First Vatican Council in the context of Secularism

Papal supremacy is the doctrine of the Catholic Church that the pope, by reason of his office as vicar of Christ, the visible source and foundation of the unity both of the bishops and of the whole company of the faithful, and as priest of the entire Catholic Church, has full, supreme, and universal power over the whole church, a power which he can always exercise unhindered: that, in brief, "the pope enjoys, by divine institution, supreme, full, immediate, and universal power in the care of souls."

The doctrine had the most significance in the relationship between the church and the temporal state, in matters such as ecclesiastic privileges, the actions of monarchs and even successions.

The Union of Utrecht of the Old Catholic Churches, most commonly referred to by the short form Union of Utrecht (UU), is a federation of Old Catholic churches, nationally organized from schisms which rejected Roman Catholic doctrines of the First Vatican Council in 1870; its member churches are not in communion with the Roman Catholic Church.

The 1889 Declaration of Utrecht is one of three founding documents together called the Convention of Utrecht. Many provinces of the Union of Utrecht of the Old Catholic Churches are members of the World Council of Churches. The UU is in full communion with the Evangelical Lutheran Church of Sweden; the Anglican Communion through the 1931 Bonn Agreement; the Philippine Independent Church, the Spanish Reformed Episcopal Church, and the Lusitanian Catholic Apostolic Evangelical Church through a 1965 extension of the Bonn Agreement; and, the Mar Thoma Syrian Church through the 2024 Thiruvalla agreement.

The terms Old Catholic Church, Old Catholics, Old-Catholic churches, or Old Catholic movement, designate "any of the groups of Western Christians who believe themselves to maintain in complete loyalty the doctrine and traditions of the undivided church but who separated from the See of Rome after the First Vatican Council of 1869–70".

The expression Old Catholic has been used from the 1850s by communions separated from the Roman Catholic Church over certain doctrines, primarily concerned with papal authority and infallibility. Some of these groups, especially in the Netherlands, had already existed long before the term. The Old Catholic Church is separate and distinct from Traditionalist Catholicism.

Deiparae Virginis Mariae (Latin for "Virgin Mary Mother of God"), is an encyclical of Pope Pius XII released on May 1, 1946 addressed to all Catholic bishops on the possibility of defining the Assumption of the Blessed Virgin Mary as a dogma of faith.

The encyclical states that for a long time numerous petitions have been received from cardinals, patriarchs, archbishops, bishops, priests, religious of both sexes, associations, universities and innumerable private persons, all begging that the bodily Assumption into heaven of the Blessed Virgin should be defined and proclaimed as a dogma of faith. This was also fervently requested by almost two hundred fathers in the Vatican Council (1869–1870).

The 19th century began on 1 January 1801 (represented by the Roman numerals MDCCCI), and ended on 31 December 1900 (MCM). It was the 9th century of the 2nd millennium. It was characterized by vast social upheaval. Slavery was abolished in much of Europe and the Americas. The First Industrial Revolution, though it began in the late 18th century, expanded beyond its British homeland for the first time during the 19th century, particularly remaking the economies and societies of the Low Countries, France, the Rhineland, Northern Italy, and the Northeastern United States. A few decades later, the Second Industrial Revolution led to ever more massive urbanization and much higher levels of productivity, profit, and prosperity, a pattern that continued into the 20th century. The Catholic Church, in response to the growing influence and power of modernism, secularism and materialism, formed the First Vatican Council in the late 19th century to deal with such problems and confirm certain Catholic doctrines as dogma. Religious missionaries were sent from the Americas and Europe to Asia, Africa and the Middle East.

In the Middle East, it was an era of change and reform. The Islamic gunpowder empires fell into decline and European imperialism brought much of South Asia, Southeast Asia, and almost all of Africa under colonial rule. Reformers were opposed at every turn by conservatives who strove to maintain the centuries-old Islamic laws and social order. The 19th century also saw the collapse of the large Spanish, Portuguese, French and Mughal empires, which paved the way for the growing influence of the British, French, German, Russian, Austro-Hungarian, Italian, and Japanese empires along with the United States.

Pope Pius IX (Italian: Pio IX; born Giovanni Maria Battista Pietro Pellegrino Isidoro Mastai-Ferretti; 13 May 1792 – 7 February 1878) was head of the Catholic Church from 1846 to 1878. His reign of nearly 32 years is the longest verified of any pope in history and second only to Saint Peter according to Catholic tradition. He was notable for convoking the First Vatican Council in 1868 which defined the dogma of papal infallibility before taking a break in summer of 1870. The council never reconvened. At the same time, France started the French-Prussian War and removed the troops that protected the Papal States, which allowed the Capture of Rome by the Kingdom of Italy on 20 September 1870. Thereafter, he refused to leave Vatican City, declaring himself a "prisoner in the Vatican".

At the time of his election, he was a liberal reformer, and during his early papacy, he enacted progressive reforms, but his approach changed after the Revolutions of 1848. When his prime minister, Pellegrino Rossi, was assassinated and Pius himself was made prisoner in his own palace, he fled Rome and excommunicated all participants in the short-lived Roman Republic. After its suppression by the French army and his return in 1850, his policies and doctrinal pronouncements became increasingly conservative. He was responsible for the kidnapping of Edgardo Mortara, a six-year-old taken by force from his Jewish family who went on to become a Catholic priest in his own right and unsuccessfully attempted to convert his Jewish parents.

