Breakdown of Он звонил дважды за вечер.
он
he / it (for a masculine noun) / it (for a neuter noun)
звонить
to call
вечер
evening
дважды
twice
Questions & Answers about Он звонил дважды за вечер.
Why is the imperfective verb звонил used instead of the perfective позвонил? Weren't the calls completed?
Even though the calls were completed, the imperfective aspect is used here because the action was repeated (дважды). Just as you use imperfective verbs like бывать for habitual or recurring actions, you generally use imperfective verbs for actions repeated a specific number of times in the past, focusing on the repetition itself rather than a single final result.
Is there a difference between дважды and два раза?
No, they mean the exact same thing. Дважды is a single adverb meaning twice, while два раза literally means two times. You can use them interchangeably in this sentence, though дважды is slightly more concise.
Why does the sentence use за вечер to mean in one evening?
To express that an action happened within a specific time frame or over the course of a period, Russian uses the preposition за followed by the accusative case. Here, за вечер shows that the two phone calls occurred within the span of that single evening.