Sedevacantism () is a doctrinal position within traditionalist Catholicism, which holds that the present occupier of the Holy See is not a valid pope due to the Pope's espousal of one or more heresies and that, for lack of a valid pope, the See of Rome is vacant. The term sedevacantism is derived from the Latin phrase sede vacante, which means "with the chair [i.e. of the Bishop of Rome] being vacant". The phrase is commonly used to refer specifically to a vacancy of the Holy See from the Pope's death or resignation, to the election of his successor. Among sedevacantists, some chose to end the vacancy in the Holy See by electing their own pope; hence, they are more appropriately called conclavists. The number of sedevacantists is unknown and difficult to measure; estimates range from tens of thousands to hundreds of thousands. Positions Origin Sedevacantism owes its origins to the rejection of the theological and disciplinary changes implemented following the Second Vatican Council (1962–65). Sedevacantists reject this Council, on the basis of their interpretation of its documents on ecumenism and religious liberty, among others, which they see as contradicting the traditional teachings of the Catholic Church and as denying the unique mission of Catholicism as the one true religion, outside of which there is no salvation. They also say that new disciplinary norms, such as the Mass of Paul VI, promulgated on 3 April 1969, undermine or conflict with the historical Catholic faith and are deemed blasphemous, while post-Vatican II teachings, particularly those related to ecumenism, are labelled heresies. They conclude, on the basis of their rejection of the revised Mass rite and of postconciliar church teaching as false, that the popes involved are also false. Among even traditionalist Catholics, this is a quite divisive question. Traditionalist Catholics other than sedevacantists recognize as legitimate the line of popes leading to and including Pope Francis. Sedevacantists, however, claim that the infallible Magisterium of the Catholic Church could not have decreed the changes made in the name of the Second Vatican Council, and conclude that those who issued these changes could not have been acting with the authority of the Catholic Church. Accordingly, they hold that Pope John XXIII and his successors left the true Catholic Church and thus lost legitimate authority in the church. A formal heretic, they say, cannot be the Catholic pope. Justification While Sedevacantists' arguments often hinge