infallibility (ĭnfălˌəbĭlˈətē) [key], in Christian thought, exemption from the possibility of error, bestowed on the church as a teaching authority, as a gift of the Holy Spirit. It has been believed since the earliest times to be guaranteed in such scriptural passages as John 14.16,17. The analogous attribute of the Bible is usually called inerrancy. Protestants widely reject infallibility of the church. The Orthodox Eastern Church holds that only the church, taken as an integral community and spiritual body guided by the Holy Spirit, is infallible. Roman Catholics hold that the infallibility of the church is vested in the pope, when he speaks ex cathedra (i.e., from the chair of Peter, as the visible head of the church) on matters of faith and morals. Definitive pronouncements resulting from an ecumenical council, when ratified by the pope, are also held to be infallible. The pope speaks ex cathedra only rarely and after long deliberation. The dogma of papal infallibility was enunciated by the First Vatican Council (1870).
See B. Tierney, Origins of Papal Infallibility, 1150–1350 (1972).