So often it happens that historical circumstances force the Church to think through things that have never been thought through before. In our own time, the situation of the St Pius X society has brought to the front just what it might be that constitutes a Council: what solemnity is attached to its teachings, doctrinal and disciplinary, and what degree of submission is required by the faithful in order to describe themselves as Catholic (or indeed O/orthodox)? Must Bishop Fellay and his mates subscribe to every jot and tittle of every document of Vatican II in order to be defined as a Catholic?
My friends will tell you that the matter of what makes or doesn't make a Council infallible has been going round in my mind for some time. Fr Hunwicke has simply encouraged me to write about it, since he is obviously on a not dissimilar tack.
Here, then, are some random thoughts:
1) The word 'council' is a very loose one. There were all sorts of councils in the early Church, regarded as more or less authoritative. In one case in the 4th Century, a semi-Arian council of three hundred or so bishops was held to be overturned by a little council of, I think 24, organized by Athanasius in Alexandria. With hindsight, of course, but I think that this is really the key to status. There is another criterion of solemnity when one comes to Ecumenical Councils. These are councils of the Ecumene, of the world, or at least the parts of the world held to be important (which effectively means the Roman Empire—I never heard of Celtic or Persian Christians participating in an early Ecumenical Council, though I stand to be corrected).
The first 'ecumenical' council is generally agreed to be Nicæa, 325. But what made this any more authoritative than any number of other councils around the same time? Did the participants believe it to be so, just because there were more bishops there than before? The West was not very strongly represented. The actions of some participants subsequently (such as those of Eusebius of Nicomedia) suggest that the answer is no.
One possible answer is that the participation of the Bishop of Rome is the sine qua non for a council that is universally authoritative. And it is certainly true that the Popes or their representatives have taken part in all the councils regarded as 'Ecumenical', though also, presumably, some not so regarded.
There are parts of even ecumenical councils that are now disregarded. Mostly on disciplinary matters, of course, and yet they still have anathemas attached. So what is their status? What, for instance is the status of a bishop who breaches the prohibition of moving from diocese to diocese, this being analogous to adultery? (Nicæa). But then, even a participant of Nicæa, Eusebius of Nicomedia (he had been in another diocese before Nicomedia, too), moved to Constantinople very shortly after the council.
2) Then there is the matter of the preamble and canons. Most councils formulate their material into a discourse followed by canons. The canons at the end are the bits that are considered necessary for a Catholic to believe; they usually conclude anathema sit (condemning those who hold the contrary to the assertion). The preamble is important, but does not require the submission of mind and heart that the canons do.
Vatican II is different. Bd. Pope John XXIII declared that it was to be a 'pastoral council', and therefore that there were to be no anathemas. The consequence is that we have all preamble and no canons. And we find people giving canonical weight, infallible status, to the entire text of Vatican II: something that I suspect we would never have had, had there been canons.
3) The additional problem is actually that those who insist so hard on adherence to the letter of Vatican II are probably far less adhering to its letter than Bishop Fellay. I suspect that Bishop Fellay believes and teaches far more of what is in the documents than do some of his detractors. The things his opponents mean by 'Vatican II' are not really the documents and their contents, but the post-Vatican II 'spirit'.
There is more, illustrated by the Nestorian schism, which will follow when I can get up the energy.
And lest I be accused of heresy or something, if I err, put it down to ignorance. I entirely submit to the judgement of the Church and will rejoice to be corrected.