but a de jure autonomous entity within Georgia), where it is the official language, and an unknown number of speakers in Turkey. It has been a literary language from the beginning of the 20th century. Abkhaz and Abaza may be said to be dialects of the same language, but each preserves phonemes which the other has lost. Abkhaz is characterised by unusual consonant clusters and one of the world's smallest vowel inventories: It has only two distinctive vowels, an open vowel /a/ and a mid vowel /ə/. Next to palatalized or labialized consonants, /a/ is realized as [e] or [o], and /ə/ as [i] or [u]. There are three major dialects: Abzhuy and Bzyp in Abkhazia and Sadz in Turkey. Abaza Abaza has some 45,000 speakers, 35,000 in Russia and 10,000 in Turkey. It is a literary language, but nowhere official. It shares with Abkhaz the distinction of having just two phonemic vowels. Abaza is phonologically more complex than Abkhaz, and is characterised by large consonant clusters, similar to those that can be found in Georgian. There are three major dialects, Tapant and Ashkhar. Some are partially intelligible with Abkhaz. Ubykh Ubykh forms a third branch, with parallels to both Adyghe and Abkhaz. The population switched to speaking Adyghe, and Ubykh became extinct on 7 October 1992, with the death of Tevfik Esenç. A dialectal division within Ubykh was suspected by Georges Dumézil, but the divergent form he described in 1965 was never investigated further. With eighty-one consonants, Ubykh had perhaps the largest inventory in the world aside from the Kx'a and Tuu families of southern Africa with their extensive system of clicks. There are pharyngealised consonants and a four-way place contrast among sibilants. It was the only Northwest Caucasian language never to have a literary form. Relationship to other language families A number of factors make the reconstruction of the Northwest Caucasian proto-language problematic: most roots in Northwest Caucasian languages are monosyllabic, and many are single consonants; the sound changes are often intricate, and the numerous consonants and sibilant contrasts provide further complexity; ablaut was extensive and still plays some part in the modern languages; borrowings between languages of the family were frequent; extensive homophony occurs in the modern languages. For these reasons, Proto–Northwest Caucasian is widely accepted as being one of the most difficult proto-languages to deal with, and it is therefore more difficult than most to relate