Five Ecumenical Councils approved a letter of Patriarch St. Cyril of Alexandria that taught the Dogma of the Filioque!
Cardinal St. Robert Bellarmine gives a manifest proof establishing the doctrine from the authority of five ecumenical councils:
Omitting these things, then, let us bring forward the Councils that testify the Holy Spirit proceeds from the Son. First the Council celebrated at Alexandria, from which Council Cyril writes a letter to Nestorius in which are these words, ‘The Spirit is called the Spirit of Truth, and Christ is Truth, and so He proceeds from Him likewise as from the Father.’ This letter was read in the Council of Ephesus and was approved both by the Council of Ephesus itself and by the fourth Synod, and by the fifth Synod and by the sixth and seventh Synods. We have therefore five general Councils celebrated among the Greeks which receive the most open and clear opinion that the Holy Spirit proceeds from the Son as from the Father. What then do they now seek? What do they demand?
Patriarch St. Cyril and the five ecumenical councils mentioned by Cardinal St. Robert Bellarmine give us the patristic and Church-authorized interpretation of the Word of Christ in Sacred Scripture. As we will see subsequently, Bishops like St. Hilary, St. Ambrose, and St. Augustine had already done this in the West in the 4th century.
 Greek Orthodox Bishops and Patriarchs, at Nicene Ecumenical Councils, confess doctrine practically equivalent to the Filioque.
As if that were not enough, we have the testimony of two Eastern saintly bishops, one of whom was patriarch of the Greek Church and made a dogmatic confession.
Bp. St. Leontius of Caesarea, at Nicaea I, testifies that “the Spirit proceeds from the Father, and is proper to the Son and gushes forth from Him” . This is the Faith of the 318 fathers gathered at Nicaea. As Cardinal St. Robert writes, it was not explicitly defined in Nicaea, because the necessity had not yet arisen, as the ancient fathers testified, “I for my part cannot sufficiently wonder with what boldness Jeremias, who calls himself Ecumenical Patriarch, dared to write recently in his censure of the confession of the Lutherans that it was defined by the Synod of Nicaea and all subsequent general Councils that the Holy Spirit proceeds from the Father alone[.] … Let us then consult the Nicene Creed, and let us see whether it teaches in very expressive words that the Holy Spirit proceeds from the Father alone. The whole Nicene Creed is cited by Cyril among the Greeks, by Ruffinus among the Latins, but nothing else is read in that Creed about the Holy Spirit than this opinion ‘and [I believe] in the Holy Spirit.’ Now Nazianzen testifies that the Nicene Synod did not hand on the perfect doctrine about the Holy Spirit for the reason that the question about the Holy Spirit had not arisen. Let Jeremias see in which Nicene Creed he has read that the Holy Spirit proceeds from the Father alone.”
Patriarch St. Tarasius of Constantinople, at Nicaea II, declared, in the Creed, “And in the Holy Spirit, the Lord and Giver of Life, Who Proceeds from the Father through the Son, and is acknowledged to be Himself God” . Just as the 150 fathers at Constantinople I added to the Creed of Nicaea the words, “the Lord and Giver of Life, Who Proceeds from the Father,” etc., Patriarch St. Tarasius here adds the words “through the Son,” etc. This shows the Faith of the Universal Church at Nicaea II.
 Great Latin bishops and fathers exegete and interpret the words of Sacred Scripture in favor of the Filioque doctrine.
Bishop St. Hilary of Poitiers says it is one and the same thing to proceed from the Father, receive from Him and from His Son:
Now I ask whether to receive from the Son is the same thing as to proceed from the Father. But if one believes that there is a difference between receiving from the Son and proceeding from the Father, surely to receive from the Son and to receive from the Father will be regarded as one and the same thing. For our Lord Himself says, Because He shall receive of Mine and shall declare it unto you. All things whatsoever the Father has are Mine: therefore said I, He shall receive of Mine and shall declare it unto you. That which He will receive — whether it will be power, or excellence, or teaching — the Son has said must be received from Him, and again He indicates that this same thing must be received from the Father. For when He says that all things whatsoever the Father has are His, and that for this cause He declared that it must be received from His own, He teaches also that what is received from the Father is yet received from Himself, because all things that the Father has are His. 
