Summa summae S. Thomae, Tomus III

A general council lawfully convoked and confirmed by the supreme Pontiff is infallible in defining questions of faith and morals.

Proof. 1° from all that by which we proved in dissertation III, art. 5, that the universal Church, whether believing or teaching, cannot err; for a general council is the universal Church itself representatively.

Proof. 2° from all that by which we proved the infallibility of the supreme Pontiff; because, if a council confirmed by the supreme Pontiff could err, it would follow that the Pontiff himself would err by confirming erroneous definitions.

Proof. 3°. If a general council confirmed by the supreme Pontiff could err, we should have nothing certain and fixed in the Church, since no greater and more certain judgment than that of such a general council is given.

[Likewise, all the heresies condemned by general councils would revive; for heretics would say that the councils by which they were condemned had erred, or at least had not settled the question. Likewise, we should not know with certainty whether those books are canonical which the councils defined to be canonical: whence faith and religion would be wholly undermined. Likewise, the Church would have been hitherto in intolerable error, proposing as to be believed on faith what had been defined by general councils, which could be false.]

You will object: Aug., lib. II Contra Donat., c. 3, n. 4, says that earlier plenary councils can be corrected by later ones. Therefore he acknowledges them to be fallible.

I answer. I deny the consequence in the sense of the conclusion. For Augustine there speaks of plenary councils, not on questions of faith and morals, on which the conclusion proceeds; but on particular facts, in which we grant that plenary councils can err from false testimonies, and therefore can also be corrected by later councils, namely « when, as the holy Doctor says in the same place, by some experience of events what was closed is laid open, and what lay hidden comes to be known. »

[You will ask whether councils define truths that are new and not yet received in the Church.

I answer. Negatively. A definition issued by a general council is nothing other than the authentic determination of some truth which has always and everywhere been held by the universal Church as certain doctrine, so that by that very fact it stands established that this doctrine belongs to the deposit of divine revelation. It was said above that the universal Church, in which the faithful are to be reckoned as an essential part, is infallible passively, or in believing, so that, if an error in matters of faith and morals should infect some men, and even many, it cannot stain the whole Church or the greater part of the Church, since the Church of the living God is the pillar and firmament of truth, 1 Tim., III, 15. If, therefore, any controversy arises concerning these matters which ought not to be tolerated without detriment to souls, it is authoritatively declared, either by the Pope alone or by the teaching Church, that is, by the bishops judging with the Pope in council, what the universal Church has always held as true regarding the question at issue; and this definition being issued, the doctrine thus solemnly proposed must be held to be believed as of faith.

This is set forth most luminously by Vincent of Lerins in his Commonitorium, lib. I, c. 32 : « What else has the Church ever striven to accomplish by the decrees of her councils, save that what before was believed simply might afterwards be believed more diligently; what before was preached more slackly might afterwards be preached more urgently; what before was practiced more securely might afterwards be practiced more anxiously? This, I say, always, and nothing besides, has the Catholic Church accomplished by the decrees of her councils, aroused by the novelty of heretics, save that what she had before received from her elders by tradition alone she might then consign to posterity also by the written record of Scripture, comprehending a great sum of things in few words, and very often, for the sake of clearness of understanding, not marking out a new meaning of the faith, but signing it with the property of a new appellation.]