The Sede position of the Chair being empty, is it in a spiritual sense or a physical sense? Or both?
The sedevacantist position is that the chair of Peter is vacant; that it is currently not occupied and that it has not been occupied since 1958.
The sedevacantist believes this based on a hypothetical dialog St. Bellarmine entered into on the possibility of the Catholic Church having an heretical pope. St. Bellarmine, like St. Alphonsus, believed the position possible in theory but impossible in practice.
Great Churchmen have debated the possibility of an heretical pope for centuries. The subject was even brought up in several general councils. Further discussion about the issue was abandoned because it can not happen in practice...only in theory...and it was this theoretical discussion St. Bellarmine entered into. An example of the sedevacantist theory is well illustrated as follows:
A man can run one mile in 4 minutes. It is 2,500 miles from New York to Los Angelus. If the man starts in New York he will be in LA in:
(2,500 miles x 4 minutes) / (60 minutes x 24 hours) = 6.94 days !!
In theory...a man can make this run...but in practice it will never happen.
The sedevacantist bases his rejection of the last 4 popes on the above theory...that a man can run from New York to LA in 6.94 days. The sedevacantist refuses to see the difference between the theoretical and the actual reality. They would rather be wrong for sake of argument and the fracturing of the Church than to expand their minds into accepting the truth, because it requires eating a rather large piece of humble pie.
The Dominican theologian, Melchior Cano (1509-1560) taught explicitly what had been admitted implicitly...that the Church is infallible in the laws which it establishes for all Christian people. He did, however, recognize that that these laws can lack prudence and balance. He made particular mention to the laws of ecclesiastical penalties, censures, excommunications, suspensions, irregularities, and interdicts, but insisted that EVERYTHING in the precepts, decisions, and sanctions of the pope and councils that contributes fully to the life of the faithful is the object of infallibility of the Church in the sense that the Church can command nothing contrary to the Doctrine of Christ or the precepts of reason. (M. Cano, De Locis Theologicis, vol 5, page 138.) This is the same opinion St. Bellarmine held who declared it impossible for the pope to err "in precepts addressed to the entire Church" and "concerning things necessary for salvation". (R. Bellarmine, De Romano Pontifice, vol. 4, chapter 5).
What actually happened was the Vatican II dictates were "so close" to being heretical that all it took was the deliberate or willful mis-interpretation of the local bishops to complete the damage being done. In this way, all involved could say "they did nothing wrong" when in fact they did. Rome erred in making policy that was twisted and impossible to hold...the local bishops failed to question and protect. Consider this analogy:
A cook places poison in an identical salt shaker then places it next to the other shaker in the cabinet. When the maid comes into the kitchen she places both on the table...unaware. Is there a law that says the cook can not put poison in a salt shaker? No...but we can see that the cook's doing so is intending to hope that the maid is not diligent in her duty in recognizing the danger....then serving the poison with the salt.
That the Vatican II documents are like this we will not deny. This, then, is the legal loop hole used. The documents are both orthodox and hetrodox...thus the confusion and the argument that the Church does not err rather the men that hold lofty positions.
The sedevacantist is, at heart, well intended, but they do greater damage than they will admit. Here is wisdom: Beware someone who is a fanatic about... anything.