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1 Consider also this: if the Spirit’s being supplied by the Son is not different from his proceeding from the Father, one of two things must follow: either the Son too is a cause of the Spirit, or the Father is merely one who supplies him, as the Son is. If the Son is the cause of the Spirit, there are two principles of the one. And what needs more than one principle for its existence will be either greater than what has its being from a single principle, or equal, or less; but it cannot be equal, for then it would be from one—so it must be either greater or less. The Spirit, then, will be either greater than the Son (and see the innovation of this impiety! none of those who ever dared speak against the Son ventured to say this), or he will be less, and Macedonius[1] lives again.
2 But if he is merely supplied by the Father, as he is by the Son, then either he will be without a principle himself—and where, then, is the Father’s dignity, and how has his property become common? — or we will have to look for some other cause of him, and a quaternity of persons will be introduced to us, and a duality of godheads: one belonging to the three, the other to the fourth, newly brought in, who proceeds to us out of your astonishing innovation. Further, if to proceed is the same as to be supplied, I ask: what other word signifies the manner in which the Spirit is from the Father? Further still: if the Father is greater than the Son by reason of being his cause, he will be greater than the Spirit for the same reason; but if the Son too is a cause of the Spirit, he too will in the same way be greater than him. And where have you found this—that the Son is said to be greater than the Spirit?
3 Further: if the Lord’s breathing on the disciples signifies, on your view, the Spirit’s procession from him—which would be the giving of the whole, clearly, and not of a single gift—then he gave them the Comforter at that moment. Where, then, is the saying, If I do not go away, he will not come to you? Again: if the Comforter himself was given then, through the breathing, and not merely the gift of the remission of sins (for Scripture knows how to call the gifts also “spirits”), then his coming at Pentecost was either of the same Spirit, and so superfluous, or of another Spirit—and we would then have to ask which. These, then, are the arguments we bring to establish that the Spirit proceeds from the Father alone, and not also from the Son.