In my youthful naïveté, I long ago took (a) for granted, i.e., that there is such a thing as the infallibility of the OUM. For reasons that will become clear in this post, I still believe I was justified in doing so. But I have found over the decades that (a) is not taken for granted in the Church at large. Most rank-and-file Catholics are unaware of (a), even as a thesis, and the majority of Catholic ecclesiologists either disbelieve (a) or have not explored the issue in depth. (The main exception is the indefatigable Jesuit Francis Sullivan, whose scholarly writings have indeed addressed the issue in depth, but have not managed, at least to my mind, to clarify it much. And of course a minority of faithful theologians, such as Germain Grisez and William May, do hold (a).) In the form raised at and since Vatican II, the issue itself rarely even came up explicitly before the 20th century. Since the Counter-Reformation, of course, there's always been discussion among theologians about whether this-or-that non-dogmatic teaching is irreformable; but until the 1990s, there had been little clarity either from the Magisterium or from theologians about the general criteria for identifying non-dogmatic teachings precisely as IOUM. The issue seemed to have been left as almost entirely a matter of opinion, if not of intuition. Ironically, though, the reason for that is also one of the reasons why Catholics, whether ordinary lay people or professional theologians, can and ought to take (a) for granted. That reason takes its place as part of the larger argument I aim to develop.
Even relatively "progressive" Catholics take for granted that the Church as a whole is "indefectible" in the truth. That means that, in the Church, the deposit of faith given "once-for-all to the holy ones" (cf. Jude 3) will always be preserved and taught faithfully. That belief belongs to sacred Tradition, and thus itself to the deposit of faith. Of course it does not tell us, by itself, which individuals in the Church will remain faithful to the entire deposit of faith. But by the same Tradition, Catholics profess that there is a body in the Church, namely the episcopal college with the pope as its head, who by divine authority teach to the Church as a whole; that is what is meant by the term 'Magisterium', the "teaching authority" of the Church.
Now when those who exercise the Magisterium teach authoritatively to the Church as a whole about a matter comprised by the deposit of faith, they also speak authoritatively for the Church as a whole. As the Mystical Body of Christ, the Church is the "sacrament" of salvation in and for the world; it is thus in and through her that what God has revealed in and through Christ is given to the world. Hence, whoever speaks authoritatively for the Church thereby preaches the Gospel authoritatively not only to the Church but to all humanity. But there just isn't anybody besides the bishops, in union with the pope, who have divinely given authority to speak for the Church as a whole—even when, at a particular time and on a particular issue, the majority of bishops happen to be heterodox and the majority of non-bishops orthodox, as has occasionally occurred in the Church's history. (The question how such anomalies are to be resolved raises rather quickly a major issue between Catholicism and Orthodoxy; but that is another issue for another time.) Now since the Church as a whole is indefectible in that truth which is contained in the deposit of faith, she cannot speak error about said deposit when she speaks as a whole. Therefore, when the Magisterium teaches authoritatively as a body to the Church as a whole about a matter comprised by the deposit of faith, it is preserved by God from teaching error about that matter. In other words, it teaches infallibly. And what is taught infallibly is ipso facto irreformable.
That is why Vatican I, in defining specifically papal infallibility, said that when the pope defines a doctrine on "faith or morals" infallibly, he does so only with "that infallibility which the Church enjoys" in such matters. Papal infallibility is not a personal quality of any man; it is but a specification of the infallibility of the Church as a whole. But papal infallibility is not the only or even the most important way in which the Church manifests her infallibility about matters of faith and morals.
As most of my readers know, there are two general ways for either the episcopal college as a whole or the pope in particular to exercise the Magisterium: the "ordinary" and the "extraordinary." As I wrote in an article I published a few years ago (adding emphasis now):
The ordinary magisterium is simply the teaching authority of the Church as exercised in ordinary, day-to-day circumstances. The extraordinary magisterium is the teaching authority of the Church as exercised in special circumstances calling either for resolution of a disputed question or clarification of traditional doctrine in more precise and authoritative terms; almost always, that occurs by means of the decrees of a general council or an explicit papal definition [ex cathedra]. The ordinary magisterium proposes for our belief the entire deposit of faith entrusted to the Church by Jesus Christ him self for preservation and ever-deeper but never-exhaustive understanding; the extraordinary does not add to that deposit, but expresses this or that aspect of it in terms that may never be repudiated even if and when they can be improved. Traditionally, and not terribly controversially, Catholic theologians acknowledge the exercise of the extraordinary magisterium as manifesting the infallibility of the Church as a whole. And in theory at least, most will now grant that the ordinary magisterium can also be exercised infallibly by the bishops as a whole, with or without formal papal confirmation. Thus Lumen Gentium §25:
Although the individual bishops do not enjoy the prerogative of infallibility, they nevertheless proclaim Christ’s doctrine infallibly whenever, even though dispersed through the world, but still maintaining the bond of communion among themselves and with the successor of Peter, and authentically teaching matters of faith and morals, they are in agreement on one position as definitively to be held [definitive tendendam]. This is even more clearly verified when, gathered together in an ecumenical council, they are teachers and judges of faith and morals for the universal Church, whose definitions must be adhered to with the submission of faith.
