1 When, however, they are confuted from the Scriptures, they turn round and accuse these same Scriptures, as if they were not correct, nor of authority, and [assert] that they are ambiguous, and that the truth cannot be extracted from them by those who are ignorant of tradition. For [they allege] that the truth was not delivered by means of written documents, but vivâ voce: wherefore also Paul declared, “But we speak wisdom among those that are perfect, but not the wisdom of this world.” And this wisdom each one of them alleges to be the fiction of his own inventing, forsooth; so that, according to their idea, the truth properly resides at one time in Valentinus, at another in Marcion, at another in Cerinthus, then afterwards in Basilides, or has even been indifferently in any other opponent, who could speak nothing pertaining to salvation. For every one of these men, being altogether of a perverse disposition, depraving the system of truth, is not ashamed to preach himself.
2. But, again, when we refer them to that tradition which originates from the apostles, [and] which is preserved by means of the succession of presbyters in the Churches, they object to tradition, saying that they themselves are wiser not merely than the presbyters, but even than the apostles, because they have discovered the unadulterated truth. For [they maintain] that the apostles intermingled the things of the law with the words of the Saviour; and that not the apostles alone, but even the Lord Himself, spoke as at one time from the Demiurge, at another from the intermediate place, and yet again from the Pleroma, but that they themselves, indubitably, unsulliedly, and purely, have knowledge of the hidden mystery: this is, indeed, to blaspheme their Creator after a most impudent manner! It comes to this, therefore, that these men do now consent neither to Scripture nor to tradition.
3. Such are the adversaries with whom we have to deal, my very dear friend, endeavouring like slippery serpents to escape at all points. Where-fore they must be opposed at all points, if per-chance, by cutting off their retreat, we may succeed in turning them back to the truth. For, though it is not an easy thing for a soul under the influence of error to repent, yet, on the other hand, it is not altogether impossible to escape from error when the truth is brought alongside it.
Source: Adversus haereses (New Advent)