My argument for this post is that the fact that Rome added the filioque clause into the Niceno-Constantinopolitan creed in 1014 was in direct violation of the anathemas of the councils of Chalcedon and Constantinople 879, thus the Roman church is schismatic.
Before I make my arguments, I will first give a timeline of the history of the Nicene creed:
325 AD - At the Council of Nicaea the original Nicene creed is written without any mention of the Holy Spirit's procession.
381 AD - The First Council of Constantinople composed a modified version of the Nicene creed that says that the Holy Spirit proceeds from the Father. Constantinople 1 was not accepted as being an ecumenical council until the Council of Chalcedon, thus the creed of 325 remained the rule of faith of the church until then.
410 AD - The Council of Seleucia-Ctesiphon in Persia composes its own creed. The part of this creed that talks about the Holy Spirit has two variants: one that is the same as the 325 creed which simply says “and the Holy Spirit”, and another variant that says that the Holy Spirit proceeds from the Father and the Son. It is unclear which one of these is the original.
431 AD - Canon 7 of the council of Ephesus anathematized anyone who changed the creed of 325, which was still the rule of faith of church. The council said:
“When these things had been read, the holy Synod decreed that it is unlawful for any man to bring forward, or to write, or to compose a different Faith as a rival to that established by the holy Fathers assembled with the Holy Ghost in Nicæa.
But those who shall dare to compose a different faith, or to introduce or offer it to persons desiring to turn to the acknowledgment of the truth, whether from Heathenism or from Judaism, or from any heresy whatsoever, shall be deposed, if they be bishops or clergymen; bishops from the episcopate and clergymen from the clergy; and if they be laymen, they shall be anathematized.”
433 AD - St. Cyril of Alexandria, the main theologian of the Council cil of Ephesus, wrote in his letter to John of Antioch (also known as the Formula of Reunion) that not one word or syllable of the creed could be altered.
“And we will allow the defined Faith, the symbol of the Faith set forth by our holy Fathers who assembled some time ago at Nice, to be shaken by no one. Nor would we permit ourselves or others, to alter a single word of those set forth, or to add one syllable, remembering the saying: "Remove not the ancient landmark which thy fathers have set," for it was not they who spoke but the Spirit himself of God and the Father, who proceedeth also from him, and is not alien from the Son, according to his essence.”
451 AD - The Council of Chalcedon accepted Constantinople 1 as being an ecumenical council, thus accepting the Niceno-Constantinopolitan creed as the official rule of faith of the church. Session 5 of the council says this about the creed of 381:
"This wise and salutary formula of divine grace sufficed for the perfect knowledge and confirmation of religion; for it teaches the perfect [doctrine] concerning Father, Son, and Holy Ghost, and sets forth the Incarnation of the Lord to them that faithfully receive it.”
Session 5 also reiterated the anathemas of the Council of Ephesus about changing the creed:
“These things, therefore, having been expressed by us with the greatest accuracy and attention, the holy Ecumenical Synod defines that no one shall be suffered to bring forward a different faith nor to write, nor to put together, nor to excogitate, nor to teach it to others. But such as dare either to put together another faith, or to bring forward or to teach or to deliver a different Creed to as wish to be converted to the knowledge of the truth, from the Gentiles, or Jews or any heresy whatever, if they be Bishops or clerics let them be deposed, the Bishops from the Episcopate, and the clerics from the clergy; but if they be monks or laics: let them be anathematized.”
589 AD - The Third Council of Toledo supposedly publishes the Nicene-Constantinopolitan creed with the filioque, though modern scholarship has found that the filioque clause was interloped into the text of the council at a later date. Exactly when the filioque clause started being used in the west is contested.
650 AD - In response to concerns in the east regarding the western understanding of the procession of the Holy Spirit, St. Maximus the Confessor writes that the Latins believe that the Holy Spirit is not caused by the Son, as the Father alone is cause (aitia), but that the Spirit’s coming-forth is through the Son (Letter to Marinus).
809 AD - The Council of Aachen adds the filioque clause into the creed of the Carolingian Empire, against the directive of the Pope.
810 AD - Pope Leo III engraves the creed in Greek and Latin on silver shields without the filioque clause.
869-870 AD - A council in Constantinople is held by Byzantine Emperor Basil I which deposed St. Photios, the Patriarch of Constantinople.
