In chapter XXI of his book called "Open letter to confused Catholics," (published in 1986) Archbishop Lefebvre wrote:
"I have not ceased repeating that if anyone separates himself from the Pope, it will not be I. The question comes down to this: the power of the Pope within the Church is supreme, but not absolute and limitless, because it is subordinate to the Divine authority which is expressed in Tradition, Holy Scripture, and the definitions already promulgated by the Church's magisterium. In fact, the limits of papal power are set by the ends by which it was given to Christ's Vicar on earth, ends which Pius IX clearly defined in the Constitution 'Pastor Aeternus.' of the First Vatican Council. So in saying this, I am not expressing a personal theory.
"Blind obedience is not Catholic; nobody is exempt from responsibility from having obeyed man rather than God if he accepts orders from a higher authority, even if the Pope, when these are contrary to the Will of God as it is known with certainty from Tradition. It is true that one cannot envisage such an eventuality when the papal infallibility is engaged; but this happens only in a limited number of cases. It is an error to think that every word uttered by the Pope is infallible.
"Nevertheless, I am not among those who insist or insinuate that Paul VI was a heretic and therefore, by that very fact, no longer Pope. John Paul I and John Paul II would not have been legitimately elected. This is the position of the so-called "sede-vacantists."
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Archbishop Lefebvre lived another five years after the book was published. It's obvious that he was NOT a sedevacantist.