Use of term
The term "catholicism" is the
English form of
Late Latin catholicismus, an abstract noun based on the adjective
catholic. The Modern Greek equivalent
καθολικισμός (katholikismos) is back-formed and usually refers to
The Greek adjective
katholikos means "universal". Directly from the Greek, or via
Late Latin catholicus, the term catholic entered many other languages, becoming the base for the creation of various theological terms such as catholicism and catholicity (Late Latin catholicismus, catholicitas).
The use of the terms "catholicism" and "catholicity" is closely related to the use of
Catholic Church. The earliest evidence of the use of that term is the
Letter to the Smyrnaeans that
Ignatius of Antioch wrote in about 108 to Christians in
Smyrna. Exhorting Christians to remain closely united with their
bishop, he wrote: "Wherever the bishop shall appear, there let the multitude [of the people] also be; even as, wherever
Jesus Christ is, there is the Catholic Church."
From the second half of the second century, the word "catholic" began to be used to mean "orthodox" (non-heretical), "because Catholics claimed to teach the whole truth, and to represent the whole Church, while heresy arose out of the exaggeration of some one truth and was essentially partial and local".
 In 380, Emperor
Theodosius I limited use of the term "Catholic Christian" exclusively to those who followed the same faith as
Pope Damasus I of Rome and
Pope Peter of Alexandria.
 Numerous other early writers including
Cyril of Jerusalem (c. 315–386),
Augustine of Hippo (354–430) further developed the use of the term "catholic" in relation to Christianity.
In Christian theology, and specially in
ecclesiology, terms "Catholicism" and "Catholicity" are used in two basic forms, with capital "C" or just with small "c". When used with small "c", terms "catholicism" and "catholicity" generally designate theological doctrine of the "catholicity of the Church" without denominational connotations. On the other hand, when used with capital "C", terms "Catholicism" and "Catholicity" often designate a particular Christian denomination, depending on the personal views and theological positions of any particular author.
Catholics make up the single largest religion in the world with some 1.6 billion members. When combined with all
Christian faiths the total number of people swells to over 2 billion people as these faiths add over 500 million people. The
Muslim religion comes in second to Christians with about 1.5 billion people, of which about 1 billion are
Shia are about 250 million. Other Muslims faiths combine to make up the other 250 million people.
Summary of major divisions
A common belief in Catholicism is institutional continuity with the early Christian church founded by Jesus Christ. Many churches or communions of churches identify singularly or collectively as the authentic church. The following summarizes the major schisms and conflicts within Christianity, particularly within groups that identify as Catholic; there are several competing historical interpretations as to which groups entered into
schism with the original early church.
According to the theory of
Pentarchy, the early undivided church came to be organized under the three patriarchs of
Antioch, to which later were added the patriarchs of
Bishop of Rome was at that time recognized as first among them, as is stated, for instance, in canon 3 of the
First Council of Constantinople (381)—many interpret "first" as meaning here
first among equals—and doctrinal or procedural disputes were often referred to Rome, as when, on appeal by
Athanasius against the decision of the
Council of Tyre (335),
Pope Julius I, who spoke of such appeals as customary, annulled the action of that council and restored Athanasius and
Marcellus of Ancyra to their sees.
 The Bishop of Rome was also considered to have the right to convene ecumenical councils. When the Imperial capital moved to Constantinople, Rome's influence was sometimes challenged. Nonetheless, Rome claimed special authority because of its connection to
Saint Paul, who, all agreed, were martyred and buried in Rome, and because the Bishop of Rome saw himself as the successor of Saint Peter.
Council of Ephesus, the third
ecumenical council, was chiefly concerned with
Nestorianism, which emphasized the distinction between the humanity and divinity of Jesus and taught that, in giving birth to Jesus Christ, the Virgin Mary could not be spoken of as giving birth to God. This Council rejected Nestorianism and affirmed that, as humanity and divinity are inseparable in the one person of Jesus Christ, his mother, the Virgin Mary, is thus
Theotokos, God-bearer, Mother of God. The first great rupture in the Church followed this Council. Those who refused to accept the Council's ruling were largely
Persian and are represented today by the
Assyrian Church of the East and related Churches, which, however, do not now hold a "Nestorian" theology. They are often called Ancient Oriental Churches.
The next major break was after the
Council of Chalcedon (451). This Council repudiated
Eutychian Monophysitism which stated that the divine nature completely subsumed the human nature in Christ. This Council declared that Christ, though one person, exhibited two natures "without confusion, without change, without division, without separation" and thus is both fully God and fully human. The Alexandrian Church rejected the terms adopted by this Council, and the Christian Churches that follow the tradition of non-acceptance of the Council—they are not Monophysite in doctrine—are referred to as Pre-Chalcedonian or
Oriental Orthodox Churches.
The next great rift within Christianity was in the 11th century. Longstanding doctrinal disputes, as well as conflicts between methods of Church government, and the evolution of separate rites and practices, precipitated a split in 1054 that divided the Church, this time between a "West" and an "East".
Holy Roman Empire,
Baltic states, and Western Europe in general were in the Western camp, and
Russia and many other Slavic lands,
Anatolia, and the Christians in
Egypt who accepted the Council of Chalcedon made up the Eastern camp. This division between the
Western Church and the
Eastern Church is called the
In 1438, the
Council of Florence convened, which featured a strong dialogue focussed on understanding the theological differences between the East and West, with the hope of reuniting the Catholic and Orthodox churches.
 Several eastern churches reunited, constituting some of the
Eastern Catholic Churches.
Another major division in the Church occurred in the 16th century with the
Protestant Reformation, after which many parts of the
Western Church rejected Papal authority, and some of the teachings of the Western Church at that time, and became known as "
Reformed" or "
A much less extensive rupture occurred when, after the Roman Catholic Church's
First Vatican Council, in which it officially proclaimed the dogma of
papal infallibility, small clusters of Catholics in the Netherlands and in German-speaking countries formed the
Old-Catholic (Altkatholische) Church.