As a language of civilization and culture, Turkish is one of the languages used in some of the oldest written documents in the world.Turks have established states in vast geographies throughout history and have been in contact with many societies. This contact has resulted in some exchanges in almost every field. One of the most important of these exchanges is undoubtedly the exchange of language. In addition to the vocabulary and grammatical structures, it is seen that foreign alphabets are also borrowed in several occasions. The Turkish language has undergone many alphabet changes from the 7th-8th centuries, which we can follow through written texts. When both the Köktürk alphabet and the alphabets taken from other societies are examined, it is seen that these alphabets are insufficient to meet the needs of the Turkish language and do not reflect its subtleties, especially until the beginning of the 20th century. Today, it is sometimes impossible to determine the historical development and change of some sounds due to the inadequacies of alphabets, especially in phonetics studies. In addition to this, how to transcript the loanwords and grammatical structures is another challenge. Although transcription unity has been achieved to a great extent in Turcology studies, some issues have not been resolved yet or were overlooked. The point we would like to focus on is the labial harmony in Persian noun and reference phrases as well as how to show the sound changes that occur due to this harmony in the translated text. There is no clear consensus concerning the labialization of the unrounded vowel that forms the phrase in Persian noun phrases (āb-u ḥayvān, ḥüsn-ü ẓan, dürr-ü yetḭm etc.) and how to spell the utterance and spelling formed by the delabialization of the connecting preposition in Persian reference phrases (baş ı cān, ṣaġ ı ṣol, ḥaḳḳ ı bāṭıl etc.) in the translation studies. Some researchers try to correct these sound events by attributing them to the ignorance of the authors and copyists, while researchers reflect these issues in their studies, albeit partially. In the studies we have made, it is understood that labial harmony in Persian noun and reference clauses started to be seen at the latest from the 15th century and intensified in the 17th and 18th centuries, when the labial harmony was seen intensely in Turkish. In fact, in our opinion, this situation has affected the general orthography in some dialects and has become common orthography. We think that sounds that should not be rounded or unrounded, such as ḳarż-u ḥasen, Cibrḭl-ü emḭn, selāṭḭn-u cihān, luṭf ı ḳahr,rūz ı şeb, Mecnūn ı Leyla etc, and so on, become rounded and unrounded by the effect of general orthography and by analogy. This situation, which has hundreds of examples from the 14 manuscripts that we have the opportunity to examine in our study, cannot be explained as the ignorance or negligence of the authors or copyists. On the contrary, it turns out that this situation is a normal phonetic event in the historical development process of the Turkish language. This is because it is very difficult to say that the same mistake is repeated in dozens of works and hundreds of examples written by different authors or copyists in different centuries in different geographies. Moreover, in the samples we have identified, the existence of sounds that affect the sound change phonetically, that is, have a rounding or unrounding effect, is also seen.

We have identified many examples from the 14 different manuscripts included in the study. However, we did not include all of the examples. We selected the examples repeated the most in the same work. Despite our desire to show the frequency of use by illustrating all examples found, we aimed to reveal the prevalence of labial harmony in Persian noun and reference phrases by taking a selection of different examples in order not to exceed the size of the article. However, when the same example occurs in different works, we try to include it in our study in order to show the frequency of use. As we have stated above, the issue we have mentioned has attracted the attention of some researchers. Since we did not have the opportunity to reach all of the manuscripts tacling this issue, we did not include examples that we could not witness in our work. Therefore, the examples given here present only part of the examples found in the literature. It is certain that the number and variety of examples related to the subject will increase depending on the number of works to be scanned. In this article, the labial harmony occurring in Persian noun and reference phrases will be examined and suggestions will be given about how the orthography, which is formed due to labial harmony, should be shown in the translated text.