Breakdown of Саш, Катя плачет, присмотри за сестрой!
сестра
sister
плакать
to cry
Саша
Sasha
присмотреть за
to keep an eye on (pf)
Questions & Answers about Саш, Катя плачет, присмотри за сестрой!
Why is the name written as Саш instead of Саша?
This is the colloquial truncated vocative case, which is the focus of your current lesson. When addressing someone informally, Russians often drop the final -а or -я from names and kinship terms. Саша becomes Саш, which makes the speech sound more natural and affectionate among family.
If we shorten Саша to Саш, why don't we shorten Катя to Кать here?
Because Katya is not the person being spoken to. The truncated vocative form is strictly used for direct address. Here, Sasha is being addressed, while Katya is the grammatical subject of the clause (Катя плачет - Katya is crying), so her name must remain in the standard nominative case.
Why does присмотри take the preposition за plus the instrumental case (сестрой)?
The verb присмотреть (to look after / to keep an eye on) governs the preposition за followed by the instrumental case. This is a set verb pattern you have to memorize. It is somewhat similar to how we say 'look AFTER' in English, but the Russian phrasing translates literally closer to 'watch BEHIND'.
Could I use the imperfective imperative присматривай instead of the perfective присмотри?