Our Lord Jesus teaches about this in detail in Gospel of St. John, chapters 14–16. The Lord Himself, the apostles, and the fathers, explain that the Spirit proceeds from the Son.
Bishop St. Ambrose says St. John was a witness even in Heaven that the Holy Spirit proceeds from the Father and the Son :
53. And this, again, is not a trivial matter that we read that a river goes forth from the throne of God. For you read the words of the Evangelist John to this purport: And He showed me a river of living water, bright as crystal, proceeding out of the throne of God and of the Lamb. In the midst of the street thereof, and on either side, was the tree of life, bearing twelve kinds of fruits, yielding its fruit every month, and the leaves of the tree were for the healing of all nations (Revelation 22:1–2). 154. This is certainly the River proceeding from the throne of God, that is, the Holy Spirit, Whom he drinks who believes in Christ, as He Himself says: If any man thirst, let him come to Me and drink. He that believes in Me, as says the Scripture, out of his belly shall flow rivers of living water. But this spoke He of the Spirit. (John 7:37-38) Therefore the river is the Spirit. 
Such an amazing testimony hidden in the Sacred Scriptures should fill us with amazement. It is the Holy Spirit Himself Who assures us whence He proceeds.
Bishop St. Augustine says Jesus breathed forth the Holy Spirit to show that the Holy Spirit proceeds from the Son. St. Augustine has written much on the Filioque.
St. Augustine says Jesus bears witness to Filioque in countless ways:
And it is proved by many other testimonies of the Divine Word, that the Spirit, who is specially called in the Trinity the Holy Spirit, is of the Father and of the Son: of whom likewise the Son Himself says, Whom I will send unto you from the Father; and in another place, Whom the Father will send in my name. And we are so taught that He proceeds from both, because the Son Himself says, He proceeds from the Father. And when He had risen from the dead, and had appeared to His disciples, He breathed upon them, and said, Receive the Holy Ghost, so as to show that He proceeded also from Himself[.] … Wherefore let him who can understand the generation of the Son from the Father without time, understand also the procession of the Holy Spirit from both without time. And let him who can understand, in that which the Son says, As the Father has life in Himself, so has He given to the Son to have life in Himself, not that the Father gave life to the Son already existing without life, but that He so begot Him apart from time, that the life which the Father gave to the Son by begetting Him is co-eternal with the life of the Father who gave it: let him, I say, understand, that as the Father has in Himself that the Holy Spirit should proceed from Him, so has He given to the Son that the same Holy Spirit should proceed from Him, and be both apart from time: and that the Holy Spirit is so said to proceed from the Father as that it be understood that His proceeding also from the Son, is a property derived by the Son from the Father. For if the Son has of the Father whatever He has, then certainly He has of the Father, that the Holy Spirit proceeds also from Him. But let no one think of any times therein which imply a sooner and a later; because these things are not there at all. How, then, would it not be most absurd to call Him the Son of both: when, just as generation from the Father, without any changeableness of nature, gives to the Son essence, without beginning of time; so procession from both, without any changeableness of nature, gives to the Holy Spirit essence without beginning of time? 
A testimony so clear as this should suffice to put an end to the later heresy of Photian Monopatrism once and for all.
 Byzantine and Eastern fathers and monks testify that the spiration of the Spirit from the Father does not exclude but rather is mediated through the Son.
St. Basil the Great states that the Holy Spirit is united through the Word in the eternal unity of the Holy Trinity: “Through the Son, who is one, he is joined to the Father, who is one, and by himself completes the Blessed Trinity” . The Son is One, the Father is One, the Spirit is One united to the Father through the Son.
St. Maximus the Confessor said: “By nature the Holy Spirit in his being takes substantially his origin from the Father through the Son who is begotten” . The Holy Spirit takes His being substantially from the Father through the Son, and this in such a way that the Father gave the Spirit to the Son in eternally begetting Him.
St. John Damascene is the sole saint cited as possibly denying the Filioque, yet even he does not deny that the Trinitarian Order has the Spirit always issuing from the Father through the Word: “I say that God is always Father since he has always his Word coming from himself, and through his Word, having his Spirit issuing from him” .
