The Angelic Doctor Against the Errors of the Greeks - Part Two - Chapter 27

That in the divine person to flow and to proceed is the same.

Again Cyril says in his explanation of the Nicene Creed: “The Spirit is coessential with the Father and the Son and flows forth, that is, proceeds from God and Father as from a source.”  From this it is established that in the divine persons to flow forth and to proceed are synonymous. The Holy Spirit flows forth from the Son as was demonstrated above;  therefore he proceeds from the Son.

This, moreover, is further confirmed by this statement he makes in his letter sent to Nestorious, namely, that “Christ is the truth and the Holy Spirit flows forth from him as he does from God and Father.”  If, therefore, to flow forth from the Father is the same as to proceed from him, from this that he flows from the Son he is shown to proceed from him.

Gregory Nazianzen also says in his sermon on the Epiphany: “Whence the Holy Spirit is, thence he proceeds.”  But, as has been proven, he is from the Son. Therefore, he proceeds from the Son. Cyril, too, says in his commentary on Joel: “The Holy Spirit belongs to Christ himself and is in him and from him, just as he is understood to be from God and Father.”  And Maximus the monk says in his sermon on the candlestick and the seven lights: “Just as the Holy Spirit naturally exists by God the Father according to his essence, so also he truly exists by the Son according to his nature and essence, as it were proceeding as God from the Father through the Son.” 

Likewise Athanasius in his letter to Serapion says: “As the Son is by nature related to the Father, so the Holy Spirit is related to the Son.”  And in the same letter, speaking in the person of the Son, he says: “The Spirit has the same nature and relationship toward me, the Son, so as to be God of God, as I have toward the Father so as to be God of God.”  Basil, too, against Eunomius says: “As the Son is related to the Father, so in the same way the Holy Spirit is related to the Son.”  But the Son is related to the Father as proceeding from him. For in John 8: 42 he says: I have proceeded and came from God. Therefore, the Holy Spirit proceeds from the Son.

But Epiphanius even uses the word procession in his book on the Trinity” “In the same way as no one knows the Father except the Son and no one knows the Son except the Father (Matt. 11:27), so I dare to say that no one knows the Holy Spirit except the Father and the Son from whom he receives and from whom he proceeds.”  And Athanasius on the Creed says: “The Holy Spirit is from the Father and the Son, not made, nor created, nor begotten, but proceeding.”