Papal infallibility is a dogma of the Catholic Church (both the Latin and Eastern Catholic churches) which states that, in virtue of the promise of Jesus to Peter, the Pope when he speaks ex cathedra is preserved from the possibility of error on doctrine "initially given to the apostolic Church and handed down in Scripture and tradition". It does not mean that the pope cannot sin or otherwise err in many cases. This doctrine, defined dogmatically at the First Vatican Council of 1869–1870 in the document Pastor aeternus, is claimed to have existed in medieval theology and to have been the majority opinion at the time of the Counter-Reformation.

The doctrine of infallibility relies on one of the cornerstones of Catholic dogma, that of papal supremacy, whereby the authority of the pope is the ruling agent as to what are accepted as formal beliefs in the Catholic Church. The use of this power is referred to as speaking ex cathedra. "Any doctrine 'of faith or morals' issued by the pope in his capacity as successor to St. Peter, speaking as pastor and teacher of the Church Universal [Ecclesia Catholica], from the seat of his episcopal authority in Rome, and meant to be believed 'by the universal church,' has the special status of an ex cathedra statement. Vatican Council I in 1870 declared that any such ex cathedra doctrines have the character of infallibility (session 4, Constitution on the Church 4)."

Conciliarism was a movement in the 14th-, 15th- and 16th-century Catholic Church which held that supreme authority in the Church resided with an ecumenical council, apart from, despite, or even if opposed by, the pope.

The movement emerged in response to the Western Schism between rival popes in Rome and Avignon. It was proposed that both popes abdicate in order to allow a new election that implemented a proposal where government supporters of the popes withdraw allegiance and thus prepare the way for a new election. The schism led to the summoning of the Council of Pisa (1409), which failed to end the schism, and the Council of Constance (1414–1418), which had more success, but which also proclaimed its own superiority over the Pope. Conciliarism reached its apex with the Council of Basel (1431–1449). The eventual victor in the warring movements was the pope and the institution of the papacy: the pope's power and teaching authority was confirmed by the condemnation of conciliarism at the Fifth Lateran Council (1512–1517). The apex of the theory of papal authority, on the other hand, was probably reached with the adoption of the doctrine of papal infallibility, promulgated (ironically) by the First Vatican Council (1870).

Munificentissimus Deus (Latin: The most bountiful God) is an apostolic constitution published in 1950 by Pope Pius XII. It defines ex cathedra the dogma of the Assumption of the Blessed Virgin Mary. It was the first and thus far the only ex-cathedra infallible statement since the official ruling on papal infallibility was made at the First Vatican Council (1869–1870). In 1854 Pope Pius IX had made an infallible statement with Ineffabilis Deus on the Immaculate Conception of the Virgin Mary, which was a basis for this dogma.

Pastor aeternus ("First Dogmatic Constitution on the Church of Christ") was issued by the First Vatican Council, July 18, 1870. The document defines four doctrines of the Catholic faith: the apostolic primacy conferred on Peter, the perpetuity of the Petrine Primacy in the Roman pontiffs, the definition of the papal primacy as a papal supremacy, and Papal infallibility – infallible teaching authority (magisterium) of the Pope.

Johannes Baptist Franzelin (15 April 1816 – 11 December 1886) was an Austrian Jesuit theologian and Cardinal. A papal theologian at the First Vatican Council, he assisted with drafting the Apostolic Constitutions composed during the council.

The Porvoo Communion is a communion of 15 predominantly northern European Anglican and Evangelical Lutheran churches, with some church bodies in the Iberian Peninsula of the same denomination. It was established in 1992 by a theological agreement entitled the Porvoo Common Statement which establishes full communion between and among these churches. The agreement was negotiated in the town of Järvenpää in Finland, but the communion's name comes from the nearby city of Porvoo, where a joint Eucharist (or Holy Communion) was celebrated in Porvoo Cathedral after the formal signing in Järvenpää. The Porvoo Communion claims to represent 45 million members among the member churches, approximately 50% of Europe's Protestants.

Dei Filius is the incipit of the dogmatic constitution of the First Vatican Council on the Catholic faith, which was adopted unanimously, and issued by Pope Pius IX on 24 April 1870.

The constitution set forth the teaching of "the holy Catholic Apostolic Roman Church" on God, revelation and faith.

Papal infallibility is a dogma of the Catholic Church which states that, in virtue of the promise of Jesus to Peter, the Pope when he speaks ex cathedra is preserved from the possibility of error on doctrine "initially given to the apostolic Church and handed down in Scripture and tradition". It does not mean that the pope cannot sin or otherwise err. This doctrine, defined dogmatically at the First Vatican Council of 1869–1870 in the document Pastor aeternus, is claimed to have existed in medieval theology and to have been the majority opinion at the time of the Counter-Reformation.

The doctrine of infallibility relies on one of the cornerstones of Catholic dogma, that of papal supremacy, whereby the authority of the pope is the ruling agent as to what are accepted as formal beliefs in the Catholic Church. The use of this power is referred to as speaking ex cathedra. "Any doctrine 'of faith or morals' issued by the pope in his capacity as successor to St. Peter, speaking as pastor and teacher of the Church Universal [Ecclesia Catholica], from the seat of his episcopal authority in Rome, and meant to be believed 'by the universal church,' has the special status of an ex cathedra statement. Vatican Council I in 1870 declared that any such ex cathedra doctrines have the character of infallibility (session 4, Constitution on the Church 4)."