-in (ilgi hâli)

The genitive case (ilgi hâli) is primarily used to create a definite noun phrase, indicating a specific relationship between two nouns.

1. The Suffix Forms:
The suffix follows four-way vowel harmony:

• After consonants: -ın, -in, -un, -ün
• After vowels: -nın, -nin, -nun, -nün

2. Consonant Softening:
When adding the genitive suffix to a word ending in p, ç, t, or k, consonant softening occurs (e.g., kitap becomes kitabın, mutfak becomes mutfağın).

3. The Buffer Consonant:
Unlike most other cases that use -y-, the genitive uses a unique buffer consonant -n- when a noun ends in a vowel (e.g., araba-n-ın).

4. Usage and the 'Matching' Rule:

• In Noun Phrases: The genitive case acts as a trigger. In a definite noun phrase, the second noun must have a possessive suffix, as seen in benim evim (my house) or Ali'nin arabası.
• In Predicates: The genitive can stand alone to show ownership in a sentence without a verb, such as Bu anahtar Ahmet'in (This key is Ahmet's).
• With Postpositions: The genitive is used with words like için (for), gibi (like), or kadar (as much as) when following singular personal pronouns, the plural pronouns biz and siz, demonstrative pronouns, and the question word kim. For example: benim için, bizim gibi, bunun için, or kimin için. Note that the third-person plural pronoun onlar is an exception and stays in the plain form: onlar için, onlar gibi.
• In Subordinate Clauses: As you become proficient in complex sentences, you will see the genitive case used to mark the subject of nominalized clauses, such as in -dik structures (e.g., annem-in yaptığı pasta - the cake my mother made).

5. Irregularities and Special Cases:

• Irregular Pronouns: The first-person pronouns ben and biz are irregular, taking -im (benim, bizim).
• Demonstratives: When bu, şu, or o act as pronouns in the genitive, they require a pronominal 'n' before the suffix: bunun, şunun, onun. These are used to show possession for objects or people (e.g., bunun rengi - its color).
• The word 'Su': The word for water is a primary exception and uses a -y- buffer: suyun.
• Pronominal 'n': This is a standard morphological rule where the 'n' buffer is required before any case suffix (including the genitive) when it follows a third-person possessive suffix or the plural possessive -ları/-leri (e.g., onun arabası-n-ın rengi).
• The word 'Ne': The question word ne becomes neyin.
• Proper Nouns: Always use an apostrophe: İstanbul'un.