Nutt. E. M. Geldart (1870): The Modern Greek Language In Its Relation To Ancient Greek (reprint 2004, Lightning Source Inc. ). G. N. Hatzidakis (1902): Ἀκαδημαϊκὰ ἀναγνώσματα: ἡ προφορὰ τῆς ἀρχαίας Ἑλληνικῆς ("Academic Studies: The pronunciation of Ancient Greek"). A. Meillet (1975) Aperçu d'une histoire de la langue grecque, Paris: Librairie Klincksieck (8th edition). A. Meillet & J. Vendryes (1968): Traité de grammaire comparée des langues classiques, Paris: Librairie Ancienne Honoré Champion (4th edition). E. Schwyzer (1939): Griechische Grammatik, vol. 1, Allgemeiner Teil. Lautlehre. Wortbildung. Flexion, München: C.H. Beck (repr. 1990 ). W. B. Stanford (1967): The Sound of Greek. Ancient Greek sources Aristotle All speech consists of these categories: element [letter], syllable, conjunction, noun, verb, inflection, phrase. A letter is an indivisible sound — not any sound, but a sound from which a compound sound [syllable] can naturally be made, since the sounds of animals are also indivisible, and I call none of them a letter. The categories of sound are sounding [vowels], half-sounding [semivowels: fricatives and sonorants], and unsounded [silent or mute: stop]. These categories are the vowel, which has audible sound but no contact [between lips or between tongue and the inside of the mouth]; the semivowel, which has audible sound and contact (for example s and r); and the mute, which has contact and no sound by itself, becoming audible only with [letters] that have a sound (for example g and d). [Letters] differ in the shape of the mouth and place [in the mouth], in thickness and thinness [aspiration and unaspiration], in length and shortness — and still more in sharpness and depth and middle [high and low pitch, and pitch between the two]: but theorizing about them in detail is the job of those who study [poetic] meter. Dionysius Thrax There are 24 letters, from a to ō.... Letters are also called elements [of speech] because they have an order and classification. Of these, seven are vowels: a, e, ē, i, o, y, ō. They are called vowels because they form a complete sound by themselves. Two of the vowels are long (ē and ō), two are short (e and o), and three are two-timed (a i y). They are called two-timed since they can be lengthened and shortened. Five are prefixable vowels: a, e, ē, o, ō. They are called prefixable because they form a complete syllable when prefixed before i and y: