Breakdown of По истечении срока вам придётся купить новый билет.
вы
you (plural)
новый
new
билет
ticket
купить
to buy (perfective)
Questions & Answers about По истечении срока вам придётся купить новый билет.
Why does истечении end in -ии here, and what case is it?
It is in the prepositional case. In formal contexts, the preposition по meaning "upon" or "immediately after" requires the prepositional case. Because the dictionary form истечение (expiration) is a neuter noun ending in -ие, its prepositional ending is -ии rather than the standard -е.
Is по истечении срока a common everyday phrase, or is it highly formal?
It is quite formal and is typically found in legal, business, or official contexts (like ticket rules, contracts, or visas). In casual everyday speech, a Russian speaker would be much more likely to say когда срок закончится (when the time is up).
Why use the construction вам придётся instead of вы должны будете?
Вам придётся uses the dative case (вам) with the future form of the verb прийтись. It emphasizes a circumstantial necessity, meaning "you will be forced to" or "circumstances will dictate that you must" buy a ticket. Вы должны будете is also correct but can sometimes imply a personal duty or moral obligation rather than just a situational requirement.
Why is срок in the genitive case (срока)?
It modifies the noun before it (истечение), expressing "expiration of the term" or answering "expiration of what?". In Russian, this "of" relationship linking two nouns is handled by putting the second noun in the genitive case.