We have seen that St. Tarasius dogmatized such a profession at the Second Nicene Council, the seventh ecumenical council. This is the true tradition of the fathers.
 The Latin fathers are absolutely unanimous in teaching the doctrine of the Filioque. Bishops and several councils do the same.
This is a fact so clear that it will hardly be doubted. It is explicitly stated by St. Maximus , and further evidence for the same can be read in Dr. Henry Barclay Swete’s monumental work on the subject . The evidence documented in point  already establishes this, and in St. Robert’s treatise, the doctor explicitly cites much proof; but we will cite the Athanasian Creed, which even secular scholars do not doubt was the widely accepted faith of the Western Church by at least the 5th century.
As St. Robert adduces it, “[b]lessed Athanasius who says in his Creed, ‘The Holy Spirit is not made nor created nor generated by the Father and the Son, but proceeds.'”
To this testimony an objection might be made — namely, that this creed is not really from Athanasius. This is easily refuted, both by Nazianzen, where he says in praise of Athanasius that he composed a most perfect confession of faith that the whole West and East venerate, and also from Augustine, who by name cites Athanasius, bishop of Alexandria and adduces a complete section of this creed, and he uses whole sentences from it, with the name of Athanasius, as if it were well known in the Church.
The Third Council of Toledo (589) is also evidence of the universal acceptance of this doctrine: “Credo in Spiritum Sanctum qui ex patre filioque procedit” (I believe in the Holy Spirit Who Proceeds from the Father and the Son). Both Archbishop St. Leander of Seville, who presided, and his brother, St. Isidore, teach the Filioque dogma.
 The Greek Fathers are unanimous in teaching the doctrine “per Filium” (through the Son). This fact has been found embarrassing by deniers of the Filioque.
Philip Schaff, in History of the Christian Church, says, “Photius and the later Eastern controversialists dropped or rejected the per Filium, as being nearly equivalent to ex Filio or Filioque, or understood it as being applicable only to the mission of the Spirit, and emphasized the exclusiveness of the procession from the Father . “The teachings of St. Basil and St. Maximus shown earlier, and especially the profession of St. Tarasius at Nicaea II, demonstrate that per Filium is dogma.
 The Roman pontiffs, the successors of St. Peter, have unanimously taught the Filioque explicitly for millennia. There is clear unbroken tradition present here.
Pope St. Damasus, quite likely in a synod before the year 380 A.D., used the Filioque in a response to the Macedonian heresy: “We believe … in the Holy Spirit, not begotten nor unbegotten, not created nor made, but proceeding from the Father and the Son, always co-eternal with the Father and the Son” .
Note the special value of this ancient testimony of the 4th-century Roman Church, world-renowned for its Catholic orthodoxy and defense of St. Athanasius contra mundum under Pope St. Julius, et al. It is incidental and undesigned. It presupposes the dogmatic truth of the Filioque in a controversy against Macedonian heretics (who blasphemed against the Divinity of the Holy Spirit). And it shows that the dogma of the Holy Spirit’s divinity is no less certain than the dogma of the Filioque.
Another 4th-century Roman synod states: “The Holy Spirit is not only the Spirit of the Father, or not only the Spirit of the Son, but the Spirit of the Father and the Son. For it is written, ‘If anyone loves the world, the Spirit of the Father is not in him’ (1 Jn. 2:15). Likewise, it is written, ‘If anyone, however, does not have the Spirit of Christ, He is none of His (Romans 8:9).’ When the Father and the Son are mentioned in this way, the Holy Spirit is understood, of whom the Son Himself says in the Gospel, that the Holy Spirit ‘proceedeth from the Father (John 15:26)’ and ‘He shall receive of mine and shall annuonce it to you (Jn. 16:14)'” .
Are there more such testimonies from the ancient orthodox Roman Church? Yes: Pope St. Leo the Great, in the 5th century, says, “And so under the first head is shown what unholy views they hold about the Divine Trinity: they affirm that the person of the Father, the Son, and the Holy Ghost is one and the same, as if the same God were named now Father, now Son, and now Holy Ghost: and as if He who begat were not one, He who was begotten another, and He who proceeded from both yet another” .
