You need a statement like, "All Bishops with ordinary jurisdiction can defect, so long as some vagrant clerics without jurisdiction remain". Do you have anything like that?
1. All V2 bishops with oridinary jurisdiction have not defected, +Vigano being a good example, and maybe others like +Schneider and +Sarah, to a smaller degree.
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2. During Arianism, most clerics defected (I cannot say all, but I also cannot say that some didn't, as history does not concern itself with such details). What we know is that +Athanasius did not defect, even though he was stripped of ordinary jurisdiction, being the equivalent of a current "Trad bishop", such as +Williamson or +Sanborn, +Dolan, etc..
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The home aloners who make the jurisdiction argument are taking 60 year sedevacantism to its logical conclusion. They are pointing out there are no authorized sede Priests or authorized sede Bishops since there was no Pope to authorize them.
And they are wrong, because canon law authorizes jurisdiction in emergency circuмstances, such as happened during china's communistic reign, when chinese bishops ordained/consecrated bishops for the preservation of the faith, unknown to Rome.
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I'm not disagreeing with the conclusion of their argument. I'm disagreeing with the premise that led to that conclusion. If and only if there was no Pope, it's true that no one was authorized these last 60 years.
Pope or no pope, "home aloners" are wrong (just as you are) because you restrict canon law (i.e. church law) to papal authority. The Church is greater than the pope because Christ created the papacy. The pope exists to teach/govern the Church; the Church does is not restricted by a pope or a lack his leadership.
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I can show you sources that Ordinary Jurisdiction only passes to Bishops through the Successor of St. Peter.
Canon Law = supplied jurisdiction for many cases.
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To say a heretic can serve as a conduit for authority to be transmitted to Catholics is absurd.
Whether a heretical pope can or can't provide jurisdiction is irrelevant. Canon law allows for supplied jurisdiction, to those faithful who request the sacraments, either way.
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There is such a thing as a materially heretic pope (not yet declared, not yet decided he is obstinate) who is not yet a formal heretic. So, in such cases, the church still continues to operate, whether or not the pope is a heretic or not.
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I only said two things were heresy (1) Ecclesia-Vacantism, or no hierarchy. (2) Indefinite SVism, or the idea that a vacancy can be extended forever unproblematically.
1) As during Arianism, where was the hierarchy? It was in St Athanasius (excommunicated, with no ordinary jurisdiction) and others like him. He was not, legally, the hierarchy, so according to your definition, during Arianism, there was no hierarchy, bu the Church still survived.
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2) No one says that SVism extends indefinitely. We just haven't seen the end of it. All signs, including many prophecies, point to a miraculous resurrection of the Church. Svism doesn't have to explain the full theory to be correct. Its principles are solid.