What Did the Homoians Believe About the Trinity

And how did Augustine respond to their Latin Homoian (Arian) arguments

Latin Arians (using Eunomian-esque arguments) claimed that the names Father and Son revealed their nature (words → nature). Father means unbegotten and Son means begotten, both of which are two different but similar natures. Hence, Father and Son are God, but one is True God and the other merely God—God from True God.

Augustine replied to this Homoian argument by citing Jesus: “I and the Father are one” (John 10:30). So if all predication is substantial (ad se), what sort of thing is being said here and in other like places?

Here, Jesus affirms the oneness of essence, Augustine argues. In this and other texts, the Father and Son are seen as one in nature. So how can, as the Arians believe, the Father and Son be two—as Father and Son—and yet one, as passages like John 10:30 say?

Augustine points out that Scripture has an idiom that speaks of the Father and Son as one, and also as two. This is because words do not always provide direct, immediate access to divine nature. One must “save the appearance,” as the medievals might later say.

According to Augustine, Scripture sometimes presents the Father and Son as speaking of essence (ad se), and at other times, as speaking in terms of relation (ad aliquid). The name Father reveals that he is Father to the Son, and the name Son reveals that he is Son to the Father. While both are the one Being that God is, their names do not reveal a diversity of natures but rather a distinction of relation: Father–Son, Not begotten–Begotten, God–Word, etc.

Augustine’s major point is this: the Latin Arians (Homoians) lacked a sufficient epistemology—a theory of signs. They misunderstood how words signify meaning. They assumed that names bluntly revealed essences, when in fact many names in Scripture predicate relation, not substance, especially terms like Father and Son.

Texts like John 10:30 press back against Arian readings. One must explain how the Father and Son are one, yet also distinguishable. How and in what way?

For Augustine, the answer is simple: one in essentia, two by relations of origin. Of course, Augustine includes the Holy Spirit in his larger Trinitarian logic. But here I am summarizing the main thrust of his argument in Book V of On the Trinity.