Modernism in the Catholic Church in the context of "Pope Pius X"

The First Ecumenical Council of the Vatican, commonly known as the First Vatican Council or Vatican I, was the 20th ecumenical council of the Catholic Church, held three centuries after the preceding Council of Trent which was adjourned in 1563. The council was convoked by Pope Pius IX on 29 June 1868, under the rising threat of the Kingdom of Italy encroaching on the Papal States. It opened on 8 December 1869 and was adjourned on 20 September 1870 after the Italian Capture of Rome. Its best-known decision is its definition of papal infallibility.

The council's main purpose was to clarify Catholic doctrine in response to the rising influence of the modern philosophical trends of the 19th century. In the Dogmatic Constitution on the Catholic Faith (Dei Filius), the council condemned what it considered the errors of rationalism, anarchism, communism, socialism, liberalism, materialism, modernism, naturalism, pantheism, and secularism.

Liberal Catholicism is a current of thought within the Catholic Church influenced by classical liberalism and promoting the separation of church and state, freedom of religion in the civic arena, expanded suffrage, and broad-based education. It was influential in the 19th century and the first half of the 20th, especially in France. It is largely identified with French political theorists such as Felicité Robert de Lamennais, Henri Lacordaire, and Charles Forbes René de Montalembert influenced, in part, by a similar contemporaneous movement in Belgium.

Being predominantly political in nature, liberal Catholicism as a movement was distinct from the contemporary theological movement of modernism. The movement is also distinct from the attitude of historical and present-day Roman Catholics who are described as theologically progressive or liberal.

Conservative Christianity, also known as conservative theology, theological conservatism, traditional Christianity, or biblical orthodoxy is a grouping of overlapping and denominationally diverse theological movements within Christianity that seeks to retain the orthodox and long-standing traditions and beliefs of Christianity. It is contrasted with Liberal Christianity and Progressive Christianity, which are seen as heretical heterodoxies by theological conservatives. Conservative Christianity should not be mistaken as being necessarily synonymous with the political philosophy of conservatism, nor the Christian right (which is a political movement of Christians who support conservative political ideologies and policies within the realm of secular or non-sectarian politics).

Theological conservatism is found in Roman Catholicism, Eastern Orthodoxy, Oriental Orthodoxy, Protestantism, the Church of the East, Old Catholicism, and throughout all of Mainstream-Nicene Christianity in both Western Christian and Eastern Christian traditions. Within Protestantism, it is largely made up of Evangelical Christianity and Christian Fundamentalism, while the Confessing Movement, Confessionalism, and to an extent Neo-orthodoxy make up the remaining; in Roman Catholicism it is inclusive of Catholics that adhere to Traditionalist Catholicism as well as the Magisterium, Scriptures, and Traditions of the Church at the exclusion of Catholic Modernism and Folk Catholicism; and in Old Catholicism it currently includes the Union of Scranton, those of similar beliefs, and historically the Union of Utrecht until its adoption of theological liberalism. In spite of this, not every community has had a direct connection with the Fundamentalist–Modernist controversy.