Before addressing Filioque's Apostolic validity as a matter of theology, we would do well to first explore its canonical validity and the history behind its inclusion in the Western Creed. For, it is often claimed by Eastern Orthodox that the West's insertion of Filioque into the Creed violates Canon VII of the Council of Ephesus (A.D. 431), which reads
"The holy Council decrees that no one should be permitted to offer a different Creed of Faith, or in any case, to write or compose another, than the one defined by the holy fathers who convened in the city of Nicaea… As for those who dare either to compose a different Creed or Faith, or to present one, or to offer one to those who wish to return to recognition of the truth, whether they be Greeks or Jews, or they be members of any heresy whatsoever, they, if bishops or clergymen, shall be deprived as bishops of their episcopate, and as clergymen of their clericate; but if they are laymen, they shall be anathematized.
Likewise, at this same Council, St. Cyril of Alexandria (as Council president) declared:
We prohibit any change whatsoever in the Creed of Faith drawn up by the holy Nicene fathers. We do not allow ourselves or anyone else to change or omit one word or syllable in that Creed.
Now, at first glance, and without resource to historical context, these decrees of the Council of Ephesus seem pretty damning to Filioque.
And, while they are easily addressed and dismissed in the light of authentic history, they do call attention to a much larger difference in the way that modern Catholics and modern Eastern Orthodox view the Church and Church authority, and why it has been so difficult for us to communicate with each other about this particular issue. But, before we delve into this larger (and much more substantive) difference, let's explore why Canon VII of the Council of Ephesus is clearly not a barrier to the inclusion of Filioque.
First of all, please notice how, in the quotes from Canon VII of Ephesus and St. Cyril of Alexandria above, the prohibition is not against adding to the Creed of Constantinople I (A.D. 381), but rather adding to the Creed "defined by the holy fathers who convened in the city of Nicaea" (A.D. 325); and, as we already observed, the Creed of Nicaea makes no mention of the Spirit's procession, but merely reads:
[We believe] in the Holy Sprit… (followed by a direct anathema against Arianism.)
So, if one wishes to be technical about it (as some Eastern Orthodox choose to do by using Canon VII of Ephesus to challenge the legitimacy of Filioque), then one must conclude that Canon VII of Ephesus renders the Constantinopolitan Creed itself illegitimate, since it also "added to" the Creed of Nicaea.
Indeed, an appreciation of the historical context of the Council of Ephesus (A.D. 431), and especially the role of the patriarchate of Alexandria at this Council, is all-important here.
As I already mentioned above, the previous Ecumenical Council (or what would come to be counted as the previous Ecumenical Council), Constantinople I (381), was originally recognized to be a mere regional council of the Eastern Church. Not only did the West not participate in it, but Alexandria, the Church's second see and Eastern primate, was seriously alienated by the proceedings. For, Canon III of the Council of Constantinople unseated Alexandria from its Traditional position as primate in the East (a prerogative implicitly guaranteed by Canon VI of Nicaea) and made Constantinople itself (an episcopate with no Apostolic founder) into the second ranking see after Rome!
So, the Council of Constantinople I (381) – the same Council that drafted the Constantinopolitan Creed (with its reference to the Spirit's procession); and a council that was not yet recognized as ecumenical, but merely regional – was a direct challenge to Alexandria's primal authority in the East. And, as we will soon see, this would dramatically influence the actions of Alexandria at the Council of Ephesus, fifty years later.
Now while, according to Photius (Mansi, III, 596), Rome apparently approved and ratified the dogmatic decrees of Constantinople I (as a mere regional council), Rome did not approve of Canon III and its attempt to give Constantinople primacy over Alexandria and Antioch. Rather, in the very same year, Pope St. Damasus issued the following decree, defending the Traditional integrity of the three Apostolic patriarchates:
Although all the catholic churches spread abroad throughout the world comprise but one Bridal Chamber of Christ, nevertheless, the holy Roman church has been placed at the forefront, not by the councilor decisions of the churches, but has received the primacy by the evangelic voice of our Lord and Savior, Who says: "You are Peter… (Matthew 16:18-19)."
In addition to this, there is also the companionship of the vessel of election, the most blessed Apostle Paul who, along with Peter in the city of Rome in the time of Caesar Nero, equally consecrated the above-mentioned holy Roman church to Christ the Lord; and by their own presence and by their venerable triumph, they set it at the forefront over the others of all the cities of the world. The first see, therefore, is that of Peter the Apostle, that of the Roman church, which has neither stain nor blemish, nor anything like that. The second see is that of Alexandria, consecrated on behalf of the blessed Peter by Mark, his disciple and an Evangelist, who was sent to Egypt by the Apostle Peter, where he preached the word of truth and finished his glorious martyrdom. The third see is that of Antioch, which belonged to the most blessed Peter, where first he dwelled before he came to Rome, and where the name 'Christians' was first applied, as to a new people. (Decree of Damasus #3, 382 A.D.)
This was written in defense of Alexandria and as a direct refutation of Canon III of the Council of Constantinople I, which, remember, was only seen as a regional council at the time. And, sixty-nine years later, Pope St. Leo the Great (Ep. cvi in P.L., LIV, 1003, 1005) would repeat this condemnation and declare that Canon III of Constantinople I was never accepted by Rome and (like Canon XXVIII of Chalcedon) was a violation of the Nicene order (i.e., Canon VI of Nicaea).
Indeed, this move by the Council of Constantinople I (to make the imperial capital the Eastern primate in place of Alexandria) would also inspire a bitter and ongoing "feud" between Alexandria and Constantinople, in which Alexandria became very zealous (indeed, almost paranoid) about defending its Apostolic prerogatives, and so its primacy in the East over Constantinople. This agenda was clearly at play when, two decades after Canon III was drafted, Patriarch Theophilus of Alexandria, the immediate successor of Patriarch St. Timothy of Alexandria (who had attended Constantinople I), condemned St. John Chrysostom (then, Bishop of Constantinople, A.D. 398-404) and stripped him of his see. It was also clearly at play when Theophilus' nephew and immediate successor, St. Cyril of Alexandria, condemned the heretical Nestorius (Bishop of Constantinople from A.D. 428-431) and presided over the Ecumenical Council of Ephesus against him.
