During the prelude to the First Vatican Council, the idea of a heretical pope was
used as the primary argument against the solemn definition of papal infallibility.
The medieval canonists and conciliarists had allowed for the notion of papal heresy
by making a strict distinction between the apostolic seat itself and the individual
occupants of the throne of Peter. However, when we examine the text of Pastor
Aeternus in light of the contents of the official Relatio, which was drawn up at the
council to explain the meaning of this document, we find that the above distinction
used by the conciliarists was formally proscribed with an anathema. This article will
argue that in doing so, the Council Fathers definitively excluded the possibility of a
heretical pope.