But councils of bishops can err and be deceived. How then can one be certain that a particular gathering is truly an Ecumenical Council and therefore that its decrees are infallible? Many councils have considered themselves ecumenical and have claimed to speak in the name of the whole Church, and yet the Church has rejected them as heretical: Ephesus in 449, for example, or the Iconoclast Council of Hieria in 754, or Florence in 1438-9. Yet these councils seem in no way different in outward appearance from the Ecumenical Councils. What, then, is the criterion for determining whether a council is ecumenical?
This is a more difficult question to answer than might at first appear, and though it has been much discussed by Orthodox during the past hundred years, it cannot be said that the solutions suggested are entirely satisfactory. All Orthodox know which are the seven Councils that their Church accepts as ecumenical, but precisely what it is that makes a council ecumenical is not so clear. There are, so it must be admitted, certain points in the Orthodox theology of Councils which remain obscure and which call for further thinking on the part of theologians. With this caution in mind, let us briefly consider the present trend of Orthodox thought on this subject.
To the question how one can know whether a council is ecumenical, Khomiakov and his school gave an answer which at first sight appears clear and straightforward: a council cannot be considered ecumenical unless its decrees are accepted by the whole Church. Florence, Hieria, and the rest, while ecumenical in outward appearance, are not truly so, precisely because they failed to secure this acceptance by the Church at large. (One might object: What about Chalcedon? It was rejected by Syria and Egypt — can we say, then, that it was ‘accepted by the Church at large’?) The bishops, so Khomiakov argued, because they are the teachers of the faith, define and proclaim the truth in council; but these definitions must then be acclaimed by the whole people of God, including the laity, because it is the whole people of God that constitutes the guardian of Tradition. This emphasis on the need for councils to be received by the Church at large has been viewed with suspicion by some Orthodox theologians, both Greek and Russian, who fear that Khomiakov and his followers have endangered the prerogatives of the episcopate and ‘democratized’ the idea of the Church. But in a qualified and carefully guarded form, Khomiakov’s view is now fairly widely accepted in contemporary Orthodox thought.
This act of acceptance, this reception of councils by the Church as a whole, must not be understood in a juridical sense: ‘It does not mean that the decisions of the councils should be confirmed by a general plebiscite and that without such a plebiscite they have no force. There is no such plebiscite. But from historical experience it clearly appears that the voice of a given council has truly been the voice of the Church or that it has not: that is all’ (S. Bulgakov, The Orthodox Church , p. 89).
At a true Ecumenical Council the bishops recognize what the truth is and proclaim it; this proclamation is then verified by the assent of the whole Christian people, an assent which is not, a rule, expressed formally and explicitly, but lived .
It is not merely the numbers or the distribution of its members which determines the ecumenicity of a council: ‘An ‘Ecumenical’ Council is such, not because accredited representatives of all the Autocephalous Churches have taken part in it, but because it has borne witness to the faith of the Ecumenical Church’ (Metropolitan Seraphim, L’Église orthodoxe , p. 51).
The ecumenicity of a council cannot be decided by outward criteria alone: ‘Truth can have no external criterion, for it is manifest of itself and made inwardly plain’ (V. Lossky, The Mystical Theology of the Eastern Church , p. 188). The infallibility of the Church must not be ‘exteriorized,’ nor understood in too ‘material’ a sense: ‘It is not the ‘ecumenicity’ but the truth of the councils which makes their decisions obligatory for us. We touch here upon the fundamental mystery of the Orthodox doctrine of the Church: the Church is the miracle of the presence of God among men, beyond all formal ‘criteria,’ all formal ‘infallibility.’ It is not enough to summon an ‘Ecumenical Council’ … it is also necessary that in the midst of those so assembled there should be present He who said: " I am the Way, the Truth, the Life." Without this presence, however numerous and representative the assembly may be, it will not be in the truth. Protestants and Catholics usually fail to understand this fundamental truth of Orthodoxy: both materialize the presence of God in the Church — the one party in the letter of Scripture, the other in the person of the Pope — though they do not thereby avoid the miracle, but clothe it in a concrete form. For Orthodoxy, the sole ‘criterion of truth’ remains God Himself, living mysteriously in the Church, leading it in the way of the Truth’ (J. Meyendorff, quoted by M. J. le Guillou, Missio et Unité, Paris, 1960, vol. 2, p. 313).
- from The Orthodox Church by Bishop Kallistos Ware
Despite Meyendorff’s assertion that Catholics “materialize the presence of God in the Church”, I think the Catholic take on infallibility is actually very similar to the Orthodox position. The First Vatican Council did not describe ex cathedra statement in terms of “outward criteria alone”, for it starts out "when in the discharge of his office as shepherd and teacher of all Christians … ". (Note that it didn’t say, "the Pope much use such-and-such formula in order for it to be an ex cathedra statement.)
Sorry for the long post.