Book Four — Salvation, Chapter 24 — Summa Contra Gentiles
[1] We find some who make this mistake about the procession of the Holy Spirit: they say the Holy Spirit does not proceed from the Son. For this reason we must show that the Holy Spirit does proceed from the Son.
[2] It is manifest in sacred Scripture that the Holy Spirit is the Spirit of the Son, for Romans (8:9) says: “If any man have not the Spirit of Christ, he is none of His.” But that one might not be able to say that the Spirit that proceeds from the Father is one, and the Son’s Spirit another, it is shown from the words of the same Apostle that the Holy Spirit of the Father and of the Son is identified. For the words just cited, “If any man have not the Spirit of Christ, he is none of His,” the Apostle added after he had said: “If so be that the Spirit of God dwell in us,” and so forth. But one cannot say that the Holy Spirit is the Spirit of Christ merely because He had Him as man, according to the words of Luke (4:1): “Jesus being full of the Holy Spirit, returned from the Jordan.” For one reads in Galatians (4:6): “Because you are sons, God has sent the Spirit of His Son into your hearts, crying: Abba (Father).” The Holy Spirit, therefore, makes us the sons of God precisely because He is the Spirit of the Son of God. But we are made the adoptive sons of God by assimilation to the natural Son of God, as Romans (8:29) has it: “Whom He foreknew, He also predestined to be made conformable to the image of His Son, that He might be the firstborn amongst many brethren.” Thus, then, is the Holy Spirit the Spirit of Christ: so far as He is God’s natural Son. But there is no relation in accord with which the Holy Spirit can be called the Spirit of the Son of God except a relation of origin, for this is the only distinction we find in divinity. Therefore, one must say that the Holy Spirit is the Son’s Spirit by proceeding from Him.
[3] The Holy Spirit, again, is sent by the Son; consider John (15:26): “When the Paraclete cometh, whom I will send you from the Father.” But whoever sends has an authority over the one sent. One must, then, say that the Son has an authority in regard to the Holy Spirit: not, of course, that of being master or being greater, but in accord with origin only. In this wise, then, the Holy Spirit is from the Son. Now, let one say that the Son is sent by the Holy Spirit as well, because we read in Luke (4:18-21) that our Lord said Isaiah’s words (61:1) were fulfilled in Him: “The Spirit of the Lord is upon Me, He has sent Me to preach the gospel to the poor.” But consideration must be given this: the Son is sent by the Holy Spirit in accord with the assumed nature. But the Holy Spirit has not assumed a created nature, so that in accord with it He can be called sent by the Son, or so as to give the Son authority in His regard. Therefore, this remains: it is considered as an eternal person that the Son has authority over the Holy Spirit.
[4] There is more. In John (16:14-15), the Son says of the Holy Spirit: “He shall glorify Me because He shall receive of Mine.” Of course, this cannot be said: He receives what is the Son’s, but does not receive from the Son; by saying, for instance, that He receives the Son’s divine essence from the Father. Hence, our Lord adds: “All things whatsoever the Father has are mine. Therefore, I said that He shall receive of Mine.” For, if all things which are the Father’s are the Son’s as well, the Father’s authority as principle of the Holy Spirit must be the Son’s as well. Therefore, just as the Holy Spirit receives what is the Father’s from the Father, so He receives what is the Son’s from the Son.
[5] Here one can also introduce the testimonies of the Doctors of the Church, the Greeks included. Athanasius says: “The Holy Spirit is from the Father and the Son-not made, not created, not begotten, but proceeding.” Cyril, too, in his epistle received by the Council of Chalcedon, says: “The Spirit of the truth is named and is the Spirit of the Truth and flows from Him just as, indeed, from God the Father.” Didymus also says in his book On the Holy Spirit: “The Son is nothing else than what is given to Him by the Father, and the substance of the Holy Spirit is no other than that given Him by the Son.” Of course, it is ridiculous that some concede that the Holy Spirit “is from the Son” or “flows from the Son” but does not “proceed from. Him.” For the verb “to proceed,” among all those which refer to origin, turns up most commonly; for, if anything is in any way at all from something, we say it proceeds from that thing. And since divinity is better designated by what is common than by what is special, in the origin of the divine persons the verb proceeding is the most suitable. And so, if one concedes that the Holy Spirit “is from the Son” or “flows from the Son,” it follows that “He proceeds from the Son.”
[6] There is this, too, in the determination of the Fifth Council: “In all matters we follow the holy Fathers and Doctors of the Church: Athanasius, Hilary, Basil, Gregory the theologian, and Gregory of Nyssa, Ambrose, Augustine, Theophilus, John of Constantinople, Cyril, Leo, Proclus; and we accept what they have set down on the correct belief and the condemnation of heretics.” But it is manifest from many testimonies of Augustine, especially his On the Trinity and his Exposition of John, that the Holy Spirit is from the Son. It must, then, be conceded that the Holy Spirit is from the Son just as He is from the Father.