Greek phonological rules describing psilosis (smooth breathing) and dasys (rough breathing) for vowels and diphthongs ('ει','ευ','οι','ου'), with examples and the roughening of initial rho; mentions exceptions and dialectal forms.
αὔω ἐπὶ τοῦ φωνεῖν ψιλοῦται, ὅταν δὲ ἐπὶ τοῦ ξηραίνειν ἢ ἅπτειν τάσσηται, τότε δασυντέον ἐστί. Ἡ 'ει' δίφθογγος ψιλοῦται οἷον εἶδος, εἰκάζω, εἴρων καὶ τὰ λοιπὰ πλὴν τοῦ εἱρκτή, Εἵλως ὁ δοῦλος καὶ εἱκώς ὁ πέμψας, καὶ εἱλίζω τὸ συστρέφω, καὶ εἱλόμην καὶ εἷμα τὸ ἱμάτιον, καὶ εἱμένος ὁ ἐνδεδυμένος καὶ εἷνα τὸ ἕνα καὶ εἵποντο ἀντὶ τοῦ ἠκολούθουν καὶ εἷσεν ἀντὶ τοῦ ἐκάθισεν, εἱστήκει καὶ εἵως ἀντὶ τοῦ ἕως καὶ εἵατο καὶ εἵλη ἡ θερμασία καὶ εἱαμενή ἀπὸ τῆς ἕσεως τῶν ὑδάτων. σεσημείωται καὶ τὸ εἷς ἀριθμητικόν. Ἡ 'ευ' δίφθογγος ψιλοῦται, οἷον εὐλή εὐλαί οἱ σκώληκες, εὐδία, εὐθεῖα, εὐνή, εὐχή, εὖρος, εὔκηλος καὶ τὰ λοιπὰ πλὴν τοῦ εὕδω τὸ καθεύδω καὶ εὕω τὸ φλογίζω καὶ εὕρω, ἀφ´ οὗ καὶ εὑρίσκω. καὶ εὗ ἀντὶ τοῦ ἑαυτοῦ κατὰ κρᾶσιν τοῦ 'ε' καὶ 'ο' εἰς τὴν 'ευ' δίφθογγον Δωρικῶς. Ἡ 'οι' ἐν ταῖς ὑπὲρ μίαν συλλαβὴν λέξεσι ψιλοῦται, εἰ μὴ τὸ 'μ' ἐπάγοιτο, οἷον οἶστρος, οἶκος· τὸ οἷος ἀναφορικὸν δασύνεται. τὸ οἷμος οἱμῶ δασύνεται. τὸ δὲ οἴμοι ἐπηύξηται ἀπὸ τοῦ οἴ ψιλουμένου. Ἡ 'ου' ἐν ταῖς ὑπὲρ μίαν συλλαβὴν λέξεσι ψιλοῦται, οὐρανός, οὐλή, οὐρῶ, οὖλος, οὐρός. οὕτω δὲ ἢ οὕτως δασύνεται. Τὸ 'ρ' ἀρχόμενον λέξεως δασύνεσθαι θέλει, ῥά, ῥανίς, ῥάξ χωρὶς τοῦ ᾿Ρᾶρος (ἔστι δὲ ὄνομα κύριον) καὶ χωρὶς τῶν ἐξ αὐτοῦ οἷον
αὔω, in the sense “to speak,” takes smooth breathing; but whenever it is used in the sense “to dry” or “to kindle,” then it must take rough breathing. The diphthong 'ει' takes smooth breathing, e.g. εἶδος, εἰκάζω, εἴρων and the rest, except εἱρκτή, Εἵλως “the slave,” and εἱκώς “the one who sent,” and εἱλίζω “to twist together,” and εἱλόμην, and εἷμα “the garment,” and εἱμένος “the clothed one,” and εἷνα “one,” and εἵποντο in place of ἠκολούθουν, and εἷσεν in place of ἐκάθισεν, εἱστήκει, and εἵως in place of ἕως, and εἵατο, and εἵλη “heat,” and εἱαμενή from the boiling of waters. Also marked is εἷς, the numeral. The diphthong 'ευ' takes smooth breathing, e.g. εὐλή, εὐλαί “the worms,” εὐδία, εὐθεῖα, εὐνή, εὐχή, εὖρος, εὔκηλος and the rest, except εὕδω “to sleep,” and εὕω “to set aflame,” and εὕρω, from which also εὑρίσκω. And εὗ in place of ἑαυτοῦ by crasis of 'ε' and 'ο' into the diphthong 'ευ' in Doric. The 'οι' in words of more than one syllable takes smooth breathing, unless 'μ' follows, e.g. οἶστρος, οἶκος; but οἷος, the relative, takes rough breathing. οἷμος, οἱμῶ takes rough breathing. But οἴμοι has been augmented from οἴ with smooth breathing. The 'ου' in words of more than one syllable takes smooth breathing: οὐρανός, οὐλή, οὐρῶ, οὖλος, οὐρός. But οὕτω and οὕτως take rough breathing. ῥ at the beginning of a word wants to take rough breathing: ῥά, ῥανίς, ῥάξ, except ᾿Ρᾶρος (it is a proper name) and except the derivatives from it, such as …