The Commonitorium

[7.] What then will a Catholic Christian do, if a small portion of the Church have cut itself off from the communion of the universal faith? What, surely, but prefer the soundness of the whole body to the unsoundness of a pestilent and corrupt member? What, if some novel contagion seek to infect not merely an insignificant portion of the Church, but the whole? Then it will be his care to cleave to antiquity, which at this day cannot possibly be seduced by any fraud of novelty.

[8.] But what, if in antiquity itself there be found error on the part of two or three men, or at any rate of a city or even of a province? Then it will be his care by all means, to prefer the decrees, if such there be, of an ancient General Council to the rashness and ignorance of a few. But what, if some error should spring up on which no such decree is found to bear? Then he must collate and consult and interrogate the opinions of the ancients, of those, namely, who, though living in divers times and places, yet continuing in the communion and faith of the one Catholic Church, stand forth acknowledged and approved authorities: and whatsoever he shall ascertain to have been held, written, taught, not by one or two of these only, but by all, equally, with one consent, openly, frequently, persistently, that he must understand that he himself also is to believe without any doubt or hesitation.