The doctrine of the infallibility of ecumenical councils states that solemn definitions of ecumenical councils, approved by the Pope, which concern faith or morals, and to which the whole Church must adhere, are infallible. Such decrees are often labeled as canons, and they often have an attached anathema, a penalty of excommunication, against those who refuse to believe the teaching. The doctrine does not claim that every aspect of every ecumenical council is infallible.
The Roman Catholic Church holds this doctrine, as do most or all Eastern Orthodox theologians. However, the Orthodox churches accept only the First seven Ecumenical Councils as genuinely ecumenical, while Roman Catholics accept twenty-one. Only a very few Protestants believe in the infallibility of ecumenical councils, and these usually restrict infallibility to the Christological statements of the first seven councils. Lutheran Christians recognize the first four councils, whereas most High Church Anglicans accept all seven as persuasive but not infallible.
The Greek Orthodox view accepts that an ecumenical council is itself infallible when pronouncing on a specific matter.
The Catholic Church teaches that Jesus Christ, "the Word made Flesh" (John 1:14), is the source of divine revelation. The Second Vatican Council states, "For this reason Jesus perfected revelation by fulfilling it through His whole work of making Himself present and manifesting Himself: through His words and deeds, His signs and wonders, but especially through His death and glorious resurrection from the dead and final sending of the Spirit of truth." (Dei verbum, 4). The content of Christ's divine revelation is called the deposit of faith, and is contained in both sacred scripture and sacred tradition, not as two sources but as a single source.
The magisterium (Latin: magister, "teacher") is the teaching office of the Catholic Church. Catholic theology divides the functions of the teaching office into two categories: the infallible sacred magisterium and the fallible ordinary magisterium. The infallible sacred magisterium includes the extraordinary declarations of the pope speaking ex cathedra and of ecumenical councils (traditionally expressed in conciliar creeds, canons, and decrees). Examples of infallible extraordinary papal definitions (and, hence, of teachings of the sacred magisterium) are Pope Pius IX's definition of the Immaculate Conception of Mary, and Pope Pius XII's definition of the Assumption of Mary. Before these definitions both sovereign pontiffs asked the bishops throughout the world whether these truths were indeed held by the faithful. Nowhere is it said that the Pope's charism involves special revelations, and the Pope must ascertain whether a belief is universally maintained before speaking ex cathedra on it. The above two instances of infallible definition outside an ecumenical council are the only two that can be cited in the history of the Catholic church.