# Why decline неделя in "В неделю"?

Why decline неделя in "В неделю"? And not день or год in "В год" and "B день"

And what should be the case? i would expec the prepositional case to decline, but is looks reather that it was declined in acusative case. Why use this case?

It is accusative case in all the examples. Accusative case of год and день coincides in form with Nominative, while Accusative of неделя does not.

And what should be the case?

Depends on what meaning you want. It can be Accusative, Prepositional, Locative, depending on context.

• Yes, from a learner's point of view, most time expressions just need to be memorized without worrying about the 'logic' of using a particular case. Here's one way to keep them straight - periods of a day or less: в + acc. (в среду, в этот день, в тот час, в эту секунду); weeks: на + prep. (на этой неделе); longer than a week: в + prep. (в этом месяце, в этом году, в девятнадцатом столетии).
– Curt
Nov 16, 2016 at 15:49
• @Curt or improve your feel of logic beyond what you read in textbooks. Nov 16, 2016 at 15:54
• @Anixx - not sure what you mean; but any explanation of the logic here (which I've never felt, as a non-native speaker) is welcome. ))
– Curt
Nov 16, 2016 at 15:58
• You might find this (affiliated) link useful russian.morpheem.com/form/time-phrase we tried to systematically explain which preposition (в, на, по, none at all) you should use, with which case (accusative, prepositional or locative), with which words (for example, неделя, месяц and пятница behave differently), and what meaning you get in the end when all those factors are assembled. Click around! Hope it helps. I'm sorry to say that the full answer to your question is too voluminous to include here. Nov 18, 2016 at 9:20

You can say:

• В году, в сутках, в неделе. В году у нас 365 дней. В сутках 24 часа. В неделе 7 дней.

You can decline the way you say but it will be like:

• Мы ходим туда один раз в неделю.
• Мы летаем в Москву дважды в год.
• Это явление произошло точно день в день, как и было предсказано.
• Его нет дома уже третьи сутки.