Understanding when to choose the perfective or the imperfective form of a verb is a challenge for most learners of Russian. There is some play between the two forms in this excerpt from Мастер и Маргарита. Can anyone comment on reasons why the author did this?
– А тебя предупредили по телефону, чтобы ты их никуда не носил? Предупреждали, я тебя спрашиваю?
– Предупрежди… дали… дили… – задыхаясь, ответил администратор.
It’s not a play between the two forms, just an attempt to represent nervous speech. In some cases, perfective and imperfective aspects can be used interchangeably, so the first guy asks the same question twice (first using perfective then imperfective), and the second guy, being nervous and scared, mixes up two forms, starts with impossible “предупрежди-” , and finally corrects himself using both possible endings.
предупредили - happened once (or it was happening many times but the result is the same)
Предупреждали - happened regularly
Not necessarily, предупреждали can be used to describe a single action as well. In fact, I can’t think of any example for this verb where perfective/imperfective forms couldn’t be used interchangeably.
Yes, both words may be used interchangeably with slight nuances.