You learn something new every day
An LJ friend, this morning, introduced me a to a new concept: sedevacantism. Sedevacantists believe that the papacy has been vacant since the death of Pope Pius XII in 1958 (or, in some cases, the death of Pope John XXIII in 1963). Sedevacantists believe that the subsequent successors (or, in their view, claimants) to the papal office have been neither true Catholics nor true, legitimate popes. Tell that to John Paul II and those who either want to canonize him or want to add the epithet "the Great" to his title. The Wikipedia entry I linked to above goes into the history of this position. Fascinating stuff.