Why is this query posted in the subcategory "Vocabulary"? It's not a question about vocabulary but rather about grammatical usage. You're not asking about the meaning of the word θεὸς in John 1:1c but rather about how it is used in this particular instance, and you're asking about it as if it were a matter of standard usage such as might readily be raised in a first-year grammar book. "Qualitative verses
adjectival"? I suppose that you mean "qualitative versus
adjectival." But "qualitative" and "adjectival" are hardly antithetical. Ordinarily adjectives are qualitative. Now the question is whether a Predicate nominative is or can be adjectival -- but, of course it can: there's hardly a more standard ordinary formulation than something like "ἕρυθρόν ἐστι τὸ πρόσωπον τοῦ φίλου ἡμῶν." But you seem to mean to ask whether a predicate noun
can be qualitative, and you ask this as if it were a generalizing query when in fact you want to know about a specific instance: θεὸν in John 1:1c. It's pretty clear that you're raising a theological question here about a specific verse. We don't deal with theological questions or theological implications here but with questions that can be dealt with in terms of what we know of how the Biblical Greek language works. The questions you're raising have been discussed over and over in the old B-Greek list that pre-dated this Forum. Access a search box at: https://www.google.com/cse?cx=012625948 ... #gsc.tab=0
and type in "John 1:1c" or "QEOS" or "QEOS HN hO LOGOS" -- you'll find page after page of references to earlier discussions of this passage from the old B-Greek archives. There were several discussions of it in 2006.
For now I'm going to declare this topic closed and lock the discussion.