Choosing the Right Aspect
Прави глаголски вид — See an action as a process, a habit or a completed result.
Process and result
Imperfective verbs show activity or repetition: читати, писати. Perfective partners present one bounded result: прочитати, написати.
Читао сам књигу, али је нисам прочитао.
I was reading the book, but I did not finish it.
Habit or one occasion
Words such as сваког дана and често normally call for an imperfective verb. A single completed action with јуче or коначно often calls for a perfective one.
Сваког дана сам писао, а јуче сам написао крај.
I wrote every day, and yesterday I wrote the ending.
Starting and continuing
почети, престати and наставити are naturally followed by да + present, usually imperfective because the following activity is viewed in progress.
Почела је да учи српски.
She started learning Serbian.
Commands choose a viewpoint
A positive command often targets a result: «Отвори прозор.» A general negative warning normally blocks the activity: «Не отварај прозор.»
Немој да отвараш врата.
Do not open the door.
Repeated completed acts
Some verbs have a secondary imperfective for repeated results: потписати once, потписивати repeatedly. Context, not an English tense, selects the aspect.
Директор сваког јутра потписује документе.
The director signs documents every morning.
Put It Together
Keep the lesson goal in view: See an action as a process, a habit or a completed result. Revisit the examples, then test yourself in practice.