There have been perhaps 30 or 40 Antipopes in the 2000-year history of the papacy.
An antipope is a person claiming to be Pope who was not duly elected or proclaimed
while a duly elected Pope was still in office.
To begin with, it is vital to understand that there is no power on earth which may
depose a Pope. Any duly elected Pope remains therefore in office until he dies or
resigns (as has happened just seven times). Anyone, therefore, who claims to be Pope
while a duly elected Pope is living and has not resigned is, ipso facto, an Antipope.
Papal election procedures are governed by the prescription of the last Pope who
provided for them (that is, any Pope can change them, but they remain in effect until
they are changed by a duly elected Pope).
During the first thousand years of the history of the Papacy the electors were the clergy
of Rome (priests and deacons); during the second thousand years we have had the
College of Cardinals.
But each Pope, having unlimited sovereign power as head of the Church, can prescribe
any method for the election of his successor(s) that he chooses. These methods must
then be followed in the next election after the death of the Pope who prescribed it, and
thereafter until they are changed. A Papal claimant not following these methods is also
an Antipope.
Since Antipopes by definition base their claims on defiance of proper Church authority,
all have been harmful to the Church, though a few have later reformed after giving up
their claims.