This letter of Pope St. Leo I is cited in the Catechism of the Catholic Church. Is there another Pope, saint, and great who teaches Filioque? Yes: Pope St. Gregory the Great in the 6th century shows the dogmatic Roman and universal tradition when he confesses, “We can also understand His being sent in terms of His divine nature. The Son is said to be sent from the Father from the fact that He is begotten of the Father. The Son relates that He sends the Holy Spirit[.] … The sending of the Spirit is that procession by which He proceeds from the Father and the Son. Accordingly, as the Spirit is said to be sent because it proceeds, so too it is not inappropriate to say that the Son is sent because He is begotten” . This statement shows that, contra the Greeks, sending reveals hypostatic relation. That is why, throughout the Holy Scriptures, we never read that the Father is sent. The Father does not proceed from anyone. The Son proceeds from the Father alone, by generation, therefore He is said to be sent by the Father. The Spirit proceeds from the Father and the Son, therefore the Son explicitly says many times, “But I tell you the truth: it is expedient to you that I go: for if I go not, the Paraclete will not come to you; but if I go, I will send him to you” (Jn. 16:7) that we may understand the eternal relation implied here.
3 Objections of the Greek Church and a brief response to them — is the Filioque doctrine true, certain, established from Scripture, fathers and the early councils?
Objection I: It seems the texts cited refer not to the eternal procession of the Holy Ghost, but to His temporal mission — i.e., He is sent by the Son only in time.
This is an expected objection — one the texts themselves anticipate and answer. When the Fathers say (1) the Father gave it to the Son, in begetting Him, that the Holy Spirit proceeds from Him, they show that the procession from the Father through the Son is eternal as the generation of the Son is eternal. (2) When the Fathers say He proceeds from the Father just as He proceeds from the Son, they show that just as the procession from the Father is eternal, so it is from the Son.
Objection II: Even if the Holy Spirit’s eternal procession from the Father is mediated through the Son, it doesn’t seem to follow that He proceeds through the Son. It could be that it is merely His energetic manifestation that happens through the Son, but not that His divine hypostasis receives essence from Father through Son.
There are only two processions in the Holy Trinity, using “procession” in a broad sense (as both St. Augustine and St. Cyril do) to explain it.
(1) The eternal procession specifically called generation, by which the Person of the Father is distinguished from the Person of the Son, so that He Who begat is one Person, and He Who is begotten is another. (This second objection is almost like someone saying the Son’s hypostasis is not eternally begotten of the Father.)
(2) And the eternal procession specifically called spiration, by which the Person of the Holy Spirit is distinguished from both the Person of the Father and the Person of the Son. For He from Whom He proceeds is One Person, He through Whom He proceeds is the Second Person, and He Who proceeds is the Eternal Third Person.
This is the sense in which Pope St. Leo the Great explains it in the source cited above. Since the hypostases are distinguished, it is clearly hypostatic procession.
The answer to energetic procession is as follows: there is only One Grace and One Energy of the Three Divine Persons. For, e.g., the Grace of the Holy Spirit is not distinct from the Grace of the Son, but is identical to it. Therefore, when Son and Spirit are distinguished, as by St. Cyril, it must be Persons Who are spoken of.
Objection III: But the Greek Fathers say that the Father is the Sole Cause, the Unoriginate Source of the Triune Godhead, what the Latin Fathers call the Monarch of the Holy Trinity. It seems, then, either that this teaching of the Greek Fathers must be rejected in light of the dogmatic Tradition or the Tradition must be false.
No, not at all. Just as the Greek Fathers say the Eternal Father is the sole Unoriginate Source of the Godhead, the Latin Fathers say the Eternal Father is the Sole Principle without Principle in the Godhead. Thus St. Augustine, cited by St. Thomas: “The Father is the Principle of the Whole Deity.” Texts from the Council of Florence and from the Catechism of the Catholic Church have explained this in more detail. The Father gives His Son His Spirit eternally, so the Holy Spirit is eternally the Spirit of both the Father and the Son, but the Father remains sole principle without principle, since the Son receives from the Father all that He has.
