Since it seems that DHK has arrived at a distorted opinion of both Vincent himself and his "canon" from what he has read in the Wikipedia article, I thought I'd chime in with words "straight from the horses mouth" along with some comments...
From Vincent's Commonitory:
"I have often then inquired earnestly and attentively of very many men eminent for sanctity and learning, how and by what sure and so to speak universal rule I may be able to distinguish the truth of Catholic faith from the falsehood of heretical pravity; and I have always, and in almost every instance, received an answer to this effect: That whether I or any one else should wish to detect the frauds and avoid the snares of heretics as they rise, and to continue sound and complete in the Catholic faith, we must, the Lord helping, fortify our own belief in two ways; first, by the authority of the Divine Law, and then, by the Tradition of the Catholic Church."
So here Vincent states the ways distinguish truth from error is to appeal to both Scripture ("the Divine Law") and Tradition. This two-fold appeal is not new with him and is amply demonstrated in the writings of earlier church fathers both ante-Nicene and post-Nicene.
"But here some one perhaps will ask, Since the canon of Scripture is complete, and sufficient of itself for everything, and more than sufficient, what need is there to join with it the authority of the Church's interpretation? For this reason,—because, owing to the depth of Holy Scripture, all do not accept it in one and the same sense, but one understands its words in one way, another in another; so that it seems to be capable of as many interpretations as there are interpreters. For Novatian expounds it one way, Sabellius another, Donatus another, Arius, Eunomius, Macedonius, another, Photinus, Apollinaris, Priscillian, another, Iovinian, Pelagius, Celestius, another, lastly, Nestorius another. Therefore, it is very necessary, on account of so great intricacies of such various error, that the rule for the right understanding of the prophets and apostles should be framed in accordance with the standard of Ecclesiastical and Catholic interpretation."
So after stating his belief in the (material) sufficiency of Scripture, Vincent argues that the Church's standard interpretive Tradition is necessary because of the various ways in which different people (particularly heretics) have misinterpreted the Scriptures. To make this especially relevent to the situation today, and why the consensus of Tradition is necessary, one can substitute modern-day denominations and see how his argument still holds:
"For this reason,—because, owing to the depth of Holy Scripture, all do not accept it in one and the same sense, but one understands its words in one way, another in another; so that it seems to be capable of as many interpretations as there are interpreters. For Luther expounds it one way, Calvin another, Zwingli another, Methodists, Baptists, Mennonites, another, Adventists, Pentecostals, Presbyterians, Unitarians, Quakers, Campbellites, Plymouth Brethren, another, lastly, Jehovah Witnesses another. Therefore, it is very necessary, on account of so great intricacies of such various error, that the rule for the right understanding of the prophets and apostles should be framed in accordance with the standard of Ecclesiastical and Catholic interpretation."
Now regarding the idea of "universality, antiquity, and consent" that Matt and I have been discussing, it's clear that DHK has misundertood this. Here is Vincent in his own words:
"Moreover, in the Catholic Church itself, all possible care must be taken, that we hold that faith which has been believed everywhere, always, by all. For that is truly and in the strictest sense "Catholic," which, as the name itself and the reason of the thing declare, comprehends all universally. This rule we shall observe if we follow universality, antiquity, consent. We shall follow universality if we confess that one faith to be true, which the whole Church throughout the world confesses; antiquity, if we in no wise depart from those interpretations which it is manifest were notoriously held by our holy ancestors and fathers; consent, in like manner, if in antiquity itself we adhere to the consentient definitions and determinations of all, or at the least of almost all priests and doctors."
So as you see, his methodology has nothing to do with some syncretism or vague ecumenism or secularism, but rather has to do with the common belief within the Church across space and time back to the Apostles.
Next Vincent offers principles for applying these criteria:
"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.
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."
(This should be pretty self-explanatory)
As for the man himself, even the Wikipedia article acknowledges that although he was suspected of what has been called "semi-Pelagianism", he was never condemned as a heretic. One must recall (from the article) that he is commemorated as a "saint" in the RCC (I don't think they commemorate formal heretics). One must also keep in mind that "semi-Pelagianism" is a vague category applied to men who basically had in common an opposition to the more extreme expressions of Augustinianism. (Although what has been later called "semi-Pelagianism" was condemned at the Council of Orange, it is unclear whether some of these men, who lived before then, actually held to what was condemned.