An Unfailing Treasure: ‘Pastor Aeternus’ and defining papal infallibility

Mention the First Vatican Council and you may hear the reply, “Oh, that’s when the pope said he was infallible.” The comment is not completely wrong, but it’s not completely right, either.

Papal infallibility was defined at the First Vatican Council via the dogmatic constitution Pastor Aeternus (July 18, 1870). But the definition was given not by the pope alone — Pope Pius IX, who reigned from 1846 to 1878; the majority of bishops signed on, too.

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Pastor Aeternus considered more than papal infallibility, however. Its main objective, in fact, was to clarify the pope’s authority to act as chief shepherd and teacher of the Church — or, in other words, to fulfill the Petrine office established by Jesus: “And so I say to you, you are Peter, and upon this rock I will build my church” (Mt 16:18).


As Pius IX began his papacy on June 21, 1846, ideas of extreme church-state separation and rationalism’s supremacy over faith that marked the French Revolution of 1789 still hung in the air throughout Europe. In Italy, nationalists wanted to strip the pope of all temporal power. The pope fled the Vatican in 1848 and returned two years later with his rule restored. However, it only lasted for 20 years when, in 1870, the Church lost all of its territories, except Vatican City, to the Kingdom of Italy.

The changes affected clergy and laypeople throughout Christendom, many of whom debated how the Church should be run and who had ultimate authority in the Church.

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Proponents of a conciliar approach argued that the pope could not make decisions without consulting the body of bishops. French Gallicanism, akin to conciliarism, minimized the pope’s authority over national churches and tied his teaching authority to the consent of the people. Secular leaders saw an advantage here because they could influence Rome by informing public opinion.

Others, clergy and laypeople alike, were weary of revolutions and looked to Rome to be a strong anchor amid stormy seas. Called “ultramontanists” because they looked “beyond the mountains” (the Alps) for guidance, they wanted the pope to assert his power in order to bring order to their homelands. A pope with supreme authority might calm the upheavals outside — and settle differences within — the Church.

Pope Pius IX noted guardedly the turbulence of the times, and he considered convening a council to address the situation as early as 1849. The way the world was headed, particularly the devaluation of religion, convinced him that the Church needed to clarify its teachings. After consulting the world’s bishops, Pius opened the First Vatican Council on Dec. 8, 1869. It halted abruptly on Oct. 20, 1870, after the Kingdom of Italy had seized papal Rome. Only two constitutions were issued by the council: Dei Filius (April 24, 1870) on faith and reason and Pastor Aeternus, which defined papal authority.


The text of Pastor Aeternus is amazingly brief — only four chapters and 38 paragraphs. The doctrine defined is equally concise: “the institution, permanence and nature of the sacred and apostolic primacy.” Still, the reader will find many supportive references to sacred Scripture, Tradition and Church councils. Indeed, it’s impossible to grasp adequately the meaning of Pastor Aeternus without seeing it in relation to Church life throughout the centuries.

Pastor Aeternus begins by affirming strongly the institution of apostolic primacy by Jesus, stating that he conferred “primacy of jurisdiction over the whole church of God” on Peter alone. The supporting biblical texts are John 1:42, Matthew 16:16-19 and John 21:15-17. In each of these, Jesus addresses Peter directly, charging him with leading the People of God.

Then Pastor Aeternus continues by declaring that Peter’s primacy of jurisdiction remains forever through the succession of popes. Jesus intended to establish a Church that stands until the end of time (cf. Mt 7:25; Lk 6:48). Permanence, therefore, marks the Petrine office instituted by Christ through the keys of the kingdom handed to Peter and, as Jesus intended, to “whoever succeeds to the chair of Peter.”

Regarding the nature of papal primacy, Pastor Aeternus turns to the teaching of the Council of Florence, which emphasized that the Roman pontiff governed the universal Church. This power is ordinary and immediate; the pope reigns over all other bishops and local churches. To exercise his authority, he does not need to appeal to anyone else, including civil authorities. All clergy and faithful should submit to the Roman pontiff in matters of faith and morals and the discipline and government of the Church, a submission civil authorities should respect.

The final chapter of Pastor Aeternus considers the Roman pontiff’s “supreme power of teaching,” including the concept of infallibility. While one might hear the opinion that infallibility is the main point of Pastor Aeternus, including it as one aspect of papal teaching authority and limiting its application to certain situations suggest that the Council Fathers, at least, saw it as secondary.

The pope’s teaching authority is rooted in Jesus’ choice of Peter as the Church’s solid foundation. Moreover, various councils — Fourth Council of Constantinople (869-870), Second Council of Lyons (1272-1274) and the Council of Florence (1431-1449) — noted consistently that the Faith received from Jesus has been preserved from error and defended from attacks through the judgments of the Holy See.

“For the Holy Spirit was promised to the successors of Peter not so that they might, by his revelation, make known some new doctrine, but that, by his assistance, they might religiously guard and faithfully expound the revelation or deposit of faith transmitted by the apostles.”

It is in service, then, to the pope’s teaching authority that infallibility is defined, a definition that, contrary to some popular notions, is quite circumscribed: “We teach and define as a divinely revealed dogma that when the Roman pontiff speaks ex cathedra, that is, when, in the exercise of his office as shepherd and teacher of all Christians, in virtue of his supreme apostolic authority, he defines a doctrine concerning the faith or morals to be held by the whole Church, he possesses, by the divine assistance promised to him in blessed Peter, that infallibility which the divine Redeemer willed his church to enjoy in defining doctrine concerning faith or morals. Therefore, such definitions of the Roman pontiff are of themselves, and not by the consent of the Church, irreformable.”

In modern times, the pope has called infallibility into play in defining the Immaculate Conception in 1854 (Ineffabilis Deus) and the Assumption of Mary in 1950 (Munificentissimus Deus). But a pope also is teaching infallibly when, as often happens, he reaffirms some doctrine or doctrines already clearly established as revealed truth and part of the Church’s faith.


Pastor Aeternus calls all members of the Church to obey the pope as chief shepherd and teacher — that is, when he speaks about faith and morals or the inner workings of the Church.

This may not seem like a momentous declaration, but considering that secular leaders then and now have wanted to control the Church — from appointing bishops to regulating doctrine — the content of Pastor Aeternus reminds the world that the state has limits to its power. In effect, the Church declares its independence from civil authority. A hundred years later, the Church builds upon Vatican I’s declarations at Vatican II, which upholds the right of individuals to believe and practice their faith as conscience dictates without interference by the state.

David Werning writes from Virginia.

Further reading

Ineffabilis Deus (Dec. 8, 1854): An apostolic constitution of Pope Pius IX which formally and authoritatively defines the immaculate conception of the Blessed Virgin Mary. It should be noted that the pope exercises the infallibility of the Petrine office with this declaration before the publishing of Pastor Aeternus.

Quanta Cura (Dec. 8, 1864): An encyclical by Pope Pius IX that condemns certain errors like secularism and religious indifferentism. It included an appendix, the Syllabus of Errors, which briefly describes 80 heresies.

Aeterni Patris (June 29, 1868): A pastoral letter from Pope Pius IX convoking the First Vatican Council. It gives as a reason for the council the hostility toward the Church but affirms the Church’s ability to overcome all opponents because of Jesus’ promise to be with the Church forever.

Dei Filius (April 24, 1870): The other constitution published by the First Vatican Council (the other being Pastor Aeternus), which defends the reasonableness of faith and the compatibility of faith and reason.

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