After reading through St. Augustine’s De Trinitate, I’ve made it a commitment to finally write out a thorough article on this great Saint, venerated universally by East and West, and his theology of the Spirit’s eternal procession. However, since such a work requires much thought, re-reading, and re-packaging of immense thoughts and arguments into smaller ones, I’ve been continuously delayed from being able to publish this sooner than later. Lord willing, this will be out shortly. Another 2 weeks, I suspect. In any case, I did take the time to identify all the important passages where Augustine speaks to the matter of the Spirit’s procession from both the Father and the Son, along with attending argumentation and detail from Augustine himself. This way you can be familiar with some of his thought before I get deeper into the theology and his argument overall. One point I will make here is this – It is unmistakable that Augustine held to an eternal procession (Ad Intra) or spiration of the Holy Spirit from both the Father and the Son as from one single principle, as the Ecumenical Council of Florence made explicit, as well as the modern universal Catholic Catechism. There are some few persons who try to think that what Augustine says here is entirely within the construction of an “eternal manifestation” of the Spirit through the Son (cf. Gregory of Cyprus II and Gregory Palamas), or that he speaks merely of an external procession of the Spirit from the Son, more popularly referred to as the “economic procession” (Ad Extra). I can’t go into the reasons why this is simply wrong, but I can foretell that you will not be able to get this latter sense even in the below citations. But, for the sake of thoroughness, I promise to release the more in-depth article as soon as I can. And lastly, you may want to keep this reference in your own archives since I’ve not found any articles or websites online which provide such an extensive Florilegium from Augustine’s book on the Trinity in support of the Filioque doctrine. Enjoy!
“As, therefore, the Father begot, the Son is begotten; so the Father sent, the Son was sent. But in like manner as He who begot and He who was begotten, so both He who sent and He who was sent, are one, since the Father and the Son are one. So also the Holy Spirit is one with them, since these three are one. For as to be born, in respect to the Son, means to be from the Father; so to be sent, in respect to the Son, means to be known to be from the Father. And as to be the gift of God in respect to the Holy Spirit, means to proceed from the Father; so to be sent, is to be known to proceed from the Father. Neither can we say that the Holy Spirit does not also proceed from the Son, for the same Spirit is not without reason said to be the Spirit both of the Father and of the Son. Nor do I see what else He intended to signify, when He breathed on the face of the disciples, and said, ‘Receive the Holy Ghost‘. For that bodily breathing, proceeding from the body with the feeling of bodily touching, was not the substance of the Holy Spirit, but a declaration by a fitting sign, that the Holy Spirit proceeds not only from the Father, but also from the Son. For the veriest of madmen would not say, that it was one Spirit which He gave when He breathed on them, and another which He sent after His ascension. For the Spirit of God is one, the Spirit of the Father and of the Son, the Holy Spirit, who works all in all. But that He was given twice was certainly a significant economy, which we will discuss in its place, as far as the Lord may grant. That then which the Lord says —Whom I will send unto you from the Father, — shows the Spirit to be both of the Father and of the Son; because, also, when He had said, Whom the Father will send, He added also, in my name. Yet He did not say, Whom the Father will send from me, as He said, Whom I will send unto you from the Father,— showing, namely, that the Father is the beginning (principium) of the whole divinity, or if it is better so expressed, deity. He, therefore, who proceeds from the Father and from the Son, is referred back to Him from whom the Son was born (natus).” (De Trinitate Book IV, Ch. 20)
“Therefore, since the Father, the Son and the Holy Spirit are one God, and certainly God is holy, and God is a spirit, the Trinity can be called also the Holy Spirit. But yet that Holy Spirit, who is not the Trinity, but is understood as in the Trinity, is spoken of in His proper name of the Holy Spirit relatively [i.e. by relation], since He is referred both to the Father and to the Son, because the Holy Spirit is the Spirit both of the Father and of the Son. But the relation is not itself apparent in that name, but it is apparent when He is called the gift of God; for He is the gift of the Father and of the Son, because ‘He proceeds from the Father’, as the Lord says; and because that which the apostle says, ‘Now, if any man have not the Spirit of Christ, he is none of His’, he says certainly of the Holy Spirit Himself. When we say, therefore, the gift of the giver, and the giver of the gift, we speak in both cases relatively in reciprocal reference. Therefore the Holy Spirit is a certain unutterable communion of the Father and the Son; and on that account, perhaps, He is so called, because the same name is suitable to both the Father and the Son. For He Himself is called specially that which they are called in common; because both the Father is a spirit and the Son a spirit, both the Father is holy and the Son holy. In order, therefore, that the communion of both may be signified from a name which is suitable to both, the Holy Spirit is called the gift of both. And this Trinity is one God, alone, good, great, eternal, omnipotent; itself its own unity, deity, greatness, goodness, eternity, omnipotence.” (De Trinitate, Book V, Ch. 11)
“And so when we say, both that the Father is the Beginning, and that the Son is the Beginning, we do not speak of two beginnings of the creature [i.e. creation in general]; since both the Father and the Son together is one beginning in respect to the creature, as one Creator, as one God. But if whatever remains within itself and produces or works anything is a beginning to that thing which it produces or works; then we cannot deny that the Holy Spirit also is rightly called the Beginning, since we do not separate Him from the appellation of Creator: and it is written of Him that He works; and assuredly, in working, He remains within Himself….But in their mutual relation to one another in the Trinity itself, if the begetter is a beginning in relation to that which he begets, the Father is a beginning in relation to the Son, because He begets Him; but whether the Father is also a beginning in relation to the Holy Spirit, since it is said,
