Özet:

In Turkish, the monophthongs are a, e, ı, i, o, ö, u and ü. However, diphthong is not found as a phoneme in Turkish. In its simplest definition, a diphthong is a compound sound in a syllable which starts with a vowel and ends with another one. Yet, in some phonetic positions in Turkish, it is possible to see the emergence of diphthongs like ou, ei, öü etc. and therefore the occurrence of diphthongisation. Given this, it should be indicated that there are some important problems in the investigation of the diphthongs in the field of Turcology. First, diphthongs have been confusingly conceptualised in the scholarly literature through different forms like ikiz ünlü, kayan ünlü and çift ünlü. Moreover, many researchers have ignored the fact that the most essential criterion of diphthongs is to form a single syllable. Lastly, the two vowels existing side by side in some words borrowed from other languages lead the researchers to characterise them as diphthong since they confuse spelling and pronunciation. These problems in the scholarly literature have certainly necessitated the writing of a theoretical study on diphthongs in Turkish. In this context, this article primarily reviews the literature on diphthongs and then it discusses diphthongisation with special reference to the /ğ/ phoneme in Turkish. Moreover, the article focuses on the matter how the words borrowed from English containing diphthongs have been adapted to the phonetic structure of Turkish.