Sedevacantism is the position held by some people who identify as Catholic that the present occupier of the Holy See is not the pope due to the mainstream church's espousal of what they see as heresies of modernism and that, for lack of a valid pope, the See has been vacant since the death of Pope Pius XII in 1958, the death of Pope John XXIII in 1963, the death of Pope Paul VI in 1978, or since the first alleged publicly proclaimed heresy by Paul VI, etc.