Sedevacantism

Sedevacantism is a viewpoint within traditionalist Catholicism that holds the papal see has been vacant since the death of Pope Pius XII in 1958, or at least since the death of Pope John XXIII in 1963. Adherents believe that the popes elected after Pope Pius XII were not true popes due to alleged heresy or apostasy, rendering their elections invalid.

The core of the sedevacantist argument rests on the interpretation of Canon Law and papal infallibility. They argue that if a pope falls into heresy, he automatically loses his office, even without a formal declaration from the Church. This is often referred to as the "material heresy" or "formal heresy" debate. Sedevacantists believe that the Second Vatican Council and the subsequent liturgical reforms introduced by the post-conciliar popes are evidence of this heresy.

Because they believe the papal see is vacant, sedevacantists do not recognize the authority of the popes elected since the mid-20th century. Consequently, they often reject the legitimacy of the Novus Ordo Missae (the Mass promulgated by Pope Paul VI) and adhere to the Tridentine Mass. They also generally refuse to recognize the validity of sacraments administered by clergy ordained under the new rites.

Different sedevacantist groups exist, with some consecrating their own bishops and ordaining their own priests, while others attend Mass celebrated by priests who are part of the sedevacantist movement but have not necessarily been ordained by bishops from within the movement. These groups are generally outside the visible communion of the Catholic Church as recognized by the Vatican.