How does vowel harmony work in Turkic languages?

In Turkic languages, vowel harmony is a fundamental phonological feature that dictates the structure of words and their suffixes. It ensures that words generally consist of syllables produced with a consistent tongue position, either front or back.1

There are two primary types of vowel harmony in these languages:

• Palatal Harmony: This is based on the distinction between front vowels (e, i, ö, ü) and back vowels (a, ı, o, u). Within a word, all vowels typically belong to the same class. Consequently, suffixes must vary to match the vowel class of the primary stem. For example, in Turkish, the locative suffix appears as -de after a front-vowel stem (ev-de, "in the house") but as -da after a back-vowel stem (oda-da, "in the room").12
• Labial Harmony: Most Turkic languages also employ labial harmony, which governs the rounding of vowels between syllables. This ensures that vowels agree in terms of being rounded or unrounded.1

While these rules are highly regular, their application can vary across different languages and dialects, sometimes influenced by contact with other language families.1