Turkish makes use of three buffer letters ‘n’ ‘y’ ‘s’. This is to keep vowels apart when adding suffixes.
The Buffer Letter ‘S’
Only used with the third person suffix -ı -i -u -ü he, she, it. It becomes -si -sı -sü -su when added to a root word which ends in a vowel. It is not used in any other instance.
kedi cat → kedisi [kedi-si] his / her cat
şemsiye umbrella → şemsiyesi [şemsiye-si] his / her umbrella
kapı door → kapısı [kapı-sı] his / her / its door
palto overcoat → paltosu [palto-su] his /her overcoat
ütü flat iron → ütüsü [ütü-sü] his /her iron
araba car → arabası [araba-sı] his / her car
kuzu lamb → kuzusu [kuzu-su] his / her lamb
The Buffer Letter ‘Y’
The buffer letter ‘y’ is only used with simple nouns. Buffer ‘y’ is used on plain simple unsuffixed nouns with the direct object condition suffix -i (meaning ‘the’). It becomes -yi -yı -yu -yü when added to a root word which ends in a vowel.
kedi cat → kediyi [kedi-yi] the cat
banka bank → bankayı [banka-yı] the bank
The buffer letter ‘y’ is also used on plain simple unsuffixed nouns with the the movement toward condition [dative] -a, -e (meaning ‘to, towards’). It becomes -ya -ye when added to a root word which ends in a vowel.
kedi cat → kediye [kedi-y-e] to the cat
banka bank → bankaya [banka-y-a] to the bank
baba father → babaya [baba-y-a] to the father
The Buffer Letter ‘N’
With the Ownership Condition
Buffer letter ‘n’ is always used for the ownership condition [genitive] -in -ın -ün -un. It becomes -nin -nın -nün -nun for “owners” that end in a vowel. Bare nouns in the ownership condition do not use ‘y’ as a buffer letter.
köprünün [köprü‑nün] of the brıdge, the bridge’s
köprüsünün [köprü‑sü‑nün] of his brıdge, his bridge’s
masanın [masa‑nın] of the table, the table’s
masalarının [masa‑ları‑nın] of their table, their table’s
pencerenin [pencere‑nin] of the window, the window’s
penceresinin [pencere‑si‑nin] of its window, its window’s
yolcunun [yolcu‑nun] of the traveller, the traveller’s
yolcularının [yolcu‑ları‑nın] of their traveller, the traveller’s
With Already Suffixed Nouns
This shift of buffer letter ‘y’ to ‘n’ enables the listener to discern that the word is already agglutinated (extended) by previous suffixes. Buffer letter ‘n’ is used on already suffixed nouns.
kedisi his/her cat → kedisini [kedi-si-ni] his/her cat [3rd person possessed object]
bankası his/her bank → bankasını [banka-sı-nı] his/her bank [3rd person possessed object]
kedileri their cat → kedilerine [kedi-leri-ne] to their cat [3rd person plural possessed motion toward]
With -da/-de and -dan/-den
The suffixes -de and -dan are added directly to basic nouns, for example:
kedi cat → kedide [kedi-de] on the cat
kedi cat → kediden [kediden] from the cat
kapı door → kapıda [kapı-da] on / at the door
kapı door → kapıdan [kapıdan] from the door
They become -nda/-nde and –ndan/-nden when added to already suffixed nouns. This is to separate them from the extended word:
kedisi his/her cat → kedisinde [kedi-si-nde] on his/her cat
kedisi his/her cat → kedisinden [kedi-si-n-den] from his/her cat
kapısı his/her door → kapısında [kapı-sı-nda] on/at his/her door
kapısı his/her door → kapısından [kapı-sı-n-dan] from his/her door