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Concerning the infamous conflict over the Filioque, it doesn’t appear to be the stumbling block that it once was. In 1995 the Holy Father asked the Pontifical Council for Promoting Christian Unity to reconsider the issue. At his request, they issued a marvelous document entitled: “The Father as the Source of the Whole Trinity - the Procession of the Holy Spirit in Greek and Latin Traditions.”
This document acknowledged the Eastern understanding of the Father as the source of the Trinity as being definitive for the Catholic Church. The Orthodox were concerned that Catholics claimed that the Father and Son BOTH were the source of the Trinity. This document puts that fear to rest.
In fact, this document goes so far as to state that the Creed WITHOUT the Filioque is the normative form of the Creed for the entire Catholic Church. It says:
“The Catholic Church acknowledges the conciliar, ecumenical, normative, and irrevocable value, as expression of the one common faith of the Church and of all Christians, of the Symbol professed in Greek at Constantinople in 381 by the Second Ecumenical Council. No profession of faith peculiar to a particular liturgical tradition can contradict this expression of the faith taught by the undivided Church,” (paragraph no. 2).
The Holy Father has warmly embraced this document, and has implemented it himself. Whenever concelebrating with Eastern bishops, or during ecumenical prayer services, the Holy Father always celebrates the Creed minus the Filioque.
Filioque #2: Why don’t Roman Catholics go back to reciting the Creed in its original form? If a western Church like the Anglican returns to using the Creed without Filioque, then it seems to imply that many Western Christians (Protestant and Roman Catholic) are professing the “wrong” Creed.
To say that the version of the Creed with the Filioque is the “wrong” creed would be incorrect. It is a legitimate variation of the same Creed that is particular to the Latin liturgical tradition.
When properly understood, the Filioque clause does not compromise the monarchy of the Father - the notion that the Father is the original source of the Son and the Spirit. Indeed, the Latin theological tradition has tended to emphasis the role of Son in the spiration of the Spirit while maintaining the Father’s monarchy. The Filioque clause expresses this Latin theological tradition, which is part of the heritage of the Latin Church. Many Roman Catholic theologians believe that to remove the Filioque from the Creed of the Latin Church would be to abandon an important part of the Latin theological patrimony.
Filioque #3: Who started the fight over the filioque? Did Charlemagne really add it to the creed?
Concerning your question, it has been established that the Filioque was inserted into the Nicene Creed at the request of Charlemagne, over the vocal objection of the reigning Pope. It had previously been recited in parts of Gaul and Spain, but it achieved widespread use in the West through the efforts of Charlemagne. Numerous Popes opposed this addition, and attempted to maintain the original version of the creed for several centuries. Indeed, not a single Pope recited the Filioque until Pope Benedict VIII (1014-15).
Thus, when St. Photius protested the recitation of the Filioque in the Creed, he believed himself to be following in the footsteps of the numerous Popes who also opposed this addition.
I should also mention that some historians believe that Charlemagne added the Filioque to the Creed precisely in order to have an excuse for accusing the Byzantine Emperor of heresy. Since the Byzantine Emperor refused to recite the Filioque, he could be accused of heresy and therefore was not to be regarded as a legitimate Emperor by Charlemagne. This meant that Charlemagne alone was the sole true Emperor of the Christian world. Of course, since the Pope at this time also refused to recite the Filioque, this would also mean that he was a heretic by Charlemagne’s standards, wouldn’t it? Thus, Charlemagne painted himself into a sticky theological corner.
In any case, this issue appears to have been largely resolved in recent years. I will be very thankful when this fight is finally consigned to the dustbin of history.
Filioque #4: Do Eastern Catholics have to believe in the filioque?
Rome does not ask Eastern Catholics to abandon our unique theological tradition. In fact, Vatican II has asked us to preserve our theological traditions, which are part of the wealth of the entire Catholic Church. Therefore, Eastern Catholics are to maintain their traditional Eastern theology of the Trinity, which emphasizes the monarchy of the Father.
The filioque is part of the Latin theological tradition. Since we are in full communion with the Roman Catholic Church, Eastern Catholics believe that the filioque is a legitimate understanding of the Trinity, particular to the Latin tradition. In other words, it is a true understanding of the Trinity, equal and complementary with the Eastern understanding. While we do not express our understanding of the Trinity in this way, it is perfectly legitimate for the Latin Church to do so. The Eastern and Western understandings of the Trinity are different but complementary. So when push comes to shove, we believe that the filioque is true, but it is not how we express the mystery.
There is an interesting history behind this. In all of its dealings with the Eastern Orthodox Churches, the Roman Catholic Church has never asked the Orthodox to embrace the filioque as their understanding of the faith. On the contrary, Rome has only asked the Orthodox to acknowledge that it is not heretical. Unfortunately, for many centuries the Orthodox were unwilling to concede this. Some Orthodox Christians still remain so.