Chapter XXXV.—Let Heretics Maintain Their Claims by a Definite and Intelligible Evidence. This the Only Method of Solving Their Questions. Catholics Appeal Always to Evidence Traceable to Apostolic Sources.
Challenged and refuted by us, according to these definitions, let all the heresies boldly on their part also advance similar rules to these against our doctrine, whether they be later than the apostles or contemporary with the apostles, provided they be different from them; provided also they were, by either a general or a specific censure, precondemned by them. For since they deny the truth of (our doctrine), they ought to prove that it also is heresy, refutable by the same rule as that by which they are themselves refuted; and at the same time to show us where we must seek the truth, which it is by this time evident has no existence amongst them. Our system 2228 is not behind any in date; on the contrary, it is earlier than all; and this fact will be the evidence of that truth which everywhere occupies the first place. The apostles, again, nowhere condemn it; they rather defend it,—a fact which will show that it comes from themselves. 2229 For that doctrine which they refrain from condemning, when they have condemned every strange opinion, they show to be their own, and on that ground too they defend it.
Indicium proprietatis, a proof of its being their own.