Accusative: definite or not?

A direct object gets the accusative ending -ı/-i/-u/-ü only when it is definite, a specific thing the listener can identify:

• with bu, şu, o: bu kitabı (this book), şu çayı (that tea)
• with names: Ayşe'yi, İstanbul'u
• with a description that points to one thing: masadaki ekmeği (the bread on the table)

An indefinite or general object stays in the bare form: bir elma yedim (I ate an apple), kitap okurum (I read books), iki bilet aldım (I bought two tickets).

After a vowel add a buffer y: elmayı, soruyu. Many words ending in p or k soften: kitap → kitabı, mektup → mektubu, ekmek → ekmeği. Names keep an apostrophe: Mehmet'i.