Conciliarism was a reform 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, or even against, the pope. The movement emerged in response to the Great Western Schism between rival popes in Rome and Avignon. The schism inspired the summoning of the Council of Pisa (1409), which failed to end the schism, and the Council of Constance (1414–1418), which succeeded and proclaimed its own superiority over the Pope. Conciliarism reached its apex with the Council of Basel (1431–1449), which ultimately fell apart. The eventual victor in the conflict was the institution of the Papacy, confirmed by the condemnation of conciliarism at the Fifth Lateran Council, 1512–17. The final gesture however, the doctrine of Papal Infallibility, was not promulgated until the First Vatican Council of 1870.
The 13th and 14th centuries were a period of challenges to Papal authority in Catholic Europe. These new challenges were marked by disputes between the Papacy and the secular kings of Europe. In particular the quarrel between Philip IV of France and Pope Boniface VIII over the right to tax the clergy in France was especially heated. Philip was excommunicated and Boniface was accused of corruption, sorcery, and sodomy. In his "Unam Sanctam", Boniface asserted that the papacy held power over both the spiritual and temporal worlds and that only God could judge the pope. Philip responded by sending knights to Italy to arrest Boniface. Though the mission eventually failed, the Pope died just three weeks after his release because of the trauma of the experience and a high fever.
This was followed by the move of the Roman papacy to Avignon, France in 1305. Although the move had precedent, the Avignon Papacy's (1305–1377) image was damaged by accusations of corruption, favoritism toward the French, and even heresy. Indeed Pope Clement VI who was criticized for his apparent extravagant lifestyle asserted that his "predecessors did not know how to be Pope." During the span of the Avignon Papacy all the popes and most Cardinals and curial officials were French. The reputation of the Avignon Papacy led many to question the absolute authority of the pope in governing the universal Catholic Church.
The Western Schism (1378–1417), was a dispute between the legal elections of Pope Urban VI in Rome and Pope Clement VII in Avignon. The schism became highly politicized as the kings of Europe chose to support whichever pope served their best interests. Both popes chose successors and thus the schism continued even after Urban and Clement's deaths. In this crisis, conciliarism took center stage as the best option for deciding which pope would step down. The cardinals decided to convene the Council of Pisa (1409) to decide who would be the one pope of the Catholic Church. The council was a failure and even led to the election of a third pope. The Council of Constance (1414–1418) successfully ended the Schism by deposing two Popes (John XXIII and Benedict XIII) - the third Pope abdicated - and electing a successor in Martin V. The Council also decreed to maintain the council as the primary church body from then on, though Martin did not ratify this decision.
The papal curia's apparent inability to implement church reform resulted in the radicalisation of Conciliarism at the Council of Basel (1431–1449), which at first found great support in Europe but in the end fell apart. Parts sided with the Pope to form the Council of Florence, whereas the conciliar party in Basel elected another antipope before eventually losing its support among European governments.
At the convening of the Fifth Lateran Council (1512–1517), Pope Julius II reasserted the supremacy of papal authority over that of the councils. Populated by cardinals opposed to conciliarism, the Lateran Council condemned the authority of conciliary bodies. In fact, the council was an essential copy of the pre-Conciliar councils such as Lateran IV (1215), Lyon (1274), and Vienna (1311).
Conciliar theory 
William of Ockham (d. 1349) wrote some of the earliest documents outlining the basic understanding of conciliarism. His goal in these writing was removal of Pope John XXII, who had revoked a decree favoring Franciscan ideas about Christ and the apostles owning nothing individually or in common. Some of his arguments include that the election by the faithful, or their representatives, confers the position of pope and further limits the papal authority. The universal church is a congregation of the faithful, not the Roman Church, which was promised to the Apostles by Jesus. While the universal Church cannot fall into heresy, it is known that the Pope has fallen into heresy in the past. Should the pope fall into heresy a council can be convened without his permission to judge him. William even stated that because it is a "universal" church, that the councils should include the participation of lay men and even women.
