I personally think Ladislaus' position, though I don't agree with it entirely, is a quite reasonable one. It is universally taught a doubtful Pope, a doubtful law, a doubtful command cannot oblige one's conscience, if there are solid and objective foundations for this doubt. Some theologians think all Popes during the Great Schism were doubtful, hence there would have been no sin or schism in choosing one or the other, or even being personally suspicious of all, so long as one was ready to submit to any after his uncontested acceptance became an indisputable fact. As a matter of fact, according to John of St. Thomas and several others, if a universally accepted Papal election has not been completed, the election is regarded as
still going on, and the Church has it in Her power to do whatever is necessary to allay the remaining doubts and bring the matter to a conclusion. But that brings us back to , after a universally accepted election is manifest, all theologians teach that such doubts can no longer remain.
I would ask Ladislaus, supposing it is true that the See is vacant, then that doubt could be resolved by a later judgment of the Church, so that all may have infallible certainty after that.
But what if the See was not vacant? What set of necessary and sufficient conditions would prove this, with the same infallible certainty, according to you? There must be some set of such conditions, otherwise the matter could not be resolved. If you consider this question, I think you'll see the answer, and only answer, can be the acceptance of the Church, the universal episcopate in particular.
The Church has the right to elect the Pope, and therefore the right to certain knowledge as to who is elected. As long as any doubt remains and the tacit consent of the universal Church has not yet remedied the possible flaws in the election, there is no Pope, papa dubius, papa nullus. As a matter of fact, remarks John of St. Thomas, in so far as a peaceful and certain election is not apparent, the election is regarded as still going on. And since the Church has full control, not over a Pope certainly elected, but over the election itself, she can take all measures needed to bring it to a conclusion. The Church can therefore judge a Pope to be doubtful. Thus, says John of St. Thomas, the Council of Constance judged three Popes to be doubtful, of whom two were deposed, and the third renounced the pontificate (loc. cit., a. 3, nos. 10-11; vol. VII, p. 254) ...
But the peaceful acceptance of the universal Church given to an elect as to a head to whom it submits is an act in which the Church engages herself and her fate. It is therefore an act in itself infallible and is immediately recognizable as such. (Consequently, and mediately, it will appear that all conditions prerequisite to the validity of the election have been fulfilled.
Acceptance by the Church operates either negatively, when the election is not at once contested; or positively, when the election is first accepted by those present and then gradually by the rest (cf. John of St. Thomas, II-II, qq. 1-7; disp. 2, a. 2, nos. 1, 15, 28, 34, 40; pp. 228 et seq. ).
God can permit that at times a vacancy in the Apostolic See be prolonged for a long time. He can also permit that doubt arise about the legitimacy of this or that election. He cannot however permit that the whole Church accept as Pontiff him who is not so truly and legitimately ... Let this be said in passing against those who, trying to justify certain attempts at schism made in the time of Alexander VI, allege that its promoter broadcast that he had most certain proofs, which he would reveal to a General Council, of the heresy of Alexander. Putting aside here other reasons with which one could easily be able to refute such an opinion, it is enough to remember this: it is certain that when Savonarola was writing his letters to the Princes, all of Christendom adhered to Alexander VI and obeyed him as the true Pontiff. For this very reason, Alexander VI was not a false Pope, but a legitimate one. Therefore he was not a heretic ...