Discussion of perispast accentuation: the vocative ὦ and related forms, contemptuous ὢ, addition of 'ι' producing ᾥτε/ᾥπερ through loss of s and vowel coalescence, formation of prōî/prōn accents, behavior of words with οι/ει/υ diphthongs, examples from Aristophanes, and exceptions among adverbial forms (αὐτοῦ, τηλοῦ, ἀγχοῦ, πανταχοῦ, ἀλλαχοῦ, ὁμοῦ). Note of ἰδού ἰού and οὐ negative.
Καὶ τὸ ὦ κλητικὸν περισπᾶται «ὦ ἄνθρωπε». ὅτε δὲ σχετλιαστικόν, ὀξύνεται «ὢ τί ς´ εἴπω» (Ar. Nub. 1378) καὶ ὅτε προσγράφεται αὐτῷ τὸ 'ι' καὶ ταὐτὸν σημαίνει τῷ ὥσπερ «ἀλλ´ ἔχον ᾥτε τάλαντα γυνὴ χερνῆτις ἀληθής» (Μ 433) καὶ ᾥπερ· γίνεται δὲ οὕτως· ὡσείτε καὶ ὡσείπερ καὶ ἀποβολῇ τοῦ 'σ' καὶ κράσει τοῦ 'ω' καὶ 'ε' εἰς τὴν 'ῳ' δίφθογγον διὰ τὴν τοῦ 'ι' συναίρεσιν ᾥτε καὶ ᾥπερ. Τὸ μέντοι πρῴ μονοσύλλαβον παρ´ Ἀττικοῖς ὀξύνεται, ἐπεὶ ἐκ τοῦ πρωΐ δισυλλάβου ὀξυνομένου κατὰ συναίρεσιν γέγονε. τὸ δὲ πρῷν περισπᾶται «οὐ πρῷν μὲν ἡμῖν ὁ τραγῳδὸς ἤγειρεν» (Callim. chol. fr. 18 Mein.), ἐπεὶ ἐκ τοῦ πρῶϊν. Τὰ ἔχοντα τὴν 'οι' δίφθογγον ἢ τὴν 'ει' περισπᾶται. Ἀριστοφάνης ἐν Βατράχοις ( 199) «ἵζω ´πὶ κώπην, οἷπερ ἐκέλευσάς με σύ». ποῖ, εἷ «εἷ τὰ τῶν χοιραγχᾶν». Σώφρων. «πεῖ γὰρ ἁ ἄσφαλτος». κεῖ παρὰ Ἀρχιλόχῳ. ὅτε δὲ ἐπίρρημά ἐστιν εὐκτικόν, τὸ εἴ ὀξύνεται ὁμοίως τῷ συνδέσμῳ «εἴγ´ ὤφελες». τὸ γὰρ στοιχεῖον περισπᾶται. καὶ τὸ φνεί παρ´ Ἀριστοφάνει· ἔστι δὲ μίμημα φωνῆς ὀρνέου. καὶ πάντα ὅσα εἰς τὴν διὰ τοῦ 'υ' δίφθογγον περισπᾶται, εὖ, φεῦ, ποῦ, οὗ τὸ δασυνόμενον. κἂν ὑπὲρ μίαν συλλαβὴν εἴη, ὁμοίως περισπᾶται πλὴν τῶν ἀναφορικῶν, αὐτοῦ, τηλοῦ, ἀγχοῦ, πανταχοῦ, ἀλλαχοῦ, ὁμοῦ καὶ τὰ λοιπὰ πάντα. σημειωτέον ἰδού ἰού καὶ οὐ ἀρνητικόν. ταῦτα γὰρ
And the vocative ὦ is circumflexed: «ὦ ἄνθρωπε». But when it is exclamatory, it is accented with an acute: «ὢ τί ς´ εἴπω» (Ar. Nub. 1378); and when the 'ι' is written with it and it has the same meaning as ὥσπερ, as in «ἀλλ´ ἔχον ᾥτε τάλαντα γυνὴ χερνῆτις ἀληθής» (Μ 433), and likewise ᾥπερ. It comes about as follows: ὡσείτε and ὡσείπερ, and by dropping the 'σ' and by contraction of 'ω' and 'ε' into the diphthong 'ῳ' because of the synaeresis of 'ι', ᾥτε and ᾥπερ.
The monosyllabic πρῴ, however, among the Attic writers is accented with an acute, since it has come by synaeresis from the disyllabic πρωΐ, which is accented with an acute. But πρῷν is circumflexed: «οὐ πρῷν μὲν ἡμῖν ὁ τραγῳδὸς ἤγειρεν» (Callim. chol. fr. 18 Mein.), since it is from πρῶϊν.
Words that have the diphthong 'οι' or 'ει' are circumflexed. Aristophanes in Frogs (199): «ἵζω ´πὶ κώπην, οἷπερ ἐκέλευσάς με σύ». ποῖ, εἷ: «εἷ τὰ τῶν χοιραγχᾶν». Sophron: «πεῖ γὰρ ἁ ἄσφαλτος». κεῖ in Archilochus.
But when it is an optative adverb, εἴ is accented with an acute, like the conjunction: «εἴγ´ ὤφελες»; for the letter is circumflexed. And φνεῖ in Aristophanes; it is an imitation of the voice of a bird.
And all words that end in the diphthong written with 'υ' are circumflexed: εὖ, φεῦ, ποῦ, οὗ, the last being aspirated. And even if it is more than one syllable, it is likewise circumflexed, except the relative forms: αὐτοῦ, τηλοῦ, ἀγχοῦ, πανταχοῦ, ἀλλαχοῦ, ὁμοῦ, and all the rest. It should be noted: ἰδού, ἰού, and οὐ as a negative. For these…