Accentuation rules for final η when followed by ι (iota subscript/adscript); circumflex (περισπῶται) vs grave vs acute in dative and particles; examples and dialectal notes.
Τὰ εἰς 'η' μετὰ τοῦ 'ι', εἰ ἀπὸ δοτικῶν εἴη μηδὲ θαυμαστικά, ἢ βαρύνεται ἢ περισπᾶται, οὐδέποτε δὲ ὀξύνεται. περισπᾶται μὲν διπλῇ καὶ τριπλῇ, πεζῇ, πῇ, ὁμαρτῇ καὶ ἁμαρτῇ, κομιδῇ, διχῇ, τριχῇ, τετραχῇ, ἀλλαχῇ, μοναχῇ, ἡσυχῇ, ὁμῇ, σιωπῇ, ἐνωπῇ. βαρύνεται δὲ πάντῃ, ἄλλῃ, ταύτῃ· τοιοῦτόν ἐστι καὶ τὸ ἀμηγέπῃ παρ´ Ἀττικοῖς. τὸ ἤδη τῶν βαρυτονουμένων χωρὶς τοῦ 'ι' γράφεται καὶ τὸ νῦν δή, ὅτε σημαίνει τὸ πρὸ ὀλίγου «οὗτος ἀνὴρ νῦν δὴ ξυμβλήμενος» (ω 260), ἐστὶ σύνθετον ὡς καὶ τὸ δηλαδή ὀξυνόμενον. τὸ δὲ μή ἀπαγορευτικὸν καὶ νή καὶ ἥ ἀντὶ τοῦ ὡς καὶ φή «φὴ νέος οὐκ ἀπάλαμνος» χωρὶς τοῦ 'ι' γράφεται καὶ ὀξύνεται. καὶ τὰ καθαρεύοντα μὴ δηλοῦντα χρόνον ὀξύνεται οἷον ἰή ὠή ἰωή. ὥστε λοιπὸν εἴ τι εἰς 'η' λήγει καὶ ἐπὶ τέλει τὸν τόνον ἔχει, τοῦτο καὶ περισπᾶται καὶ τὸ 'ι' ἔχει προσγεγραμμένον. Καὶ τὸ ἰδίᾳ δὲ καὶ δημοσίᾳ ἀπὸ δοτικῆς γέγονε· καὶ τὸ κατωκάρᾳ παρ´ Ἀθηναίοις «κατωκάρᾳ ῥίψας με βουκολήσεται» (Arist. Pac. 153) ἐπίρρημά ἐστι σύνθετον καὶ σὺν τῷ 'ι' γράφεται. τὸ ἁμᾷ οἱ Δωριεῖς περισπῶσι καὶ τὸ παντᾷ ὥσπερ καὶ τὸ κρυφᾷ παρὰ Πινδάρῳ· τοιοῦτον δέ ἐστι καὶ τὸ ἁμᾷ (Pyth. III 65) ἀπὸ τοῦ ἁμῇ γινόμενον. ζητεῖται δὲ ἐν τῷ περισπωμένῳ ἁμᾷ, εἰ προστεθήσεται τὸ 'ι'.
Those ending in -η with an ι, if they are from datives and not exclamatory, are either barytone or circumflexed, but are never acute. They are circumflexed in διπλῇ and τριπλῇ, πεζῇ, πῇ, ὁμαρτῇ and ἁμαρτῇ, κομιδῇ, διχῇ, τριχῇ, τετραχῇ, ἀλλαχῇ, μοναχῇ, ἡσυχῇ, ὁμῇ, σιωπῇ, ἐνωπῇ. They are barytone in πάντῃ, ἄλλῃ, ταύτῃ; of this sort too is ἀμηγέπῃ among the Attic writers. ἤδη, among the barytone words, is written without the ι, and so is νῦν δή when it means ‘a little while ago’: “οὗτος ἀνὴρ νῦν δὴ ξυμβλήμενος” (ω 260); it is a compound, as also δηλαδή, which is acute. But the prohibitive μή, and νή, and ἥ in place of ὡς, and φή—“φὴ νέος οὐκ ἀπάλαμνος”—are written without the ι and are acute. And the pure forms not denoting time are acute, for example ἰή, ὠή, ἰωή. Therefore, if anything ends in -η and has the accent on the final syllable, it is also circumflexed and has the ι written as an iota subscript. And ἰδίᾳ and δημοσίᾳ too have arisen from the dative; and κατωκάρᾳ among the Athenians—“κατωκάρᾳ ῥίψας με βουκολήσεται” (Arist. Pac. 153)—is a compound adverb and is written with the ι. The Dorians circumflex ἁμᾷ and also παντᾷ, just as also κρυφᾷ in Pindar; and of this sort too is ἁμᾷ (Pyth. III 65), formed from ἁμῇ. But in the circumflexed ἁμᾷ it is asked whether the ι will be added.