Accentuation rules for Greek plural nouns: neuter plurals in -α (genitive) showing alternations with oxytone, perispomenon, barytone; dative plurals in -αις/-οις; Attic tone patterns; accusative plural accent behavior.
Αἱ εἰς 'α' λήγουσαι εὐθεῖαι πληθυντικαὶ οὐδετέρων ὀνομάτων, εἰ μὲν ὀξύνοιντο ἢ περισπῷντο, πάντως τὴν πληθυντικὴν γενικὴν περισπῶσι, πυρά πυρῶν, σφυρά σφυρῶν, καλά καλῶν, ἀλλὰ καὶ κανᾶ περισπωμένως κανῶν, ὀστᾶ ὀστῶν, χρυσᾶ χρυσῶν· εἰ μέντοι βαρύνοιντο, συμβαρύνουσι καὶ τὰς γενικάς, φίλα φίλων, ξύλα ξύλων, φῶτα φώτων, ὦτα ὤτων. εἰ δὲ ἀπὸ περισσοσυλλάβων συναλοιφὴ παρακολουθήσειε, ἡ γενικὴ πάντως περισπᾶται, τειχέων τειχῶν, βελέων βελῶν, κρεάων κρεῶν. σεσημείωται τὸ φρητῶν. ἔστι γὰρ φρέατα καὶ γίνεται κατὰ κρᾶσιν φρῆτα τοῦ 'ε' καὶ 'α' εἰς 'η' κραθέντος. καὶ τούτου βαρυνομένου κατὰ τὴν εὐθεῖαν τῶν πληθυντικῶν ὤφειλε καὶ ἡ γενικὴ τῶν πληθυντικῶν βαρύνεσθαι καὶ εἶναι φρήτων βαρυτόνως ὥσπερ τὰ ὦτα τῶν ὤτων, τὰ φῶτα τῶν φώτων. ὅμως δὲ περισπῶσιν αὐτὸ οἷον φρητῶν ὁμοτόνως τῇ Κρητῶν καὶ σητῶν καὶ θητῶν γενικῇ. {1Περὶ τόνου τῆς δοτικῆς πληθυντικῆς.}1 Περὶ μὲν τῶν εἰς 'ι' ἐκφωνούμενον δοτικῶν πληθυντικῶν εἴπομεν ἐν τοῖς ἑνικοῖς, νῦν δὲ περὶ τῶν λοιπῶν ἐροῦμεν. Αἱ εἰς 'αις' καὶ εἰς 'οις' ἀπὸ ὀξυτόνων καὶ περισπωμένων εὐθειῶν οὖσαι περισπῶνται, ἀθληταί ἀθληταῖς, καλοί καλοῖς, σοφοί σοφοῖς, ἀλλὰ καὶ οἱ Ἑρμαῖ τοῖς Ἑρμαῖς, αἱ χρυσαῖ ταῖς χρυσαῖς. ἀπὸ δὲ βαρυτόνων πρὸ μιᾶς ἔχουσι τὸν τόνον, φίλοι φίλοις, ἵπποι ἵπποις, Μήδειαι Μηδείαις, τάλαιναι ταλαίναις, ξύλα ξύλοις. Περὶ τῶν Ἀττικῶν, ὅτι τὸν τόνον τῆς κοινῆς εὐθείας ἔχει πᾶσα πτῶσις Ἀττική, εἴπομεν ἤδη· διὰ τοῦτο τοῖς Μενέλεῳς προπαροξύνομεν, ἐπεὶ καὶ ὁ Μενέλαος, τοῖς δὲ λεῴς ὀξύνομεν, ἐπεὶ καὶ ὁ λαός. {1Περὶ τόνου τῆς πληθυντικῆς αἰτιατικῆς.}1 Πᾶσα αἰτιατικὴ πληθυντικὴ ὁμοφωνοῦσα τῇ πληθυντικῇ εὐθείᾳ καὶ ὁμοτονεῖ ταύτῃ, οἱ ταχεῖς τοὺς ταχεῖς, οἱ Δημοσθένεις τοὺς Δημοσθένεις,
Nominative plurals of neuter nouns ending in -α, if they are accented with an acute or a circumflex, in every case circumflex the genitive plural: πυρά πυρῶν, σφυρά σφυρῶν, καλά καλῶν, and also κανᾶ with a circumflex, κανῶν, ὀστᾶ ὀστῶν, χρυσᾶ χρυσῶν. But if they are accented with a grave, they accent the genitives with a grave as well: φίλα φίλων, ξύλα ξύλων, φῶτα φώτων, ὦτα ὤτων. And if contraction should follow from polysyllables, the genitive is in every case circumflexed: τειχέων τειχῶν, βελέων βελῶν, κρεάων κρεῶν. Noted as exceptional is φρητῶν. For there is φρέατα, and by crasis it becomes φρῆτα, the ε and α having been blended into η. And since this is accented with a grave in the nominative plural, the genitive plural too ought to be accented with a grave and be φρήτων with a grave accent, just as τὰ ὦτα has τῶν ὤτων, τὰ φῶτα has τῶν φώτων. Nevertheless they circumflex it, as φρητῶν, with the same accent as the genitive Κρητῶν and σητῶν and θητῶν.
{1On the accent of the dative plural.}1 Concerning dative plurals pronounced with -ι we spoke in the discussion of the singulars; now we shall speak about the rest. Those in -αις and in -οις, when they come from nominatives accented with an acute or a circumflex, are circumflexed: ἀθληταί ἀθληταῖς, καλοί καλοῖς, σοφοί σοφοῖς, and also οἱ Ἑρμαῖ τοῖς Ἑρμαῖς, αἱ χρυσαῖ ταῖς χρυσαῖς. But those from barytone nominatives have the accent on the syllable before the last: φίλοι φίλοις, ἵπποι ἵπποις, Μήδειαι Μηδείαις, τάλαιναι ταλαίναις, ξύλα ξύλοις. Concerning the Attic forms, that every Attic case has the accent of the common nominative, we have already spoken; for this reason we accent τοῖς Μενελέῳς with a proparoxytone, since also ὁ Μενέλαος, but we accent τοῖς λεῴς with an acute, since also ὁ λαός.
{1On the accent of the plural accusative.}1 Every plural accusative that is identical in sound with the plural nominative also has the same accent as it: οἱ ταχεῖς τοὺς ταχεῖς, οἱ Δημοσθένεις τοὺς Δημοσθένεις,