Question: You mention an Eighth and a Ninth Ecumenical Council, but I thought there were only Seven Ecumenical Councils recognised by Orthodox Christians. What's the story?

 

Answer: It is sometimes stated that Orthodox Christians only recognise seven Ecumenical Councils (Synods). That number arose in Russia under Jesuit influences.  In the Encyclical of the Eastern Patriarchs written in 1848 and signed by bishops of the Holy Synods of Constantinople, Antioch, and Jerusalem, the reader finds repeated references to the Eighth Ecumenical Council.

In an article titled 'The Theological Question of our Day: An Interview with Protopresbyter George Metallinos' published in Divine Ascent: A Journal of Orthodox Faith, Father George stated (all parentheses and brackets in original):

Blessed John Popovich, a confessor of our Faith, has written an important critical treatise on the upcoming Synod. The cause that leads to an Ecumenical Synod is always a specific problem, and the question is, what is the key problem today? If we look at the agenda of the Synod, it seems [as if] we want to formulate a new dogmatic [theology]. Traditionally, the holy Fathers brought three main problems to the council: issues concerning the Trinity, issues concerning Christology, or issues concerning the grace of God and man's salvation. (Of the nine Ecumenical Synods of the Orthodox Church, the Eighth (879-880) and the Ninth (1341) dealt with these problems. The trinitarian problem expresses Orthodox sociology, which is ecclesiology, and the Christological problem expresses Orthodox anthropology.) We do not need anything new today; we only need to live and experience our Orthodox Tradition.
— Vol. 1, Number 2; pp. 59-60

Fr. John Romanides, described by Fr. George Metallinos as 'today's greatest Orthodox theologian of dogmatics', consistently refers to the Eighth and Ninth Ecumenical Councils. See, for example:

The sharp reader may note that the first quote from Father George states that the Ninth Ecumenical Council was in 1341, but the title of the essay by Father John refers to the Ninth Ecumenical Council of 1351.  A typo in one of the sources?  Perhaps.  But there were councils in 1341, 1347, and 1351, held in Constantinople.  They are sometimes referred to as the 'Palamite Councils' because their focus was the dispute between Saint Gregory Palamas and Barlaam of Calabria over hesychasm.  The difference reflects an uncertainty as to which of the Palamite Councils should be deemed 'ecumenical', but at the same time, it demonstrates that the result of the Palamite Councils is accepted by all Orthodox Christians.  Aristeides Papadakis writes:

But if Gregory's insight and solution are important, so is his impact on the later Palamite synthesis. Part of that synthesis was actually prepared in the thirteenth century by Patriarch Gregory II of Cyprus.In a very real sense, the fundamental distinction between the essence and the energy is none other than the "working piece" of Palamas' theology. Even so, its formal ratification as dogma by the Palamite councils of 1341, 1347, and 1351, was foreshadowed in the confirmation of the Tomus at the Council of 1285. Significantly, all Orthodox scholars who have written on Palamas — Lossky, Krivosheine, Papamichael, Meyendorff, Christou — assume his voice to be a legitimate expression of Orthodox tradition. Mutatis mutandis the same is true of Gregory of Cyprus. As one of these scholars has recognized, what is being defined is "one and the same tradition ... at different points, by the Orthodox, from St Photius to Gregory of Cyprus and St Gregory Palamas. Western scholars who have dealt with Gregory II and with Palamas — Jugie, Cayré, Laurent, Candal — have seen fit to attack both of them as revolutionary "innovators." ...
Crisis in Byzantium: The Filioque Controversy in the 
Patriarchate of Gregory II of Cyprus (1283-1289)
, p. 205

 There is far less uncertainty regarding the Eighth Ecumenical Council. The Encyclical of 1848 regards the council held at Constantinople in 879-880 to be the Eighth Ecumenical Council. Thus, it is normal for Orthodox writers to make references to it.  For example Clark Carlton writes:

Remember that it was this Photios who was reconciled to Pope John VIII at the Eighth Ecumenical Council held in 879. At that council the Roman Church condemned the addition of the Filioque to the creed. ...
The Truth: What Every Roman Catholic Should Know
About the Orthodox Church
, page 64, footnote 30

The Eighth Ecumenical Council of 879-880 was affirmed by the patriarchs of Old Rome (Pope John VIII), New Rome [Constantinople] (Saint Photius), Antioch, Jerusalem, and Alexandria and by the Emperor Basil I. This council condemned any 'additions' to the Creed of Nicaea-Constantinople, condemned anyone who denied the legitimacy of the Seventh Ecumenical Council and its decree on icons, and contained an agreement that patriarchates would not interfere in each others' internal affairs. This council was regarded by (Old) Rome (present-day Rome) as the Eighth Ecumenical Council until the eleventh century. At that time, Roman Catholicism found it more convenient to replace it with a council held in Constantinople in 869 (a council that was never accepted in the East and was condemned by the Eighth Ecumenical Council of 879-880). It was at that time that Old Rome began to use the heretical Filioque in the Creed. They could no longer embrace a council which condemned that which they did.

 It should also be remembered that Orthodoxy continued to hold synods which generated canonical sanctions that were then added to the Synodicon. It would take more research to determine when such additions were made, but I know of 843 (the final suppression of iconoclasm), 1077, 1082, and 1117. It is almost certain that there would have been additions in 1341.

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