He proceeds from the Father, is no small question. Because, if it is so, He will not only be a beginning to that thing which He begets or makes, but also to that which He gives….If, therefore, that also which is given has him for a beginning by whom it is given, since it has received from no other source that which proceeds from him; it must be admitted that the Father and the Son are a Beginning (principium, Eng. Principle) of the Holy Spirit, not two Beginnings (principia); but as the Father and Son are one God, and one Creator, and one Lord relatively to the creature, so are they one Beginning relatively to the Holy Spirit. But the Father, the Son, and the Holy Spirit is one Beginning in respect to the creature, as also one Creator and one God.” (De Trinitate Book V, Ch. 13-14)
“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. And Itself is that very power that went out from Him, as we read in the Gospel, and healed them all…..Are we therefore able to ask whether the Holy Spirit had already proceeded from the Father when the Son was born, or had not yet proceeded; and when He was born, proceeded from both, wherein there is no such thing as distinct times: just as we have been able to ask, in a case where we do find times, that the will proceeds from the human mind first, in order that that may be sought which, when found, may be called offspring; which offspring being already brought forth or born, that will is made perfect, resting in this end, so that what had been its desire when seeking, is its love when enjoying; which love now proceeds from both, i.e. from the mind that begets, and from the notion that is begotten, as if from parent and offspring? These things it is absolutely impossible to ask in this case, where nothing is begun in time, so as to be perfected in a time following. 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? For while we do not say that the Holy Spirit is begotten, yet we do not therefore dare to say that He is unbegotten, lest any one suspect in this word either two Fathers in that Trinity, or two who are not from another. For the Father alone is not from another, and therefore He alone is called unbegotten, not indeed in the Scriptures, but in the usage of disputants, who employ such language as they can on so great a subject. And the Son is born of the Father; and the Holy Spirit proceeds from the Father principally, the Father giving the procession without any interval of time, yet in common from both [Father and Son]. But He would be called the Son of the Father and of the Son, if — a thing abhorrent to the feeling of all sound minds — both had begotten Him. Therefore the Spirit of both is not begotten of both, but proceeds from both. (De Trinitate, Book 15, Ch. 26)
“But because it is most difficult to distinguish generation from procession in that co-eternal, and equal, and incorporeal, and ineffably unchangeable and indivisible Trinity, let it suffice meanwhile to put before those who are not able to be drawn on further, what we said upon this subject in a sermon to be delivered in the ears of Christian people, and after saying wrote it down. For when, among other things, I had taught them by testimonies of the Holy Scriptures that the Holy Spirit proceeds from both, I continue: If, then, the Holy Spirit proceeds both from the Father and from the Son, why did the Son say, ‘He proceeds from the Father.’ Why, think you, except as He is wont to refer to Him, that also which is His own, from whom also He Himself is? Whence also is that which He says, ‘My doctrine is not my own, but His that sent me?’ If, therefore, it is His doctrine that is here understood, which yet He said was not His own, but His that sent Him, how much more is it there to be understood that the Holy Spirit proceeds also from Himself, where He so says, He proceeds from the Father, as not to say, He proceeds not from me? From Him, certainly, from whom the Son had his Divine nature, for He is God of God, He has also, that from Him too proceeds the Holy Spirit; and hence the Holy Spirit has from the Father Himself, that He should proceed from the Son also, as He proceeds from the Father. Here, too, in some way may this also be understood, so far as it can be understood by such as we are, why the Holy Spirit is not said to be born, but rather to proceed; since if He, too, was called a Son, He would certainly be called the Son of both, which is most absurd, since no one is son of two, save of father and mother. But far be it from us to surmise any such thing as this between God the Father and God the Son. Because not even the son of men proceeds at the same time from both father and mother; but when he proceeds from the father into the mother, he does not at that time proceed from the mother; and when he proceeds from the mother into this present light, he does not at that time proceed from the father. But the Holy Spirit does not proceed from the Father into the Son, and from the Son proceed to sanctify the creature, but proceeds at once from both; although the Father has given this to the Son, that He should proceed, as from Himself, so also from Him. For we cannot say that the Holy Spirit is not life, while the Father is life, and the Son is life: and hence as the Father, while He has life in Himself, has given also to the Son to have life in Himself; so has He given also to Him that life should proceed from Him, as it also proceeds from Himself. I have transferred this from that sermon into this book, but I was speaking to believers, not to unbelievers…. Lift up your eyes to the light itself, and fix them upon it if you can. For so you will see how the birth of the Word of God differs from the procession of the Gift of God, on account of which the only-begotten Son did not say that the Holy Spirit is begotten of the Father, otherwise He would be His brother, but that He proceeds from Him. Whence, since the Spirit of both is a kind of consubstantial communion of Father and Son” (De Trinitate, Book 15, Ch. 27)