Concerning the deposition of a heretical Pope, the Traditional Dominicans of Avrillé in France have done us a great favour by publishing not only the classic considerations of John of St Thomas (cf. EC 405), but also those of other outstanding theologians. In brief, the best minds of the Church teach that a simple and popular argument today, namely that a heretical Pope cannot be a member of the Church and therefore all the less its head, is a little too simple. In brief, there is more to the Pope than just the individual Catholic who by falling into heresy loses the faith and with it his membership of the Church. For the Church, the Pope is much more than just an individual Catholic.
For clarity, let us present these theologians’ arguments in the form of question and answer:—
First of all, is it possible for a Pope to fall into heresy?
If he engages all four conditions of his Extraordinary Magisterium, he cannot teach heresy, but that he can personally fall into heresy is the more probable opinion at least of older theologians.
Then if he does fall into heresy, does that not make him cease to be a member of the Church?
As an individual Catholic person, yes, but as Pope, not necessarily, because the Pope is much more than just an individual Catholic. As Augustine said, the priest is Catholic for himself, but he is priest for others. The Pope is Pope for the entire Church.
But supposing that the great majority of Catholics can see that he is a heretic, because it is obvious. Would not his heresy in that case make it impossible for him to be Pope any longer?
No, because even if his heresy were obvious, still many Catholics might deny it, for instance out of “piety” towards the Pope, and therefore to prevent confusion from arising throughout the Church, an official declaration of the Pope’s heresy would be necessary to bind Catholics to stay united. Such a declaration would have to come from a Church Council, assembled for that purpose.
But if the heresy were public and obvious, surely that would be enough to depose him?
No, because firstly every heretic must be officially warned before being deposed, in case he would retract his heresy. And secondly, in Church or State every high official is serving the common good, and for the common good he must stay in office until he is officially deposed. So just as a bishop stays in office until he is deposed by the Pope, so the Pope stays in office until the official declaration of his heresy by a Church Council enables Christ to depose him (cf. EC 405).
But if a heretic is not a member of the Church, how can he be its head, the most important member?
Because his personal membership is a different thing from his official headship. By his personal membership he receives sanctification from the Church. By his official headship he gives official government to the Church. So by falling into heresy, he ceases to be a living member of the Church, that is true, but he does not thereby cease being able, even as a dead member, to govern the Church. His membership of the Church by faith and charity is incompatible with heresy, but his governing of the Church by his official jurisdiction, not requiring faith or charity, is compatible with heresy.
But by his heresy a former Pope has thrown away his Papacy!
Personally and in private that is true, but that is not true officially and in public until a Church Council has made not only public but also official his heresy. Until then the Pope must be treated as Pope, because for the Church’s tranquillity and common good, Christ maintains his jurisdiction.