The First Vatican Council infallibly taught the following.
“For the holy Spirit was promised to the successors of Peter not so that they might, by his revelation, make known some new doctrine, but that, by his assistance, they might religiously guard and faithfully expound the revelation or deposit of faith transmitted by the apostles. Indeed, their apostolic teaching was embraced by all the venerable fathers and reverenced and followed by all the holy orthodox doctors, for they knew very well that this see of St. Peter always remains unblemished by any error, in accordance with the divine promise of our Lord and Savior to the prince of his disciples: ‘I have prayed for you that your faith may not fail; and when you have turned again, strengthen your brethren.’
“This gift of truth and never-failing faith was therefore divinely conferred on Peter and his successors in this See so that they might discharge their exalted office for the salvation of all, and so that the whole flock of Christ might be kept away by them from the poisonous food of error and be nourished with the sustenance of heavenly doctrine. Thus the tendency to schism is removed and the whole church is preserved in unity, and, resting on its foundation, can stand firm against the gates of hell.” [Vatican I, First Dogmatic Constitution on the Church, chapter 4, n. 6-7.]
The Council interprets Sacred Scripture as teaching that the faith of Peter “and his successors in this See” is never-failing. This teaching is in a Dogmatic Constitution. It is also said to be the consistent teaching of the Church from the time of the early Church fathers, a teaching held by all the holy orthodox doctors after them. Therefore, this is an infallible teaching, which is divinely-revealed.
Therefore, the faithful must believe, as a formal dogma, the denial of which is the grave sin of heresy, that every valid Pope, including Pope Francis and all his predecessors and successors, is prevented by the grace of God from ever committing the grave sins which are failures of faith: apostasy, heresy, and schism.
What, then, does the gift of truth add to this gift of a never-failing faith? The gift of truth, by the grace of God, prevents each Pope from ever teaching heresy of any kind. Not only can he not commit the deliberate sin of formal heresy, but he also cannot inadvertently teach material heresy, nor be guilty of propagating heresy, nor teach any grave error on faith, morals, and salvation, nor any error that would lead the faithful away from the path of salvation. For “this see of St. Peter always remains unblemished by any error.” And there are other teachings of the Magisterium, similarly (throughout Denzinger).
But now we have a slight theological problem. Vatican I also taught that the teachings of each Pope are only infallible (free from all error) when certain conditions are met. And we know from the teachings of Popes John XXIII, John Paul II, and Benedict XVI that the Popes themselves admit that much of their teaching is “non-infallible” and “non-irreformable”. So how can the See of Peter be “unblemished by any error”, when only certain teachings are entirely free from error?
I would say that the answer is found in various well-accepted acts of contrition, used in the Sacrament of Reconciliation. In these prayers, the penitent states that, with the help of God’s grace, he will not sin again. And yet we all know that poor fallen sinners cannot avoid every venial sin, except for those few persons who have been given a special grace from God [Trent, Justification, Canon 23]. The meaning is that he will strive not to sin gravely; and he may well succeed in this resolve, since we are each and all able to avoid every actual mortal sin. And he further implies by this prayer the resolve to try to avoid venial sin. However, the penitent is not literally promising never to sin at all ever again. For he knows his own weakness in the fallen state.
Similarly, the See of Peter is unblemished by any grave error, but the limited errors that may occur in non-infallible teachings are simply not included in this assertion. The Holy Spirit not only protects the infallible teachings of the Pope from every error, He also protects the non-infallible teachings of the Pope from grave error. But it cannot be the case that God protects every teaching of the Pope from every error, or the dogma of the First Vatican Council on Papal Infallibility would be null and void.
A Common Objection
One common claim on this topic is that a valid Pope can teach heresy, and by doing so he becomes not the Pope and not a member of the Church any longer. And so, it is claimed, the Pope has not erred — for his errors made him no longer the Pope. Something similar is said of the Magisterium. It is claimed that the Magisterium cannot err at all, but if a Pope or Bishop or Ecumenical Council (!!!) do assert an error, that error is automatically not of the Magisterium. This claim is absurd.
It is like giving someone a gift, along with the claim: “The gift I gave you is unbreakable.” And when the gift is dropped, and it shatters, the gift-giver says: “Now that it is shattered, it is no longer my gift, and so my promise that the gift would be unbreakable remains true.” It makes no sense to say that the Magisterium cannot err because, if it errs, all such errors are not of the Magisterium. This leaves the faithful to their own devices to determine which teachings to accept and which to classify as “not of the Magisterium”. And the same is true for the Pope. If each Pope who teaches heresy become “not the Pope anymore”, we would each have to judge every teaching of every Pope. Then, not knowing which Popes are valid, we would not know which Councils are valid, and all the teachings of the Church would be placed in doubt.
Instead, the truth is this: The Church founded by Jesus Christ has His promise that She will never be broken by teaching grave error, nor by leading the faithful astray in either discipline or doctrine. And since the Pope is the head of the Church and is indispensable to every mode of infallibility of the Magisterium, the Pope too is indefectible. He can’t teach grave error, not even as a mere personal opinion. He can’t commit apostasy, heresy, or schism. And he can’t become an invalid Pope by teaching or adhering to grave error. But this also implies that the body of Bishops, as a body not as individuals, is indefectible in much the same way. For Christ did not choose one Apostle, Peter, but Twelve Apostles (Matthias replacing Judas), with Peter as their head.
More in my book: In Defense of Pope Francis
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