Jesus promises that the gates of hell would not prevail against his Church, and that the Holy Spirit would lead her into all truth. Traditionally, the Catholic and Orthodox churches have taken that to entail that the Church as a whole is indefectible. Not only will one, catholic, and apostolic Church perdure to the end of history; that Church is and always will be holy, as the Bride of Christ whom he has made holy. One consequence of that in turn is the infallibility of the Church's teaching office, what the Catholic Church calls "the Magisterium." Whatever local or peripheral errors may and do arise, God will never permit the Church to teach with her full authority something that is incompatible with the faith "once delivered to the saints" (Jude 3). Teachings propounded with her full authority are identified in certain ways. The standard way is by dogmatic definition, either by councils ratified by the pope as binding on the whole Church, or by popes unilaterally. Thus for any doctrine P, if a council and/or pope says that "If anyone denies that P, let him be anathema," then P is a dogma taught with the full authority of the Church, and as such is set forth infallibly. That is the exercise of the "extraordinary magisterium," which affords Catholics a proximate object for the assent of faith, and thus for the virtue of faith; that entails a kind of certainty as great as, albeit of a different kind from, the sort of certainty we can have about, say, truths of arithmetic. Indeed, a formal list of doctrines so propounded could be produced, and for all I know has been produced. But there has never been much interest in such a thing, for the simple reason that it wouldn't address any particular question that remains controversial in the Church. The real controversy is about whether certain doctrines not so defined have nonetheless been set forth infallibly. In other words, the vexed question among Catholic theologians is about the extent of the ordinary and universal magisterium's infallibility ('IOUM' for short).
For reasons I've explained before, (see the sidebar, "Articles of Mine"), there clearly is such a thing as IOUM. The issue is an interesting study in the development of doctrine, for those who are interested in that sort of thing. But the objection is sometimes raised in certain quarters that assent to teachings set forth infallibly by the OUM cannot be certain, because one cannot identify with certainty just which teachings have been thus set forth. Although a few such teachings have been so identified, there neither is nor could be a list of such teachings that is both exhaustive and authoritative. There are a number of reasons for that, one of which is that such a list would function de facto as an exercise of the extraordinary magisterium, which would effectively render the OUM nugatory, which neither is nor could ever practically be the case. And that raises what some claim is a problem for the Catholic. Thus:
First, one must determine what documents and decrees could be considered infallible. Second, one must determine exactly what is or is not infallible within those documents/decrees. Is the determination of the above made fallibly or infallibly? And by whom is such a determination made?
Now as I've implied before, there can be no question for the faithful Catholic that whatever is defined as dogma by the extraordinary magisterium is to be "considered infallible" (assuming we allow the word 'infallible' to apply to statements, not just persons or collections thereof, by analogy of attribution). For that class of cases, there are clear answers in principle to above-quoted questions, and that is enough for faithful Catholics, most of whom possess no list of such teachings and feel no need to. Of course that won't be enough for somebody who is not a faithful Catholic; but the Church does not teach that whatever is said to be infallibly defined is going to be persuasive on that account to people who aren't faithful Catholics, nor should we expect it to be.
Yet even aside from the question of IOUM in particular, there is an objection to the very idea of infallibility itself. In the combox to the post I've quoted above, a reader writes:
1) I'd like to know how, since you are a fallible individual, you know infallibly that... all the decrees and definitions contained in the Ecumenical Councils concerning faith and morals...are infallible.
2) because Vatican I states that they are.
We both agree, however, that Scr[ipture] is infallible. We don't agree that RCC dogma is infallible, so your objection doesn't work.
Maybe this would be a better example of what I mean: Vatican I depends on a previous statement of the Church that it can produce infallible proclamations. 2 questions:
1) what is that proclamation?
2) How do you know the proclamation that the RCC can make infallible statements is itself an infallible statement?
It should, but apparently does not, go without saying that some of the same questions can be raised, and answered, about that infallibility of Scripture itself which is affirmed by the author. But the very first question raised by that person is silly in the sort of way that the paradox of humility is silly. Leave aside the fact that no human person, not even the pope, is infallible as a matter of personal virtue; one can never establish the infallibility of one's assent to anything, because one can always raised the question about the infallibility of the establishment, and so on ad infinitum. Moreover, such a pseudo-question has nothing to do with the infallibility with which such truths are proposed by the Church. And even the infallibility of the Church is no evidence whatever, to somebody who does not antecedently accept the authority of the Church, of the truth of what's thereby proposed. So the very last question, which invites another silly infinite regress, is not worth getting tied up in knots over either. Just as one cannot be maintain the virtue of humility by reflecting on one's humility, so one cannot maintain the virtue of faith by reflecting on the degree of certainty one's faith enjoys. For the Catholic it suffices, and ought to suffice, simply to trust that the Church is preserved by God from error about the deposit of faith when she teaches thereon with her full authority. One doesn't have to know, in each and every instance, when the Church has done that; all that's needed is to know that there have been clear instances when, according to universally acknowledged criteria, she has done so.
The problem here is one that I can't think of a better way to describe than as a kind of obsessiveness. There are some people who fear that the only alternative to having every single "i" dotted and "t" crossed is every man for himself, at least in matters of faith. This is not the way to come at the problem of authority in forming the virtue of faith. The way to come at it is not to fret about what is sufficient for dispelling every difficulty and doubt, but to ask what is necessary for the transmission of the deposit of faith as an object of faith, as distinct from human opinion.