Vowel Harmony
In Turkish, words are constructed in such a way that the vowels follow a specific pattern. This pattern is called Vowel Harmony and is an important feature of the Turkish language. Vowel Harmony is used particularly when deciding which vowels should be used when adding a suffix to a word. By looking at a particular vowel in a word (usually the last vowel), the rules of Vowel Harmony help us to decide which vowels will be used after it. In order to understand Vowel Harmony we have to look at the different types of vowels that exist in Turkish:

Vowels: a, e, ı, i, o, ö, u, ü

Hard vowels: a, ı, o, u
Soft vowels: e, i, ö, ü

Straight vowels: a, e, ı, i
Round vowels: o, ö, u, ü

There are four Vowel Harmony rules in total: two Major Vowel Harmony and two Minor Vowel Harmony rules.

MAJOR VOWEL HARMONY
Part 1: Hard vowels

If the last vowel of a word is one of a/ı/o/u, vowels in the suffixes that follow it can only be one of a/ı/o/u.

a / ı / o / u ➨ a / ı / o / u
Part 2: Soft vowels

If the last vowel of a word is one of e/i/ö/ü, vowels in the suffixes that follow it can only be one of e/i/ö/ü.

e / i / ö / ü ➨ e / i / ö / ü
MINOR VOWEL HARMONY
Part 1: Straight vowels

If the last vowel of a word is one of a/e/ı/i, vowels in the suffixes that follow it can only be one of a/e/ı/i.

a / e / ı / i ➨ a / e / ı / i
Part 2: Round vowels

If the last vowel of a word is one of o/ö/u/ü, vowels in the suffixes that follow it can only be one of a/e/u/ü.

o / ö / u / ü ➨ a / e / u / ü