So the difficulties are resolved, and there is no need to reject any teaching of either the Greek or the Latin Fathers. The only thing necessary here for all who seriously and sincerely study the matter (besides to pray much to the Holy Trinity and especially ask the Holy Ghost for His Gifts to understand it) is to have the strong and unshakeable conviction of Catholic Faith: all the Latin Fathers, and all the Greek Fathers, no matter what, cannot collectively be mistaken. This should be a truth almost of faith for us, somewhat similar to how we would never admit the OT contradicts the NT, or the Gospels contradict the Epistles. There must, if an apparent discrepancy arises, be in fact a perfectly fine harmonization of the two apparently different approaches, which further prayer and study will indicate to us.
2 Final Objections from the disciplinary aspect are considered — even if the Filioque doctrine is true, is it good and acceptable to profess it in the Creed?
Objection IV: But the Council of Ephesus says we shouldn’t add to the Creed. We even know that Patriarch St. Cyril professed the Creed of Nicaea during that Council.
Correct to the second part. And if the fathers at Ephesus meant that nobody should add any word to the Creed, even to more fully explain apostolic doctrine, then the 150 fathers of Constantinople would have been anathema, for, as seen above, they added the words “The Lord and Giver of Life,” etc. — which is evidently absurd. The fact that the ancient Church received the Creed of Constantinople as complementary and as a beautiful exposition of doctrine already implied in the Nicene Creed shows that the mind of the early Church was not only not opposed to, but even welcomed such more explicit dogmatic definitions of Church doctrine. Moreover, Patriarch St. Tarasius adopted the Creed to profess more explicitly the dogma “per Filium” of the Greek Fathers in the Second Nicene Ecumenical Council. We have already seen also that, before Rome accepted the Nicene-Constantinopolitan Creed, Rome had already professed the dogma of the Filioque, confessing the Holy Spirit proceeds from Father and Son. Both Pope St. Damasus I and Pope St. Leo I, among several other Roman pontiffs, explicitly professed it. The Creed of St. Athanasius taught it. When Photius invented his Monopatrite theory, that the Holy Spirit proceeds from the Father to the exclusion of the Son, it became necessary to profess the dogma more explicitly against that heresy. Later on, many Eastern churches professed the dogma and became Catholic but were not always required to profess it in the Creed.
Objection V: Granting that the Creed could be elaborated on to explain a dogma more deeply, shouldn’t this be done at an ecumenical council of both Greeks and Latins?
Since the pope added it to the Latin Creed only, and since without doubt the pope is the patriarch of the Latin Church, it doesn’t seem that there should have been an issue. But certainly, it could be done and has been done; that’s why the dignitaries of both the Greek and Russian Churches, as well as of Syrian and Oriental Churches, and the Armenian Apostolic Church, were invited to the Second Council of Lyons and the Council of Florence to come together with the Catholic Church and jointly accept the Profession of Faith of the Universal Church. But whatever the past may have been, Pope Francis and Patriarch Bartholomew have invited all Christians to gather together in 2025 at Nicaea, to commemorate its 1,700th anniversary. Therefore, by God’s Grace, Greek and Latin Churches can once more profess dogma together.
The solution adopted by Greek and Latin bishops and theologians from a few decades ago was this:
The Father only generates the Son by breathing (proballein in Greek) through him the Holy Spirit and the Son is only begotten by the Father insofar as the spiration (probolh in Greek) passes through him. The Father is Father of the One Son only by being for him and through him the origin of the Holy Spirit. The Spirit does not precede the Son, since the Son characterizes as Father the Father from whom the Spirit takes his origin, according to the Trinitarian order. But the spiration of the Spirit from the Father takes place by and through (the two senses of dia in Greek) the generation of the Son, to which it gives its Trinitarian character.
And thus, the solution to both the dogmatic and disciplinary difficulties should be clear. The only question now is whether the will to reunite is present or not.
In Conclusion: A call to our separated brethren in the Eastern Orthodox churches to return soon to holy union with the One, Holy, Catholic and Apostolic Church.
Dear Orthodox Christians: A word from our hearts to yours — if we wish Christianity to successfully combat and entirely overcome the new paganism of the culture of death, of abortionism, contraception, divorce, pornography, and other forms of immorality and lawlessness, if we hope for the worldwide Church to receive more conversions from paganism and baptize more individuals into Christ and the Triune God, and make them members of the Church, the time to reunite is now and quickly.
