Перед сном я зайду на кухню и выключу свет.

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Breakdown of Перед сном я зайду на кухню и выключу свет.

• на: to
• и: and
• перед: before

Questions & Answers about Перед сном я зайду на кухню и выключу свет.

Why is it перед сном and not перед сон or перед сна?

Because перед (like передо) governs the instrumental case.
So сон (sleep) becomes instrumental сном.

• сон (nom.) → сна (gen.) → сну (dat.) → сном (instr.)
• перед чем? = перед сном = before sleep / before going to bed

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Does перед сном mean before sleeping or before going to bed?

In everyday Russian, перед сном commonly means before going to bed / before bedtime (i.e., as part of the bedtime routine), not necessarily literally “while you are already falling asleep.” Context decides, but this phrase is strongly associated with bedtime habits.

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Why is зайду used here? What verb is it from?

зайду is the 1st person singular future form of the perfective verb зайти.
It literally implies to drop in / to step in (briefly), often with the nuance of stopping by on the way.

So я зайду на кухню is like I’ll pop into the kitchen (not “I will go to the kitchen and stay there”).

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