accusative being used to express an origin?

Question

I read in Plutarch (Demosthenes.1) the phrase

ὑπάρξαι ‘τὰν πόλιν εὐδόκιμον‘ (~ to be born in ‘a famous city’).

(τὰν πόλιν εὐδόκιμον being a quote from (pseudo-?)Euripides' ode to Alcibiades, cf Lyra Graeca, iii , p. 240-241). See the note infra for more details. The three words given by Plutarch are the only one attested : as far as I know, we don't know what Euripides wrote before these three words.

I can't figure out the construction of "ὑπάρξαι τὰν πόλιν εὐδόκιμον" This quote means something like "to be born in ‘a famous city’", according to various translations. But why the accusative ?

ὑπάρχω means "to begin, to be at the origin of" and is mainly followed by the genitive, the Greek case expressing the origin. As far as I know, the accusative is only used after ὑπάρχω if the meaning is "to take the initiative in". In Plutarch's sentence, the meaning must be something like "to be from ~" and a genitive was expected.

The fact that Plutarch quotes a poem (moreover, written in another Greek dialect!) increases the level of difficulty.

Is the construction ὑπάρχω + acc. with the meaning "to be (born) from ~" natural ? Are there other examples in Greek litterature ?

More generally speaking, is there a linguistic way to explain how the accusative case can express an origin ? Are there other examples in Indo-European languages ?

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Plutarch, Demosthenes, 1 :

ὁ μὲν γράψας τὸ ἐπὶ τῇ νίκῃ τῆς Ὀλυμπίασιν ἱπποδρομίας
εἰς Ἀλκιβιάδην ἐγκώμιον, εἴτ᾽ Εὐριπίδης, ὡς ὁ πολὺς κρατεῖ
λόγος, εἴθ᾽ ἕτερός τις ἦν, Σόσσιε, φησὶ χρῆναι τῷ εὐδαίμονι
πρῶτον ὑπάρξαι ‘τὰν πόλιν εὐδόκιμον’ .

(Bernardotte Perrin, 1919) :

the author of the encomium upon Alcibiades for his victory in the 
chariot-race at Olympia whether he was Euripides, as the prevailing
report has it, or some other, says, Sosius that the first requisite
to a man's happiness is birth in ‘a famous city’;

Answer 1

After χρῆναι you have an accusative and infinitive construction: "it is necessary for X (acc.) to Verb (inf.)". In this case, the subject of the accusative and infinitive is τὰν πόλιν, and the predicate is εὐδόκιμον ὑπάρξαι τῷ εὐδαίμονι "to be available / be in existence (as) famous for the happy man". (τὰν πόλιν εὐδόκιμον is not actually a syntactic unit meaning "the famous city" -- that would be τὰν εὐδόκιμον πόλιν.) ὑπάρχω here is not being used in the sense "begin" but in an expanded sense, very common in Attic prose, in which it gets used as more or less as fancy synonym for εἶναι, often with the added implication that the subject is thought of as some kind of resource -- hence my translation "be available".

So a very literal translation might be "he says it is necessary that, first, the city [of his birth] should be famous for the happy man" -- more loosely, "that a happy man should have a famous city [as his birthplace]".

Answer 2

τὰν πόλιν εὐδόκιμον is accusative because it is the subject of the infinitive ὑπάρξαι, “for the famous city to be at (his) beginning”.