W dzień pracuję w biurze, a w nocy czytam książkę.

In the daytime I work in the office, and at night I read a book.

Breakdown of W dzień pracuję w biurze, a w nocy czytam książkę.

• w: in
• czytać: to read
• książka: the book
• pracować: to work

Questions & Answers about W dzień pracuję w biurze, a w nocy czytam książkę.

Why is it w dzień but w nocy? Why are they different?

Both mean during the day / at night, but they use different cases and slightly different structures:

• w dzień – literally in (the) day, but it works as an adverbial time phrase, similar to during the day.

  • dzień is in the accusative (same form as nominative for this noun).
  • This is a common, idiomatic way to talk about time.

• w nocy – literally in (the) night, also meaning at night.

  • noc in locative is nocy, so this is locative after w.
  • This one is more clearly a preposition + locative time expression.

In everyday speech, both patterns are normal and you just learn them as fixed expressions:

• w dzień – during the day
• w nocy – at night

Could you also say w dniu instead of w dzień?

You can say w dniu, but:

• w dniu is more formal and usually used with a specific date:
  • W dniu 1 stycznia… – On the 1st of January…
• w dzień is the natural, everyday way to say during the day in this general, habitual sense.

So in this sentence, is the normal, idiomatic version. would sound odd if you are talking about your regular routine.