Expert: Fr. Michael - 12/15/2009

Question
Father, in terms of the infallibility of apostolic succession and the guidance of the Holy Ghost, is it ever possible for the seat of St. Peter to be filled ( past, present and future )by a full blown heretic?

Answer
There is no such concept as "infallibility of apostolic succession."  You are probably misunderstanding the concept of the so-called extraordinary magisterium, discussed by Vatican I (1870) and exercised in the dogma on the Immaculate Conception (1854) and the Assumption of the Blessed Virgin Mary (1950).  There have been a number of cases where apparent popes turned out to be false, such as in the case of (probably) Honorius and Liberius, and during the period of the Great Western Schism (1378-1417).