That the Council of Florence teaches a heretical Pneumatology is as plain as the nose on one’s face. Articles on this subject tend to be very long, but this one will be short.
During the sixth session of the Council of Florence, the Roman Catholic Church dogmatized the meaning of the Filioque as follows:
In the name of the holy Trinity, Father, Son and holy Spirit, we define, with the approval of this holy universal council of Florence, that the following truth of faith shall be believed and accepted by all Christians and thus shall all profess it: that the holy Spirit is eternally from the Father and the Son, and has his essence and his subsistent being from the Father together with the Son, and proceeds from both eternally as from one principle and a single spiration. 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, and according to the Latins as principle of the subsistence of the holy Spirit, just like the Father.
And since the Father gave to his only-begotten Son in begetting him everything the Father has, except to be the Father, so the Son has eternally from the Father, by whom he was eternally begotten, this also, namely that the holy Spirit proceeds from the Son.
This does not mean all iterations of the Filioque are bad. The Filioque itself is found in several pre-schism writings of saints such as Augustine and Maximus the Confessor. So, the term in of itself is not automatically heretical (though it is certainly an extrabibilical gloss going beyond John 15:26). However, the meaning to the Filioque that Florence gives is clearly at variance with the pre-schism explanation of its meaning. This is evidenced by not only the explanation of Saint Maximus, but also the fact the Roman Catholic faction in Florence tentatively denied the authenticity of Maximus’ explanation–which is as follows:
Those of the Queen of cities have attacked the synodal letter of the present very holy Pope (Martin I), not in the case of all the chapters that he has written in it, but only in the case of two of them. One relates to theology, because it says he says that ‘the Holy Spirit proceeds (ἐκπορεύεσθαι) also from the Son.’…With regard to the first matter, they (the Romans) have produced the unanimous documentary evidence of the Latin fathers, and also of Cyril of Alexandria, from the sacred commentary he composed on the gospel of St. John. On the basis of these texts, they have shown that they have not made the Son the cause of the Spirit — they know in fact that the Father is the only cause of the Son and the Spirit, the one by begetting and the other by procession; but [they use this expression] in order to manifest the Spirit’s coming-forth (προϊέναι) through Him [the Son] and, in this way, to make clear the unity and identity of the essence (Letter to Marinus).
What Saint Maximus is speaking of is pretty simple and it is clearly the stance of the Orthodox Catholic, as opposed to the Roman Catholic, Church. In Florence, the Roman Catholics, though having the copy of the letter in a pro-Filioque florilegium, would disown the letter explicitly because they disagreed with its content:
When presented with the testimony of the letter from the Latin side, the Greeks jumped at the opportunity to offer union on its basis: “If this letter is accepted gladly on your part,” so they are reported to have said, “the union will happily proceed.” At this the Latin delegation chastened Andrew [of Rhodes] and denied their willingness to admit the letter for any purpose on the grounds that it was “not found to be complete.”
Twice more, in the course of debates over the orthodoxy of the Filioque, during which it appeared to the Greeks at times that the Latins were saying substantively the same things as the letter, they offered the wording of the Letter to Marinus as a formula for union (irrespective of whatever inherent authority it might have). They were rebuffed on both occasions (Chapter by Fr. Jacob van Sickle).
Unlike Florence, which explicitly denied Maximus’ doctrine of the Filioque, we Orthodox have actually dogmatized his thought. The Council of Blachernae (1285) stated succinctly in its fourth and fifth anathemas against John Bekkos:
In certain texts [of the Fathers], the phrase [“through the Son”] denotes the Spirit’s shining forth and manifestation. Indeed, the very Paraclete shines from and is manifest eternally through the Son, in the same way that light shines forth and is manifest through the intermediary of the sun’s rays; it further denotes the bestowing, giving, and sending of the Spirit to us. It does not, however, mean that it subsists through the Son and from the Son, and that it receives its being through Him and from Him….According to the common mind of the Church and the aforementioned saints, the Father is the foundation and the source of the Son and the Spirit, the only source of divinity, and the only cause.
This exegesis of Pneumatological doctrine is not some sort of outlier, because it was both implied by Maximus and explicitly taught by Saint John of Damascus. The Damascene’s writings were employed by Roman Catholic progenitors of the Councils of Lyon and Florence, but they were not relying upon reliable sources. “[During Florence] both parties often relied on preexisting anthologies (florilegia) that comprised the crucial passages of a work, the textual accuracy of which was never guaranteed,” according Alexander Alexakis (p. 154). “To quote only one example, the quality of most quotations included in the Pro-Union collection of about 300 testimonia called Epigraphai of John Vekkos (patriarch of Constantinople between 1276-1282) is very poor.”
