Why is there only 7 ecumenical councils according to the Orthodox? What about references to an 8th or even 9th ecumenical council?
The first Seven Ecumenical Councils are recognized as authentic and trustworthy witnesse to the Truth of the Gospel by both the Eastern Orthodox and Roman Catholic Churches. They took place in the unique framework of the Roman Empire and were approved by the five ancient Patriarchates (including Rome). They are considered Ecumenical in the sense that the teachings of these councils was subsequently received by all the Orthodox Catholic Churches.
However, it is true that the Encyclical of the Eastern Patriarchs written in 1848 and signed by bishops of the Synods of Constantinople, Antioch, and Jerusalem, makes repeated references to the Eighth Ecumenical Council.
This is a reference to the Council of 879-880 which was approved by the patriarchs of Rome (Pope John VIII), Constantinople – New Rome (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 while acknowledging the primacy of Rome and Rome’s right to hear appeals.
On the basis of the Encyclical of 1848, it would certainly be acceptable for an Orthodox Christian to adopt the view that the Council of 879-880 could or should be considered as Ecumenical (noting that this council is absolutely rejected by the Roman Catholic Church, unlike the first 7).
There seems to be much less of a basis for the view that the councils held in 1341, 1347, and 1351 in Constantinople (sometimes referred to as the ‘Palamite Councils’) have ever widely been considered as Ecumenical in the same sense.