Aspect: now, habit or done once

Almost every Bulgarian verb comes in a pair: an imperfective verb for a process or a habit, and a perfective verb for one complete act with a result: пиша / напиша, купувам / купя, идвам / дойда.

• Present, now or habit: always the imperfective. Сега пиша писмо (I'm writing a letter now). Всеки ден купувам хляб (I buy bread every day). A perfective present never stands alone in a main clause.
• One finished act in the past: the perfective in the aorist. Cues: най-после, цялата, за два часа, изведнъж. Вчера прочетох цялата книга (Yesterday I read the whole book).
• Habit or background in the past: the imperfective in the imperfect. Като малък често отивах на село (As a child I often went to the village).

In the gap the imperfective always comes first.