In short, there appeared to be no serious interaction with John’s thought during Florence. A careful reading of the Damascene’s Exposition of the Orthodox Faith reveals to us how thoroughly he taught the Pneumatological doctrine we see in Blachernae:
Likewise we believe in the Holy Spirit…in all things like to the Father and Son: proceeding from the Father and communicated through the Son, and participated in by all creation, through Himself creating, and investing with essence and sanctifying, and maintaining the universe: having subsistence, existing in its own proper and peculiar subsistence, inseparable and indivisible from Father and Son, and possessing all the qualities that the Father and Son possess, save that of not being begotten or born. For the Father is without cause and unborn: for He is derived from nothing, but derives from Himself His being, nor does He derive a single quality from another. Rather He is Himself the beginning and cause of the existence of all things in a definite and natural manner. But the Son is derived from the Father after the manner of generation, and the Holy Spirit likewise is derived from the Father, yet not after the manner of generation, but after that of procession. And we have learned that there is a difference between generation and procession, but the nature of that difference we in no wise understand. Further, the generation of the Son from the Father and the procession of the Holy Spirit are simultaneous. All then that the Son and the Spirit have is from the Father, even their very being.
…And we speak likewise of the Holy Spirit as from the Father, and call Him the Spirit of the Father. And we do not speak of the Spirit as from the Son : but yet we call Him the Spirit of the Son. For if any one has not the Spirit of Christ, he is none of His Romans 8:9, says the divine apostle. And we confess that He is manifested and imparted to us through the Son. For He breathed upon His Disciples, says he, and said, Receive the Holy Spirit. John 20:29 It is just the same as in the case of the sun from which come both the ray and the radiance (for the sun itself is the source of both the ray and the radiance), and it is through the ray that the radiance is imparted to us, and it is the radiance itself by which we are lightened and in which we participate. Further we do not speak of the Son of the Spirit, or of the Son as derived from the Spirit. (Exposition, Book I, Chap 8).
All the terms, then, that are appropriate to the Father, as cause, source, begetter, are to be ascribed to the Father alone: while those that are appropriate to the caused, begotten Son, Word, immediate power, will, wisdom, are to be ascribed to the Son: and those that are appropriate to the caused, processional, manifesting, perfecting power, are to be ascribed to the Holy Spirit. The Father is the source and cause of the Son and the Holy Spirit: Father of the Son alone and producer of the Holy Spirit…And we speak also of the Spirit of the Son, not as through proceeding from Him, but as proceeding through Him from the Father. For the Father alone is cause (Ibid., Chap 12).
In summary, the Son and Spirit have different modes of eternal causation (one via being begotten and the other procession) and that both modes are alone caused by the Father. The existence of the hypostasis of the Spirit is not contingent upon the Son, but (instead) He manifests through the Son–just as the radiance of the sun is manifested in a sun ray, but the sun ray does not cause radiance. The sun is the sole source of radiance.
Before concluding this article about how the Filioque of Florence is heretical, it is worth pointing out that it explicitly contradicts the Second Council of Nicea. Therein, Saint Tarasius in his confession during the third session states that the Holy Spirit “proceedeth from the Father by the Son.” Taking into account contemporary Greek Pneumatology, it would seem that the statement must be understood consistently with the “manifestation” doctrine of the Spirit as laid out by John of Damascus. Tarasius’ statement, perhaps not making sense in Latin (especially without John’s explanation being available in Latin), went right over the heads of the forefathers of future Latin Christendom–both the Carolinigan theologians and Pope Adrian I (see footnotes in pages 91-93).
The Carolingians read the statement to mean that the Spirit was caused by some separate event by the Son and therefore made the Spirit of a different essence. Pope Adrian I responded with the assertion that the Son and Spirit both proceed from the Father and therefore (I suppose) they share the same essence. It seems that Pope Adrian I gets closer to the truth. Through some game of multi-lingual telephone, the idea that the Son and Spirit both proceed from the Father is somewhat similar to the ray and radiance both originating from the sun. In short, Adrian betrays some grasp of the Greek manifestation doctrine of the Spirit, but uses technically incorrect language.
Nevertheless, he ham-handled the word “proceed” and so the Orthodox doctrine of the Spirit’s procession was further obfuscated in the West among theologians who clearly did not understand the point at issue. Sadly, these ancestors would pass on their hazy ideas to the scholastics, the men who thoroughly devised and systematized the modern Filioque doctrine.
For a brief argument that the pre-schism Filioque of Latin saints was Orthodox (and therefore not “hazy” as it would later prove to be), check out this post from Shameless Orthodoxy.