In his Defensor Pacis (1324), Marsilius of Padua agreed with William of Ockham that the universal Church is a church of the faithful, not the priests. Marsilius focused on the idea that the inequality of the priesthood has no divine basis and that Jesus, not the pope, is the only head of the Catholic Church. Contradicting the idea of Papal infallibility, Marsilius claimed that only the universal church is infallible, not the pope. Marsilius differed from Ockham in his denial to the clergy of coercive power. Later conciliar theorists like Jacques Almain rejected Marsilius argument to that effect, preferring more traditional clericalism modified to be more constitutional and democratic in emphasis.
Conciliar theory has its roots and foundations in both history and theology, arguing that many of the most important decisions of the Catholic Church have been made through conciliar means, beginning with the First Council of Nicaea (325). Conciliarism also drew on corporate theories of the church, which allowed the head to be restrained or judged by the members when his actions threatened the welfare of the whole ecclesial body. The canonists and theologians who advocated conciliar superiority drew on the same sources used by Marsilius and Ockham, but they used them in a more conservative way. They wanted to unify, defend and reform the institution under clerical control, not advance a Franciscan or a lay agenda. Among the theorists of this more clerical conciliarism were Jean Gerson, Pierre d'Ailly and Francesco Zabarella. Nicholas of Cusa synthesized this strain of conciliarism, balancing hierarchy with consent and representation of the faithful.
Opposition to conciliarism 
Many members of the Church however, continued to believe that the pope, as the successor of Saint Peter, retained the supreme governing authority in the Church. Juan de Torquemada defended papal supremacy in his Summa de ecclesia, completed ca. 1453. A generation later, Thomas Cajetan vigorously defended Papal authority in his "On the comparison of the authority of pope and council". He wrote that "Peter alone had the vicariate of Jesus Christ and only he received the power of jurisdiction immediately from Christ in an ordinary way, so that the others (the Apostles) were to receive it from him in the ordinary course of the law and were subject to him." and that "it must be demonstrated that Christ gave the plenitude of ecclesiastical power not to the community of the Church but to a single person in it." Both writers represent the many cardinals, canon lawyers and theologians who opposed the conciliar movement and supported the supremacy of Peter's successors. Conciliarism did not disappear in the face of these polemics. It survived to endorse the Council of Trent which launched the Catholic Counter-Reformation in the 1540s and later appeared in the anti-curial polemics of Gallicanism, Josephinism and Febronianism.
Modern conciliarism 
Although Conciliarist strains of thought remain within the Church, particularly in the United States, Rome and the infallible sacred magisterium of the Roman Catholic Church holds that the Pope is the Vicar of Christ on earth, and has the authority to issue infallible statements. Recent examples of this Papal Infallibility being invoked include Pope Pius IX's 1854 definition of the dogma of the Immaculate Conception of Mary, and Pope Pius XII's 1950 definition of the dogma of the Assumption of Mary. The non-infallible teaching of the Second Vatican Council (which was a pastoral council as opposed to a council defining any doctrine or dogma) on the College of Bishops contained within the decree Lumen Gentium has sometimes been interpreted as conciliarism, or a least conducive to it, by heterodox and orthodox Catholics alike; however, the text of the document as well as an explanatory note (Nota Praevia) by Paul VI makes the distinction clear. There are Christians, especially of the Anglo-Catholic, Old Catholic and Eastern Orthodox communions, who maintain the absolute supremacy of an ecumenical council. See conciliarity; however, this belief, from the Eastern Orthodox view, has no historical connection with the above events in the history of the Western Church.
A new interest in conciliarism was awakened in Roman Catholic circles with the convocation of the Second Vatican Council. Heterodox writers like Hans Küng and Francis Christopher Oakley have argued that the decrees of the Council of Constance remain valid, limiting papal power, despite these decrees being opposed by all subsequent popes and ecumenical councils. The label "Conciliar Church" is used by many Catholics, traditionalist Catholics included, as a derogatory description of the Roman Catholic Church in light of the many misinterpretations and distortions of the decisions of Second Vatican Council, all in the name of the so-called "Spirit of the Council".
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