Changes which occur in the phonetic structure of a language are called phonetic events. One of the reasons for phonetic change is contamination in which a word or form influences another word or form and a different form with common features arises. In earlier periods when Turkish was written in Arabic letters, the fact that the Arabic letters “vav” and “ya” corresponded to both vowel and consonant phonemes caused there to be some different pronunciations in Arabic and Persian words. In other words, the letter “ya” which is expected to be pronounced as a vowel is pronounced as a consonant, and the letters “vav” and “ya” are pronounced as vowels although they are expected to be pronounced as consonants. As a result of these variant pronunciations, some words evolved into forms that are different from the corresponding words in their original language. Phonemes such as “g” and “nasal n” which are not found in the Arabic alphabet are counterbalanced in the Ottoman alphabet with “kâf-i Farisî” borrowed from the Persian alphabet and “kâf-i nûnî” which Turks developed. But these phonemes were written with Arabic kef in manuscripts due to greater ease of writing. In some Turkish words which include these phonemes and which are used in some Arabic dialects, different pronunciations exist due to the fact that the mentioned phonemes in the Arabic alphabets are written with the letter kef. The reason for these phonetic events which are based on contamination is the system of vowel points in the Arabic alphabet. As some words written with the same letters were developed with different vowel points, synonymous words came into existence. It is in fact contamination which determines the direction of all phonetic events that emerge in these words undergoing phonetic events through different reasons. The reason for contamination in those events is the Arabic alphabet, that is, writing in more general terms. The fact that phonetic events arise firstly in spoken language indicates that it is not the typical characteristic of writing to cause phonetic events although this is possible. Examples that belong to the period of Old Anatolian Turkish and that undergo this kind of phonetic event are given in the study.