p. xv III. The Number of the Ecumenical Synods.
It may not be unjustly expected that some reasons should be assigned for limiting the number of the Ecumenical Synods to seven. There is no need here to enter into any proof that Nice, I. Constantinople, Ephesus and Chalcedon are Ecumenical, since so long ago as the time of St. Gregory the Great, that Saint and Doctor said of them: “I venerate the first four Ecumenical Councils equally with the Four Gospels (sicut quatuor Evangelia),” 10 and no one has been found to question that in so saying he gave expression to the mind of the Church of his day. Of the fifth and sixth synods there never was any real doubt, although there was trouble at first about the reception of the fifth in some places. The ecumenical character of the seventh is not disputed by East or West and has not been for near a thousand years, and full proof of its ecumenicity will be found in connection with that council. There is therefore no possible doubt that these seven must be included, but it may be asked why certain others are not here also.
The reasons for rejecting the claims of Sardica will be found in connection with the canons set forth by that council. The same is the case with regard to the claims of the Synod in Trullo. It is true that IV. Constantinople, holden in a.d. 869, was for a short while held as Ecumenical by both East and West, and continues to be held as such by the Latin Church down to this day, but it was soon rejected by the East and another synod of Constantinople (879), which undid much of its work, has for the Greeks taken its place. However the Easterns do not claim for this synod an ecumenical character, but confine the number to seven.
The Councils of Lyons and Florence both fail of ecumenicity for the same reason. At both the East was represented, and at each an agreement was arrived at, but neither agreement was subsequently accepted in the East, and the decrees therefore have failed, as yet, of receiving ecumenical acceptance.