The Immaculate Heart of Mary, the first defender of Christian civilization, alone warned the world about the dangers and errors of communism and the great persecutions threatening the Church and all Christendom. The history of the last century bears sad testimony to the truth of her words and the urgency of her calling. The time is ripe and the hour is now for the Greek and Russian Orthodox churches to profess the Filioque dogma and unite with the Catholic Church for the glory of God.
The world cannot resist the power and grace of a reunited Christendom. Victories in the pro-life movement, victories against Christian persecution, against Islamism, communism, and secularism await us. We have every reason to believe and hope Almighty God will Himself lead the effort to bring the Eastern Orthodox back to the Catholic Church, and His action will give the greatest impetus to world evangelism as has scarcely been seen since the first day of Pentecost. Deus vult. God wills it.
Also foretold in sacred Scripture is the return of the Jewish people to the Faith and to the Church of Jesus Christ. It is inconceivable that Christendom will not be visibly united by the time this happens, and that full reunion would be a glorious preparation for this glorious impending event.
May all Christians of East and West no longer be divided along sectarian lines and national or other denominations, but become One in the Universal or Catholic Church. And this so that, as the Scripture says, the whole world may believe that Jesus Christ is the Lord, and has been sent by the Father for the salvation of us all. “That they all may be one, as thou, Father, in me, and I in thee; that they also may be one in us; that the world may believe that thou hast sent me” (Jn 17:21).
It would be ideal for popes and patriarchs to meet often, and for faithful Catholics and lay Orthodox to petition them for reunion. This would bring peace to the world and unity to Christendom and gladden the Heart of God so severely pierced. And thus we will welcome, with as minimal tribulation as reasonably possible, the reign of the Sacred Heart of Jesus and the triumph of the Immaculate Heart of Mary.
 Third Letter of St. Cyril to Nestorius, from an Orthodox source: https://orthodoxjointcommission.wordpress.com/2013/12/14/st-cyrils-third-letter-to-nestorius/
See St. Cyril of Alexandria: Aeterna Press for the Greek text and for other places where the Saintly Patriarch of Alexandria develops the same doctrine.
 St. Robert Bellarmine, On the Procession of the Holy Spirit from the Son: http://www.catholicapologetics.info/apologetics/protestantism/procession.htm
 Mansi II:868CD. Bishop St. Leontius of Caesarea was the personal friend of St. Gregory the Illuminator, the Apostle of Armenia.
 Mansi, XII, 1122 D. The Greek is transliterated “to Pneuma to agion, to kurion kai zwopoion, to ek tou Patros dia tou Uiou ekporeuomenon.”
 In Patrologia Latina, the reference is PL-10:250C-251A
 On the Holy Spirit, Book III, p. 153–154. Credit to Catholic Nick for this: http://catholicnick.blogspot.com/2011/12/filioque-proved-in-revelation-221.html.
 St. Augustine, De Trinitate, Book 15, Ch. 26
 Treatise on the Holy Spirit, XVIII, 45, Sources chrétiennes 17 bis, p. 408
 Quaestiones ad Thalassium, LXIII, PG 90, 672 C
 Dialogus contra Manichaeos 5, PG 94, 1512 B, ed. B. Kotter, Berlin 1981, p. 354; cf. PG 94, 848-849 A
 Ad Domnum Marinum Cypri presbyterum (Letter to the priest Marinus of Cyprus), PG 91, 134D–136C
 Swete, H.B. On The History Of The Doctrine Of The Procession Of The Holy Spirit: From The Apostolic Age To The Death Of Charlemagne
 Schaff, Philip. History of the Christian Church. (1885)
 The Filioque: History of a Doctrinal Controversy, A. Edward Siecienski, pp. 56–57
 Patrologia Latina 13.374
 Cf. Leo I, Quam laudabiliter (447): DS 284
 Homiliarium in Evangelia Libri Duo 2.26 (Eng. Trans. Gregory the Great, Forty Gospel Homilies, trans. Dom David Hurst, page 202)
 The Greek and Latin Traditions regarding the Procession of the Holy Spirit: Study from the Pontifical Council for Promoting Christian Unity