Vowel harmony (ünlü uyumu) is a cornerstone of Turkish grammar. It dictates that vowels within a word, including its suffixes, must belong to the same class. This makes Turkish sound melodic.

1. Major Vowel Harmony (Büyük Ünlü Uyumu / Two-fold Harmony / A-Type Harmony):

This rule divides vowels into two groups:

• Back vowels: a, ı, o, u
• Front vowels: e, i, ö, ü

A Turkish word will generally contain EITHER all back vowels OR all front vowels. Suffixes change to match the last vowel of the stem.

Example: The plural suffix can be:

• -lar (if the last vowel of the stem is a back vowel): kitap → kitaplar (books), oda → odalar (rooms)
• -ler (if the last vowel of the stem is a front vowel): ev → evler (houses), göz → gözler (eyes)

2. Minor Vowel Harmony (Küçük Ünlü Uyumu / Four-fold Harmony / I-Type Harmony):

This harmony considers both front/back and unrounded/rounded properties. It primarily affects suffixes that require a high vowel (ı, i, u, ü).

• If the last vowel of the stem is a, ı → the suffix vowel becomes ı. Example: kapı + -ı (accusative) → kapıyı; kapı + -da (locative) → kapıda (at the door)
• If the last vowel of the stem is e, i → the suffix vowel becomes i. Example: ev + -i (accusative) → evi; ev + -de (locative) → evde (at home)
• If the last vowel of the stem is o, u → the suffix vowel becomes u. Example: okul + -u (accusative) → okulu; okul + -da (locative) → okulda (at school)
• If the last vowel of the stem is ö, ü → the suffix vowel becomes ü. Example: köy + -ü (accusative) → köyü; köy + -de (locative) → köyde (in the village)

Importance:

Understanding and applying vowel harmony is crucial for correctly forming words and using suffixes in Turkish.