Abstract: The present study applies to the /i/ status in Turkish and Kazakh in the field of phonology and phonetics. Turkish and Kazakh are both Turkic languages with a common origin. This study aims to explain the difference between the acoustic realization of the /i/ proto-phoneme in Turkish and Kazakh by analyzing the historical development of the phoneme and its modern acoustic characteristics in both languages. The comparison of acoustic and articulation peculiarities of [i] in Turkish and Kazakh reveals the difference in the movement of the speech organs in these languages. Different tongue movements make realizations of /i/ in the languages to sound different. Analysis of texts which is done in the framework of this study showed that this difference existed during at least 150 years. Moreover, as it is shown in the study it is typical not only for the realizations of the /i/ phoneme but also for realizations of other phonemes in Turkish and Kazakh. However, in spite of the different acoustic characteristics the /i/ phoneme is understood easily by native Turkish and Kazakh speakers. This fact is analyzed at the end of the article. The actual reason for the difference between Turkish and Kazakh languages is contained in the field of the issue that makes this articulation difference existent.

Keywords: Old Turkic, speech organs, pronunciation habits, articulation system, consonant, vowel, Kazakh, Turkish, proto-phoneme, вокальная система