The English preposition for has several meanings, each of which is represented by a separate preposition in Russian. This page discusses the different meanings of the English preposition and associates those meanings with the corresponding Russian preposition and case.
1. Recipient (Experiencer) = Dative case alone
To indicate the recipient of an object or condition, in either the concrete or abstract sense, use the dative case alone. купить себе новую шляпу. buy a new hat for oneself. подарок мальчику. gift for a boy. письмо тебе. a letter to/for you. Холодно мне. It's cold to/for me.
2. Benefit = для + Genitive
To express "for" in the sense of "for the benefit of", use the preposition для plus the genitive case. Она сделала это для меня. She did that for me. Он открыл дверь для тёти. He opened the door for his aunt.
3. Exchange/Replacement = за + Accusative
If for means "in exchange for something)" or "in place of someone", use за and the accusative case. Спасибо за помощь. Thanks for the help. Плати за билеты. Pay for the tickets. Он дал учебник за словарь. He swapped his text for a dictionary. Он это сделал за меня. He did that for (instead of) me.
4. Temporal "for" (Duration of Action) = Accusative case alone
If the phrase meaning "for" indicates of the duration of the action referred to by the verb or the repetition of the action, use the accusative case alone. Она читала три часа. She read (for) three hours. Он работал там два месяца. He worked there (for) two months.
5. Temporal "for" (Duration after Action) = на + Accusative
To indicate the duration of a period of time occurring after the completion of the action referred to by the verb, use на plus the accusative case. Он поехал в Москву на неделю. He drove to Moscow for a week. Она вышла на минуту. She went out for a minute. Его послали туда на день. He was sent there for a day.
6. "To get" = за + Instrumental
Where 'for' means 'to get' in the sense that 'he went for the newspaper' means 'he went to get the newspaper', use за plus the instrumental case in Russian. Она вышла за газетой. She went out for (to get) a paper. Он заехал за мной. He stopped by for me. Он пошел за бензином. He went for (to get) gasoline.
7. "For / Against" = за + Accusative / против + Genitive
For in the sense of support, e.g. I'm for peace means "I support peace", where for is the antonym of against, use за plus the accusative case. Я за всеобщее разоружение. I'm for general disarmament. Я не против него. I'm not against it.
8. "For" in setting a deadline = на + Accusative
For in the sense of a deadline or due date is expressed by на+Acc. задание на завтра the assignment for tomorrow мой план на лето my plan(s) for the summer
Now that you have studied the rules and examples, let's see how well you can detect the various sense of English for in Russian.
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1996 Robert Beard