OK, to show my good will, let me be the kind soul in question.
επ-εμ-πίπτει, like εμ-πίπτει, would take a dative (εμπιπτει “falls on,” επεμ- combining “against” with “on”, making it hostile, an attack). The construction remains the same when an internal accusative is added to the verb, as here (τηνδε βασιν).
So we’re back once more to internal accusatives. If the verb επεμπιπτει took a direct object, that would be an external accusative. The verb happens to take dative (because of the εν- prefix), but that’s the only difference. τηνδε επεμπιπτει βασιν “he launches this attack” (let’s say; lit. “he this-step-attacks”), ποιμνιαις “on the flocks.”
It’s like e.g. αυτους τηνδε την παιδείαν ἐπαίδευσεν (“he gave them this education,” “he educated them in this way”), except that here the verb takes dative (ποιμναις) not accusative (αυτους). And of course τηνδε την παιδειαν επαιδευσεν is a much more prosaic expression than τηνδε βασιν επεμπιπτει, which strikes me as typically Sophoclean.
So your first question does not really admit of a good answer in the either/or form in which you ask it. But to answer in terms of what “modifies” what: τηνδε βασιν modifies επεμπιπτει, while ποιμναις modifies the whole expression τηνδ’ επεμπιπτει βασιν.
Any clearer?
Your second query is irrelevant to this verse and it’s unclear what you mean by “a common noun like βάσιν.” You do very occasionally find datives modifying nouns, but not normally. Datives without prepositions should be referred to verbs or verbal expressions, as here. In your lingo that would make them adverbial, though a noun cannot be an adverb, a different part of speech, and I wouldn’t say it can “function” as one either (except in fixed usages such as τέλος "finally).
As to your edit, nouns function as nouns, not as adjectives. στρατηγίς is the sort of formation that could be either an adjective or a noun. Here it’s an adjective, as it almost always is. It’s dative only because πυλαις is dative; the case is immaterial.
δισσαις στρατηγισιν πυλαις is a portmanteau kind of expression. We are to think of two commanders, not two gates. Strict word-by-word grammatical analysis is not always up the job of explaining poetic expressions.
Hope this helps.
Edit. This crossed with your follow-up post, which I’ve just seen. I wouldn’t have thought you ought to feel you should withdraw entirely. It’s true that when seneca in his original post said he wanted to go slowly and carefully he might not have meant quite this slowly and carefully, but your questions are far from “impertinent” and may help others here reach a clearer understanding of tricky things that might otherwise escape attention.
I’ll leave it to seneca to say what he thinks, but for myself, I don’t see why you shouldn’t continue here. Textkit is as much for you as it is for anyone else, and unless and until moderators step in, you’re free to post whatever you like, just as seneca is, just as I am. But as I already suggested above, I think it might be as well “if you limited yourself to a few things that you find especially problematic, and took fewer pains to explain yourself.”
Michael