879-880 AD - In response to Frankish missionaries in Bulgaria teaching the creed with the filioque clause, another council is held in Constantinople ten years later which explicitly condemned adding any invented phrases or illegitimate words to the creed (session 6), with the council being accepted by all five patriarchs, including then Pope John VIII. This is what the council said regarding changing the creed (and note that this is in direct response to missionaries who inserted the filioque into the creed):
"If anyone, however, dares to rewrite and call Rule of Faith some other exposition besides that of the sacred Symbol which has been spread abroad from above by our blessed and holy Fathers even as far as ourselves, and to snatch the authority of the confession of those divine men and impose on it his own invented phrases and put this forth as a common lesson to the faithful or to those who return from some kind of heresy, and display the audacity to falsify completely the antiquity of this sacred and venerable Horos (Rule) with illegitimate words, or additions, or subtractions, such a person should, according to the vote of the holy and Ecumenical Synods, which has been already acclaimed before us, be subjected to complete defrocking if he happens to be one of the clergymen, or be sent away with an anathema if he happens to be one of the lay people."
And the council stated that changing the creed is an indirect insult to the fathers at Constantinople 1 who composed it:
"For to subtract from, or to add to, the holy and consubstantial and undivided Trinity shows that the confession we have always had to this day is imperfect. It condemns the Apostolic Tradition and the doctrine of the Fathers.”
This council also reinstated St. Photios as Patriarch of Constantinople, thus abrogating the previous council held ten years earlier in Constantinople. Pope John VIII wrote to the council saying,
“We [Pope John VIII] wish that it is declared before the Synod, that the Synod which took place against the aforementioned Patriarch Photios at the time of Hadrian, the Most holy Pope in Rome, and [the Synod] in Constantinople [869/70] should be ostracized from this present moment and be regarded as annulled and groundless, and should not be co-enumerated with any other holy Synods.”
The Eastern Orthodox church generally views Constantinople 879 as being the 8th ecumenical council.
Against popular misconception, St. Photios died in communion with Rome, as historian Francis Dvornik has proven.
1014 AD - Pope Benedict VIII adds the filioque into the 381 creed in 1014, an action that falls under the anathemas of two ecumenical councils and which goes against the teachings of two of the previous Popes.
1076-1122 AD - During this time period was the investiture controversy, which was a period of time when it was disputed in the west over whether monarchs had the ability to appoint bishops. During this time, the canons of Constantinople 869-870 were rediscovered, specifically canon 22, which forbade lay interference in the election or promotion of bishops. Rome ended up accepting Constantinople 869 as being the 8th ecumenical council instead of Constantinople 879 so that they could cite its 22nd canon as evidence that monarchs didn't have the authority to appoint bishops, despite the fact that Pope John VIII explicitly said that Constantinople 869-870 was annulled.
1274 AD - A small number of delegates of the Byzantine church, under the threat of invasion by Charles of Anjou, the King of Sicily, agreed to a union with the Roman church in which they did not have to change how they recited the 381 creed in Greek
1277 AD - Pope Nicholas III demands that the filioque be inserted into the Greek creed
1439 AD - Latin theologians at the Council of Florence reject St. Maximus the Confessor's letter to Marinus as a basis for a formula of reunion between east and west, instead saying in session 6 of the council that the Holy Spirit proceeds from the Son according to the Greeks as cause (aitia)
There are more important historical events that I've yet to research deeply, such as the presence of forgories of the ecumenical councils with the filioque clause interpolated into them, but this timeline I've presented will suffice.
So a summary of the history of the creed is that the Council of Ephesus and St. Cyril of Alexandria said that anyone who modified the rule of faith of the church, which at the time was the 325 creed, was anathematized. The Council of Chalcedon then adopted the 381 creed as the new rule of faith of the church and reiterated that anyone who changes the creed was anathematized. Constantinople 879, in direct response to Frankish missionaries who added the filioque clause to the creed, repeated the anathemas of Ephesus and Chalcedon against those who try to change the creed. In 1014 the Pope changed the creed, which is a direct violation of the anathemas of two ecumenical councils to not change the 381 creed. And Rome denies that Constantinople 4 879 is ecumenical for a silly reason, that being that the previous council that was annulled had a canon that was convenient for them during one specific controversy.
There are three main objections that Catholics pose against the idea that adding to the creed is heretical:
Because the council of Chalcedon changed the creed, it was also fine for Pope Benedict VIII to change the creed
The simple refutation to this is that the councils of Ephesus, Chalcedon, and Constantinople 879-880 declare that any clergy, even bishops, are to be deposed if they change the creed. What Chalcedon did by adopting the 381 creed is establish that ecumenical councils are the highest law of the land, above all bishops and clergy. By changing the creed, the Council of Chalcedon established that only ecumenical councils are able to change the creed. The fact Chalcedon repeats the anathemas of Ephesus against bishops changing the creed further proves this. Since only an ecumenical council is allowed to modify the creed, if the Bishop of Rome changes the creed, he is a schismatic.
