That’s an intriguing point, maxsims!
Let’s look more closely at my original sentence in complete form: “From the language standpoint, of course, the situation then and now are largely the same.”
By virtue of proximity, it would seem that “then and now” as a compound term is modifying the noun situation, in which case that term is functioning as an adjective phrase. If this is the case, however, then there could only be one situation for both “then” and “now,” which is a semantic absurdity. Indeed, even if the situation then and the situation now are largely the same, they remain separate and distinct entities (at least this was my intent when I wrote that sentence).
This is why it seems to me more grammatically and semantically logical to think of “then” and “now” as adverbs modifying the adjective phrase “largely the same,” even if structurally, “then and now” is closer to the noun “situation”—giving the impression that “then and now” is, in fact, an adjective phrase.
We can test either hypothesis by rewriting the sentence this way: ““From the language standpoint, of course, the situation is largely the same then and now.” The meaning is precisely the same, but here, it’s clear that “then and now” is an adverb phrase modifying the adjective phrase “largely the same.” This time, though, the noun “situation” becomes decidedly singular, requiring the singular verb-form “is.” Semantically, the focus is now primarily on “situation” as a singular concept, with everything that follows it in the sentence simply describing its particulars.
I think what this proves is that in the matter of modifying phrases, the English language actually gives wide latitude to the writer as to where to position them best in the sentence—whether for meaning, for stylistic effect, or simply for clarity's sake. Of course, this flexibility gives rise to varying interpretations as to what function a modifying phrase is performing in a sentence: as an adjective, as an adverb, as a noun, perhaps even as a conjunction. Indeed, depending on how they are used and positioned in a sentence, “now” can function as any of the four, and “then” likewise except as a conjunction. Ultimately, how they are perceived to be working in the sentence would depend on the eye and sensibility of the beholder.