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Now, every theologian agrees that if a pope becomes a manifest heretic, he ceases to be a member of the MBOC, and therefore, is not Pope. However, to be a heretic you must pertinaciously deny a fundamental truth of the Faith that must be believed in Faith (eg. The Resurrection, the Divinity of Christ). You must hold that belief in the face of correction. If a Pope holds a contrary view in secret, he may cease to be a member of the MBOC, but he does not lose his jurisdiction. If the secret becomes public, then a sentence must be pronounced. However, no one person can judge the Pope. They don’t have the authority. What would have to happen is that a group of authoritative members of the hierarchy make a declaratory (“it’s already happened”) sentence that the Pope’s manifest heresy has shown that he has placed himself outside of the Church. The consensus of canon law says that a General Council, or perhaps the cardinals, could make this statement. But not an individual layman.
Something else to remember, a pope is not bound by ecclesiastical law, only by divine law. Since the pope is the highest authority, he can dispense himself from any ecclesial law. For example, Pope Pius X loved snuff, and he would dispense himself from the fasting law before mass and chew snuff during Mass. He was completely entitled to it. Therefore, trying to nail a Pope for a latae sententiae excommunication by his violating canon law is irrelevant. He’s not bound by canon law. A Pope can merit censure, but it can only come from one of his successors. An individual may think the pope is individually asking him to do something immoral, and if he is absolutely convinced of this in his heart, he is bound not to do it. However, he cannot pass sentence on the Pope. This is why we must pray for the Pope.
The norms of the Church (not exceptions, conceded indults from the norm, etc….) that are imposed by the Church are protected by Christ’s promises. So, the official Missal of Paul VI contains nothing harmful or invalid because if it did, the church would have failed.
The logic of sedevacantism is self-refuting and hopeless. We should pray for their return to the fold.