English translation by Bruna Pogliano

The term diphthong, in Greek δίφθογγος συλλαβή, two-vowel sound syllable, is used to describe a combination of two consecutive vowels which areperceived like a single-vowel sound emission, owing to the sound quality characterizing them. This happens when an open vowel (α ε η ο ω) is followed by a close vowel (ι υ) or else when υ is followed by ι.

Remember that the two vowels of a diphthong are always part of the stem word and never result from adding an ending to the stem word, while all other combinations of vowels produce specific phonetic outcomes (crasis, contraction, elision, aphaeresis or inverse elision).

Traditionally, diphthongs are classified as proper and improper. Diphthongs are called proper when the first vowel is either short or followed by υ, while diphthongs consisting of a long vowel followed by ι are called improper.

In ancient times iota was both written and pronounced, but it gradually became silent and was consequently omitted in writing. During the Byzantine era, classical texts were copied and great attention was paid to spelling in an attempt to make it as accurate as possible and to avoid any ambiguities or inaccuracies. This system, called μεταχαρακτηρισμός, was characterized by supplementing breathing marks and accents to all words, by separating words with spaces and by restoring iota to improper diphthongs. The practice of writing iota subscript was developed in this age; it then spread as a solution to balance the fact that iota was no longer pronounced with the need to record the original spelling of classical texts. This is the reason lower case ᾱ η ω, when followed by ι, are usually written ᾳ ῃ ῳ instead of αι ηι ωι, with few exceptions, where such spelling is the result of editorial decisions. On the contrary, when the first vowel of an improper diphthong is capitalized, iota is still written on the line, after the long vowel; it is then called iota adscript. It has to be kept in mind that neither iota subscript nor iota adscript are sounded in scholastic pronunciation.

With regard to accents, when stressed, proper diphthongs carry the accent mark over the second vowel, but it is the first vowel that has to be stressed. For example: the conjunction καί (= and) carries the stress mark overι, but it is pronounced kái. Likewise, both rough and smooth breathing marks are placed over the second vowel of proper diphthongs.

Lower-case improper diphthongs with iota subscript carry accent and breathing marks over the vowel; if stressed, upper-case improper diphthongs carry accent and breathing marks to the left of the first vowel.

The following table shows ancient Greek diphthongs. Practice adding accent and/or breathing marks, just click on the buttons to the right and you will see them properly placed. Accent marks cannot be added to upper case diphthongs prior to breathing marks, for upper case diphthongs are always in the initial position, thus having necessarily to carry smooth or rough breathings.

Type Open vowel Close vowel Diphthong Add
lower case upper case
Proper diphthongs
αι Αι
αυ Αυ
ει Ει
ευ Ευ
οι Οι
ου Ου
η υ ηυ Ηυ
υ + ι
υι Υι
Improper diphthongs