"e and i are non-labial (palatal) vowels of the front zone; e is a vowel of  middle rise, i of high rise; o and u are labial vowels of the back zone; o is a vowel of low or middle rise, u of high rise; a is a non-labial vowel of the middle (from another point of view back) zone and low rise" (Besarion Jorbenadze. The Kartvelian Languages and Dialects. Tbilisi: Mecniereba, 1991, p.42).

"O may have low as well as middle highness (rise). The correlation low - middle rise in this case is not relevant because labial (rounded) o differs from nonlabials - low a and middle e - with labialness. Low - middle highness is a relevant feature for nonlabials a and e. Otherwise their articulation would have coincided. Thus, the relevant features for the Georgian vowel system are the highness (rise) and labialness". (Tevdore Uturgaidze. Kartuli enis ponemat'uri st'rukt'ura [The Phonemic Structure of the Georgian Language], Tbilisi: Mecniereba, 1976, p.11).