I’m not convinced Gregory’s argument from opposites ( Against Eunimius 9.4) is sound, but it’s intriguing and engaging.

Here’s the argument: Certain realities have direct opposites that cannot coexist.  Light cannot coexist with darkness, but expels and destroys it.  On the other hand, darkness can expel light.  So also with the oppositions of good/bad, falsehood/truth.  No middle terms exist here, but simple polarities.  So, in the creation account, before God calls light into being, there is only darkness.  Now, the Son is Light; and if the Son once was not, then what was could not be some neutral neither-light-nor-darkness, nor some middle light-darkness.  Before the Father generated the Son, there must have been darkness.

It “necessarily” follows that prior to the begetting of the Son, Eunomius’s god was enveloped in darkness: “surrounded by darkness instead of Light, by falsehood instead of truth, by death instead of life, by evil instead of good.”  If “ungenerate light” is one thing, and “generate light” is another, then it follows that “it is impossible that the light [that is, the generated light] should shine forth save out of darkness.”  Between the ungenerate and ungenerating light of the Father and the generated light of the Son is an “interval of darkness,” a cloud of unbeing from which or through which the Ungenerate Father has to cut in order to generate a Son.

One of the many interesting implications of this is that Arianism falls back into the ontology of violence characteristic of combat myths.  To begin to be productive, the ungenerate must contend with his opposite.  To generate or shine the light that Eunomius claims he is, he must first overcome darkness.  The god of Eunomius may be able to forge some kind of demiurge; he is incapable of creating in the way that Genesis says Yahweh creates.