"Given that, as a private person, the
Pontiff could indeed become a public, notorious, and obstinate heretic … he
would fall by the very fact of heresy from his papal power, in so far as he
would have been removed from within the Church’s body on his own accord by
having become an unbeliever. In that case, only
a Council [the Church] would have the right to declare his see vacant so
that the usual electors could safely proceed to an election." ( Hervé. Manuale Theologiae Dogmaticae (1952) I.500, p. 495