Basil: Contra Eunomius 2.29

What do I claim? I say that unless the light it something different from unbegottenness, then one can no longer attribute it to the Son, just as one cannot attribute unbegottenness itself to him. The following teaches us how the meanings of the words differ. God is said to dwell in light [1Tim 6.16] and to be robed in light [Ps 103.2], but nowhere does the Word say that he dwells in his own unbegottenness or that unbegottenness surrounds him externally—for such things are ridiculous. Rather, begottenness and unbegottenness are distinctive features that enable identification. If there were nothing that characterised the substance, there would be no way for our understanding to penetrate it. Since the divinity is one, it is impossible to receive a notion of the Father or the Son that distinguishes each, unless our thinking is nuanced by the addition of the distinguishing marks.

Our response to the objection that God will be revealed as composite unless the light is understood to be the same thing as unbegotten goes as follows. If we were to understand unbegottenness as part of the substance, there would be room for the argument which claims that what is compounded from things is composite. But if we were to posit, on the one hand, the light or the life or the good as the substance of God, claiming that the very thing which God is is life as a whole, light as a whole, and good as a whole, while positing, on the other hand, that the life has unbegottenness as a concomitant, then how is the one who is simple in substance not incomposite? For surely the ways of indicating his distinctive feature will not violate the account of simplicity. Otherwise, all the things said about God will indicate to us that God is composite. And so, it seems that if we are going to preserve the notion of simplicity and partlessness, there are two options. Either we will not claim anything about God except that he is unbegotten, and we will refuse to name him ‘invisible,’ incorruptible,’ ‘immutable,’ ‘creator,’ ‘judge,’ and all the names we now use to glorify him. Or, if we do admit these names what will we make of them? Shall we apply all of them to the substance? If so, we will demonstrate not only that he is composite, but also that he is compounded from unlike parts, because different things are signified by each of these names. Or shall we take them as external to the substance? So, whatever account of attribution they dream up for each of these names, they should apply the designation ‘unbegotten’ in the same way.