Mektubu hatasız yazdım.

I wrote the letter without errors.

Breakdown of Mektubu hatasız yazdım.

• yazmak: to write
• mektup: the letter
• hatasız: without errors

Questions & Answers about Mektubu hatasız yazdım.

Why does mektup become mektubu?

Because Turkish marks definite direct objects with the accusative suffix. Adding -u to mektup (giving mektubu) shows you wrote the letter (not just any letter).

What does the suffix -sız in hatasız mean?

The derivational suffix -sız means “without.” So hatasız literally means “without mistakes” or “errorless.”

Why is it hatasız and not hatasiz, hatasuz, or hatasüz?

Turkish vowel harmony makes the vowel in -sız match the last vowel of hata (which is a, a back vowel). Thus you use -sız.

Is hatasız acting as an adjective or an adverb here?

Morphologically it’s an adjective, but because it’s describing how you wrote, it functions as an adverb (i.e. errorlessly).

Why doesn’t hatasız take the adverbial suffix -ca (as in hatasızca)?