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CNA Staff, Dec 8, 2025 / 06:00 am (CNA).

On Dec. 8 the Catholic Church celebrates the solemnity of the Immaculate Conception — a paramount feast in the Church’s liturgical calendar and one that indirectly touches on a regularly misunderstood but important piece of Church dogma.

The solemnity is the patronal feast of the United States and marks the recognition of the Blessed Mother’s freedom from original sin, which the Church teaches she was granted from the moment of conception.

The Catechism of the Catholic Church states that Mary was “redeemed from the moment of her conception” (No. 491) in order “to be able to give the free assent of her faith to the announcement of her vocation” (No. 490). 

The dogma was disputed and challenged by Protestants over the centuries, leading Pope Pius IX to affirm it in his 1854 encyclical Ineffabilis Deus, stating unequivocally that Mary “was endowed with the grace of the Holy Spirit and preserved from original sin” upon her conception. 

Ineffabilis Deus is among the papal pronouncements that theologians have long considered to be “infallible.” But what does papal infallibility mean in the context and history of the Church?

Defined by First Vatican Council in 1870

Though Church historians argue that numerous papal statements down through the centuries can potentially be regarded as infallible under this teaching, the concept itself was not fully defined by the Church until the mid-19th century.

In its first dogmatic constitution on the Church of Christ, Pastor Aeternus, the First Vatican Council held that the pope, when speaking “in the exercise of his office as shepherd and teacher of all Christians, in virtue of his supreme apostolic authority,” and while defining “a doctrine concerning faith or morals to be held by the whole Church,” possesses the infallibility that Jesus “willed his Church to enjoy in defining doctrine concerning faith or morals.”

Father Patrick Flanagan, an associate professor of theology at St. John’s University, told CNA that the doctrine of papal infallibility “does not concern the pope’s character.”

“The pope is human,” Flanagan said. “In other words, he is fallible. He can sin and err in what he says about everyday matters.”

Yet in “rare historical, narrowly defined moments” when the pope “exercises his authority as the supreme teacher of the Church of the Petrine office” and speaks “ex cathedra,” he is guided by the Holy Spirit to speak “indisputable truth” about faith and morals, Flanagan said. 

Flanagan underscored the four specific criteria that a papal statement must make to be considered infallible. For one, the pope must speak “in his official capacity as supreme pontiff,” not off-the-cuff or informally. 

The doctrine, meanwhile, must concern a matter of faith or morals. “No pope would speak ex cathedra on scientific, economic, or other nonreligious subjects,” Flanagan said. 

The statement must also be “explicitly straightforward and definitive,” he said, and it “must be intended to bind the whole Church as a matter of divine and Roman Catholic faith.” 

John P. Joy, a professor of theology and the dean of faculty at St. Ambrose Academy in Madison, Wisconsin, told CNA that the doctrine can be identified in part by the reading of Matthew 16:19.

In that passage, Christ tells Peter, the first pope: “I will give you the keys to the kingdom of heaven. Whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven.”

“Part of what Jesus is promising here is that he will endorse and ratify in heaven all of the judgments that Peter makes on earth,” Joy said. 

“So when Peter (or one of his successors) turns the key, so to speak, that is, when he explicitly declares that all Catholics are bound to believe something on earth, then we have the words of Jesus assuring us that God himself will hold us bound to believe the same thing in heaven,” he said. 

Though the concept of papal infallibility is well known and has become something of a pop culture reference, the number of times a pope has declared something infallibly appears to be relatively small. 

Theologians and historians do not always agree on what papal statements through the centuries can be deemed infallible. Joy pointed to the Immaculate Conception, as well as Pope Pius XII’s declaration on the Assumption of the Blessed Virgin in 1950, as two of the most well known.

He pointed to numerous other statements, such as Pope Benedict XII’s Benedictus Deus from 1336 and Pope Leo X’s Exsurge Domine in 1520, as infallible statements. 

Flanagan pointed out that there is “no official list” of papally infallible statements. Such declarations are “rare,” he said. “A pope invokes his extraordinary magisterial powers sparingly.” 

When Catholics trust a papally infallible statement, Joy stressed, they “are not putting [their] faith in the pope as if he were an oracle of truth or a source of divine revelation.” 

“We are rather putting our faith in God, whom we firmly believe will intervene in order to stop any pope who might be tempted to proclaim a false doctrine in a definitive way,” he said. 

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