The standard way in which the infallibility of the extraordinary magisterium is exercised is by means of "definitions" issued by the bishops "gathered together in an ecumenical council." Many dogmas have been defined in that fashion; precisely as such, they are irreformable and require the unqualified assent of the faithful. So much is also Tradition, and as such has remained relatively uncontroversial in the Church. Dogmas so defined are vastly greater in number than those unilaterally and infallibly defined by popes, which are few and relatively recent. But it is at this point that our main question arises: granted how the episcopal college manifests its infallibility as a whole by means of its extraordinary magisterium, can it manifest its infallibility as a whole by exercising only its ordinary magisterium?
For two reasons, the answer to that question has to be affirmative.
First, the very authority of the extraordinary magisterium depends on it. When said magisterium, either of the episcopal college as a whole or of the pope individually as its head, defines a doctrine as dogma, it does not materially add anything to the deposit of faith. It merely makes clearer or otherwise more explicit some aspect of that truth which was always comprised by said deposit and believed as such by the Church. And it is the entire deposit that the Church indefectibly professes and teaches over time; nothing is lost even when some forget it. But prior to formal definition, no aspect of the deposit is taught by the extraordinary magisterium; for formal definition is the exclusive province of the extraordinary magisterium. Indeed, before there was any exercise of the extraordinary magisterium by and for the Church as a whole—i.e., before the fourth century—the deposit was indefectibly preserved and taught, whole and entire, by the OUM. Therefore, the OUM did so infallibly; for if it had not, there would have been no subject matter for the extraordinary magisterium to present as the sure and certain truth that God reveals and the Church believes; there would only have been, at best, pious opinions and traditions. This is also why the extraordinary magisterium has never even seen fit to define its own authority. Such a definition would be viciously self-reflexive if the infallibility of dogmatic definition by the extraordinary magisterium were not always, itself, been an IOUM doctrine and understood as such. But given that it has always been IOUM and understood as such, there is no need for the same belief to be formally defined by the extraordinary magisterium.
The second reason why there must be such a thing as the infallibility of the OUM is that, if the Church as a whole is indefectible in professing what's comprised by the deposit of faith, then whoever is divinely authorized to speak for the Church as a whole in professing that which is "to be held definitively" as belonging to said deposit—in this case, the episcopal college—speaks infallibly when they teach to the Church as a whole what is thus professed. But there is no traditional belief to the effect that the bishops can do that only when physically together or are otherwise in a position to issue an act of definition. It is quite possible for the bishops to be "in agreement on one position as definitively to be held" while being spread out over the world or even over history. Such agreement or consensus can thus be either synchronic (i.e., at a particular time) or diachronic (i.e., over time). One example of a "position to be definitively held" in such fashion is that God loves all people—a doctrine which has never been formally defined as dogma, and which some heretics have denied, but which the bishops and the pope have long taught with diachronic consensus. That doctrine is therefore IOUM. There is of course no guarantee that IOUM doctrines were never controversial or will always remain uncontroversial. Although, for example, Christians have always professed that God created the universe, the Bible did not make clear that God's act of creation is ex nihilo—i.e., done without any pre-existing material to work on. But once philosophical and theological reasoning reached that conclusion, it was universally accepted and became IOUM.
Now even granted that there is such a thing as IOUM, the question remains whether it is itself a matter of doctrine, or only a matter of opinion, whether a given doctrine is in fact IOUM and is thus "irreformable." That question becomes very important when the doctrines at issue are old but have never been defined formally, and have also become controversial in the Church. The best-known examples of such doctrines today are the Church's lack of authority to ordain women and the intrinsic wrongfulness of contraception. In my next post, I shall argue that although the Church sometimes and wisely leaves it to theologians to debate the question whether a given doctrine is IOUM, the Magisterium must have the authority to rule in such a way as to settle the question definitively, and has in fact begun to do so.