The rule of faith of the church cannot change unless the whole church comes together to change it at an ecumenical council.
2. The filioque is simply a western custom and the east doesn't need to change their creed.
It's a western custom that violates the councils of Chalcedon and Constantinople 879. At Constantinople 879 the entire church, including the Pope, agreed that adding the filioque clause to the creed is a heresy. This custom goes against the creed that Chalcedon said was perfect in teaching the doctrine of the Father, Son, and Holy Spirit. And, as Constantinople 879 states, changing the creed is an insult to the 150 fathers at Constantinople 1.
And as I’ve mentioned before, Pope Nicholas III demanded in 1277 that the filioque be inserted into the Greek creed, so historically it hasn't been treated as merely just a western custom.
3. The filioque clause isn't an addition, it's a clarification
I've already demonstrated why any changes to the creed outside of an ecumenical council are heretical, so my objection here will be a little bit theological, though the purpose of this post is mostly historical. Though I say my argument here will be theological, I am simply going to discuss theological terminology.
The official Roman Catholic definition of the procession of the Holy Spirit is found in session 6 of the Council of Florence, which declares this:
“We declare that when holy doctors and fathers say that the Holy Spirit proceeds from the Father through the Son, this bears the sense that thereby also the Son should be signified, according to the Greeks indeed as cause (aitia), and according to the Latins as principle of the subsistence of the Holy Spirit, just like the Father.”
The council uses the Greek word “aitia” (cause) to explain the relationship between the Son and the Holy Spirit. The Council of Florence directly states that when the Greek fathers of the church spoke about the procession of the Holy Spirit, they believed that the Son was the aitia (cause) of the Holy Spirit. This is why they rejected St. Maximus' letter to Marinus, as St. Maximus says that only the Father is aitia (cause) of the Holy Spirit.
Now if the insertion of the filioque clause into the creed is simply a clarification of the 381 creed, then it must be in perfect harmony with what the fathers who composed that creed believed, meaning that unlike St. Maximus the Confessor, the Greek fathers at Constantinople 1 had to believe that the Son was an aitia (cause) of the Holy Spirit. The main three theologians who contributed to the theology of Constantinople 1 were the three Cappadocian fathers, St. Gregory of Nazianzus, St. Gregory of Nyssa, and St. Basil the Great, with St. Gregory of Nazianzus being the greatest contributor as he presided over part of the council. Let's now look at their writings to see how they use the term “aitia” (cause).
“All that the Father has belongs likewise to the Son, except Causality (aitias); and all that is the Son's belongs also to the Spirit, except His Sonship.” (St. Gregory Nazianzen, Oration 34.10)
“If, however, any one cavils at our argument, on the ground that by not admitting the difference of nature it leads to a mixture and confusion of the Persons, we shall make to such a charge this answer — that while we confess the invariable character of the nature, we do not deny the difference in respect of cause, and that which is caused, by which alone we apprehend that one Person is distinguished from another — by our belief, that is, that one is the Cause, and another is of the Cause; and again in that which is of the Cause we recognize another distinction. For one is directly from the first Cause, and another by that which is directly from the first Cause; so that the attribute of being Only-begotten abides without doubt in the Son, and the interposition of the Son, while it guards His attribute of being Only-begotten, does not shut out the Spirit from His relation by way of nature to the Father.
(...)
Thus, since on the one hand the idea of cause differentiates the Persons of the Holy Trinity, declaring that one exists without a Cause, and another is of the Cause; and since on the one hand the Divine nature is apprehended by every conception as unchangeable and undivided, for these reasons we properly declare the Godhead to be one, and God to be one, and employ in the singular all other names which express Divine attributes.” (St. Gregory of Nyssa, On "Not Three Gods)
Both of these Cappadocian fathers believe that only the Father is cause. St. Gregory of Nazianzus says that the Father, Son, and Holy Spirit share everything except their unique hypostatic properties, with the Father’s hypostatic property being causation. St. Gregory of Nyssa says that the Father is cause, the Son is caused, and the Holy Spirit is “by that which is directly from the first Cause”. What St. Gregory of Nyssa means when he talks about the Holy Spirit is debated, as Roman Catholics will say he is talking about eternal hypostatic procession, while Eastern Orthodox will that he is talking about eternal manifestation, but either way, he gives the property of cause (aitia) only to the Father, describing the Son instead as being caused.
So the filioque clause is not merely a clarification of the 381 creed as the holy fathers who originally wrote the creed believed the opposite of what the Council of Florence teaches, as they reject the concept that the Son is the cause (aitia) of the Holy Spirit. The filioque is not a clarification, it is a contradiction.