Ночью я сплю спокойно.

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Breakdown of Ночью я сплю спокойно.

• ночь: the night
• спать: to sleep
• спокойно: peacefully

Questions & Answers about Ночью я сплю спокойно.

Why is the word ночью used instead of the dictionary form ночь?

In Russian, the noun ночь (night) takes the instrumental case (ночью) when you want to say “at night.” This case form turns the noun into an adverbial expression of time. You wouldn’t say ночь я сплю спокойно, because ночью specifically conveys “during the night.”

Why is there no preposition like в before ночью?

For parts of the day, Russian typically drops the preposition and uses the case ending alone. So you get утром, днём, вечером, ночью. Adding в ночью would be ungrammatical. If you really need a preposition, you’d use the genitive (в ночь) in rare poetic contexts, but the normal everyday form is ночью without в.

Can I omit the pronoun я since the verb сплю already shows “I”?

Yes. Russian verbs are conjugated to show their subject, so you can say simply Ночью сплю спокойно and it’s perfectly fine. Including я adds slight emphasis or clarity (“I, specifically, sleep peacefully at night”), but it’s not required.

What part of speech is спокойно, and why isn’t it спокойный?