Learn Turkish: Adam bu daktilo ile mektup yazıyordu. - The man was writing a letter with this typewriter.

This verb combines two suffixes you already know to form the past continuous tense. First, we take the verb root yaz- (write) and add the present continuous suffix -ıyor (writing). Then, we add the past tense ending -du (was). Together, yazıyordu means "he/she/it was writing."

Why is it just mektup and not mektubu (with the accusative case)?

We only use the accusative case (like mektubu) when referring to a specific direct object (like "the letter"). Because he is just writing "a letter" (a general, indefinite object), it stays in its plain dictionary form: mektup.

Why does mektup come right before the verb, instead of earlier in the sentence?

In Turkish, when a direct object is indefinite and doesn't have a case ending (like mektup meaning "a letter"), it must be placed directly in front of the verb. Therefore, the phrase bu daktilo ile (with this typewriter) has to come before it.

Could I attach ile directly to daktilo instead of writing it as a separate word?