics believe that God preserved the Church’s magisterium from ever officially embracing and teaching error in faith and morals. Practical, tactical, strategical, pastoral mistakes were made. But not creedal mistakes. For two thousand years God providentially protected popes and councils made up of selfish, shallow and sinful people from ever officially teaching a single heresy. It’s like a baseball team playing for two thousand years without make a single error.
The doctrine of papal infallibility does not mean that the Pope has all of the answers regarding faith and morals. Instead, it simply means that he cannot teach error. He can abstain from speaking on certain topics, if he is not sure what to say. Catholic apologist Karl Keating gives the illustration of the Pope leaving the answers blank on a test. This would fit with infallibility. The Pope could leave the answers blank, as long as he didn’t mark them incorrect.
It is a common misconception to believe that the Pope is infallible on everything that he teaches. However, as we see above, this is not true. If the Pope predicts the stock market or the weather, he can be wrong. Infallibility only applies to proclamations about faith and morals, and this is only when he speaks ex cathedra. The Catholic Encyclopedia, citing the Vatican Council (Sess. IV, Const. de Ecclesiâ Christi, c. iv), defines ex cathedra states in this way:
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.
However, speaking ex cathedra is hotly disputed. Geisler and MacKenzie write,
There are many hotly disputed differences among Catholic scholars on just what ex cathedra statements mean, including those on Scripture, tradition, Mary, and justification. Even though there may be future clarifications on some of these, the problem remains for two reasons. It shows the indecisive nature of supposedly infallible pronouncements, and, judging by past experience, even these future declarations will not settle all matters completely.
Therefore, it becomes difficult (or impossible) to falsify papal doctrine. If a teaching of a past pope is false, it is difficult to ascertain if this was an official (ex cathedra) statement. Of course, Roman Catholicism teaches that the pope cannot give new revelation from God. Catholic apologist Karl Keating writes,
The clear teaching of the Bible is that after the death of the last apostle no further revelation is to be made… The Pope and the bishops are not inspired the way the authors of Scripture or the prophets were. To make a new definition, to clear up some dogmatic confusion, they first must use reason, operating on what is known to date, to be able to teach more precisely what is to be held as true.
Catholic apologist Dave Armstrong writes,
Development of doctrine is defined by Catholics as the increase in understanding… of Christian doctrines that originated from the Lord Jesus himself and which have been passed down through the Apostles, the Fathers, the councils, and the Catholic Church in general… The Catholic Church maintains that no new public revelation has been received by the Church since the time of the Apostles.”
Instead, his doctrinal statements are based on the traditions of the apostles handed down through history. They base this on passages like 2 Thessalonians 2:15, 1 Corinthians 11:2, and 3 John 13. In other words, if a holy tradition was passed down through the church fathers, then a modern pope can declare this as true. However, Roman Catholicism does not state that these are new revelations. Instead, according to their view, these are old revelations that have been ratified as true by the Pope.
 Avery Dulles, “Infallibility: The Terminology,” in Teaching Authority, ed. by Empie, p. 71. Cited in Geisler, Norman L., and Ralph E. MacKenzie. Roman Catholics and Evangelicals: Agreements and Differences. Grand Rapids, MI: Baker, 1995. 203.
 Denzinger, Sources of Catholic Dogma, pp. 455–56. Cited in Geisler, Norman L., and Ralph E. MacKenzie. Roman Catholics and Evangelicals: Agreements and Differences. Grand Rapids, MI: Baker, 1995. 204.
 Kreeft, Peter, and Ronald K. Tacelli. Handbook of Catholic Apologetics: Reasoned Answers to Questions of Faith. San Francisco: Ignatius, 2009. 433.
 Keating, Karl. Catholicism and Fundamentalism. San Francisco: Ignatius, 1988. 215.
 Geisler, Norman L., and Ralph E. MacKenzie. Roman Catholics and Evangelicals: Agreements and Differences. Grand Rapids, MI: Baker, 1995. 215-216.
 Keating, Karl. Catholicism and Fundamentalism. San Francisco: Ignatius, 1988. 142, 146.
 Armstrong, Dave. A Biblical Defense of Catholicism. Manchester, NH: Sophia Institute, 2003. 64, 65.