That the procession of the Holy Spirit from the Father and the Son is perfectly orthodox theology is seen in the fact that not only did Augustine teach it, but lots of great Fathers of the Church and theologians taught it for centuries after First Constantinople without any big objection from anybody.
The great work on the Trinity by Petavius (Lib. VII, cc. iii sqq.) develops the proof of this contention at length. Here we mention only some of the later documents in which the patristic doctrine has been clearly expressed:
- the dogmatic letter of St. Leo I to Turribius, Bishop of Astorga, Epistle 15 (447);
- the so-called Athanasian Creed;
- several councils held at Toledo in the years 447, 589 (III), 675 (XI), 693 (XVI);
- the letter of Pope Hormisdas to the Emperor Justius, Ep. lxxix (521);
- St. Martin I’s synodal utterance against the Monothelites, 649-655;
- Pope Adrian I’s answer to the Caroline Books, 772-795;
- the Synods of Mérida (666), Braga (675), and Hatfield (680);
- the writing of Pope Leo III (d. 816) to the monks of Jerusalem.
Some will reply that all these sources are from the Western Church. But the reality is that the Filioque was also compatible with the great Fathers of the Eastern Churches too:
- First, the Greek Fathers enumerate the Divine Persons in the same order as the Latin Fathers; they admit that the Son and the Holy Ghost are logically and ontologically connected in the same way as the Son and Father [St. Basil, Epistle 38; Against Eunomius I.20 and III, sub init.]
- Second, the Greek Fathers establish the same relation between the Son and the Holy Ghost as between the Father and the Son; as the Father is the fountain of the Son, so is the Son the fountain of the Holy Ghost (Athanasius, Ep. ad Serap. I, xix, sqq.; On the Incarnation 9; Orat. iii, adv. Arian., 24; Basil, Against Eunomius V; cf. Gregory of Nazianzus, Oration 43, no. 9).
- Third, passages are not wanting in the writings of the Greek Fathers in which the Procession of the Holy Ghost from the Son is clearly maintained: Gregory Thaumaturgus, “Expos. fidei sec.”, vers. saec. IV, in Rufinus, Hist. Eccl., VII, xxv; Epiphanius, Haer., c. lxii, 4; Gregory of Nyssa, Hom. iii in orat. domin.); Cyril of Alexandria, “Thes.”, as. xxxiv; the second canon of synod of forty bishops held in 410 at Seleucia in Mesopotamia; the Arabic versions of the Canons of St. Hippolytus; the Nestorian explanation of the Symbol.
All of these sources from both East and West in the centuries before the Great Schism are basically saying what the Filioque says: that the Holy Spirit proceeds from the Father and the Son.
But then sometime in the 700s, a local council in Spain did something momentous: they unilaterally inserted “and the Son” into the Creed, apparently in response to a local controversy which denied that the Spirit proceeded from the Son. In 796, we find another western bishop approving of this addition and finally a Council in Aachen approving it in 809. None of these were universally binding decisions representing the whole Church, but the Council in Aachen mattered for two reasons, one political and the other theological.
The political reason was that Aachen was the favorite city of the brand-new king of the brand-new Holy Roman Empire, Charlemagne. After the collapse of the Western Roman Empire in 476, all the power, money, and prestige of the old Roman Empire had become centered far to the East in Constantinople, where the Byzantine Emperor was (now Istanbul in modern-day Turkey). Western Christians were increasingly seen as the poor country cousins to the sophisticated and urban Eastern Church. But the Byzantine Empire had begun to suffer hits from the rise of Islam and various other political powers. So the coronation of Charlemagne as “Holy Roman Emperor” by the Pope himself on Christmas Day, 800 could not but be regarded as a threat by Byzantium, which saw itself as the sole heir and continuation of the Roman Empire. It made Charlemagne the first king of a united Western Empire—and a direct rival to the Emperor in Constantinople. Therefore, a Council held in Aachen could not but be seen as an affront to the Eastern Churches—which leads to the second, theological issue.
The Council of Aachen accepted the Filioque, but they also did what Christians had done since Paul vetted his gospel with Peter (Galatians 2:1-2) and the Council of Jerusalem made certain they were in union with Peter (Acts 15): they consulted the Pope, Leo III. Leo approved of the doctrine expressed by the Filioque, but suggested it nonetheless not be added to the Creed, precisely because he was sensitive to giving offence to the Eastern Churches.
Unfortunately, he was ignored by popular demand and the Filioque become popular and was sung more and more in various Churches in the West. By about 1015 (more than two centuries after Leo), the Pope himself regarded the wide popularity of the Filioque as an expression of the Spirit speaking through the Body of Christ and approved it for the liturgy in the Roman Church. Notably, this did not, in itself, trigger a schism with the Eastern Churches. It would take a span of time equal to the distance between the first election of Ronald Reagan to the present (2021 as of this writing) for Rome and Constantinople to finally excommunicate each other. But when the split finally came, the Filioque was the theological rationale for it in Constantinople.
Of which more on Monday.