Answer
The conciliar movement or conciliarism was a reform movement within the Catholic Church that promoted the idea that church councils have authority over popes.
One of the keystones of Protestant theology is that each person has the right and responsibility to interpret the Bible for himself. This does not mean that every individual interpretation is correct—far from it. However, it does establish the principle that the individual is responsible to read and study the Bible for himself rather than accepting the word of an established authority. While teachers and leaders within the church are to challenge error and thus protect the flock, it is the individual who, in the final analysis, will be right or wrong before God. Roman Catholics often fault Protestants on their lack of a final authority on matters of biblical interpretation.
The conciliar movement exists because Roman Catholics accept several streams of authority—the Bible, church tradition, church councils and the pope. While the Bible is accepted as an authority, the church tells its members what the proper interpretation of the Bible is. So, who decides which interpretation of Scripture or which church tradition is authoritative? The answer is either the popes or the church councils or both. Although the official doctrine of the infallibility of the pope was not adopted until the First Vatican Council (1869–1870), the pope’s authority had been recognized for a long time, and many popes claimed to have supreme authority in the church. (The infallibility of the pope does not mean that he is infallible in everything that he says or does; rather, that when he is speaking ex cathedra—sitting on the throne of St. Peter and making a pronouncement that is meant to be binding for the entire Catholic Church—his pronouncement will in fact be the infallible rule for the church.)
In the 16th century, when Martin Luther was confronted with the authority of the church and ordered to recant, he stated his position clearly, and his answer reveals the primary difference between the Catholic view of authority and what came to be the Protestant view: “Unless I am convinced by the testimony of the Holy Scriptures or by evident reason—for I can believe neither pope nor councils alone, as it is clear that they have erred repeatedly and contradicted themselves—I consider myself convicted by the testimony of Holy Scripture, which is my basis; my conscience is captive to the Word of God. Thus I cannot and will not recant, because acting against one’s conscience is neither safe nor sound. God help me.”
Many Protestants do look to early church councils (like Nicea) as being authoritative—but only in that these councils arrived at decisions that are clearly supported by Scripture. Protestants feel obligated to disagree with councils that reach conclusions not supported by Scripture.
In 13th and 14th centuries, the papacy seemed to be especially corrupt and also in conflict with the secular rulers in Europe. The papal headquarters was moved to Avignon, France, in 1309. There, Clement VII was elected pope by primarily French cardinals. A rival, Urban VI, was elected pope in Rome. It was these disputed elections that led to the beginning of the conciliar movement. The leaders of Europe aligned themselves with one or the other of the two popes. Each pope was succeeded by a replacement upon his death, so the controversy continued. In order to try to settle the issue, the cardinals convened the Council of Pisa (1409). Instead of choosing between the existing popes, they elected a third, which only compounded the problem as now three men claimed the title.
The Council of Constance (1414–1418) deposed two of the existing popes (the third abdicated) and elected Martin V as the sole pope. That council also decided that church councils would have authority over the popes. However, Martin V refused to ratify their decision. In protest, the conciliarists eventually held the Council of Basel (1430–1449) to try to gain control over the pope, but their attempt failed. From this council came the Council of Florence, which elected an (anti)pope who was favorable to conciliarism. However, conciliarism did not find support among the secular leaders of Europe and eventually collapsed.
The Fifth Lateran Council (1512–1517) was opposed to conciliarism and reasserted the primacy of the pope. Today, the pope is considered the supreme authority within the Catholic Church, although there are still some who support conciliarism, especially in the United States.