Learn Hardcore Japanese: yoru ni ongaku wo kikimasu.

In Japanese, に marks a specific point in time when an action occurs. Here, 夜に means “at night.” Without に, 夜 would be treated more like a topic or contrast rather than simply indicating when you listen to music.

Can you omit に after 夜, and if so, how does the meaning change?

Yes. You could say 夜音楽を聞きます or more naturally 夜は音楽を聞きます.

夜音楽を聞きます feels informal and might sound clipped.
夜は音楽を聞きます uses は to set “night” as the topic (“As for night, I listen to music”), implying a habitual action at night.

Why is there no subject in 夜に音楽を聞きます?

Japanese often omits the subject (like “I,” “you,” “he,” etc.) when it’s clear from context. Here, it’s understood the speaker is talking about themselves: “(I) listen to music at night.”

Why is を used after 音楽 instead of another particle?

を marks the direct object of a transitive verb. Since 聞く (to listen) acts on 音楽 (music), you attach を: 音楽を聞きます (“listen to music”).

Why is the verb 聞きます placed at the end of the sentence?

Japanese follows a Subject–Object–Verb (SOV) word order. Time phrases like 夜に and objects like 音楽を come before the verb, which always concludes the clause.

What’s the difference between 聞く (kiku) and 聴く (kiku), and which one applies here?

Both read kiku, but:

聞く generally means “hear,” “ask,” or “listen to” in everyday use.
聴く emphasizes attentive listening (e.g., concerts, music appreciation).
In normal writing and speech, 聞く is standard for “listen to music.”

Does 夜に音楽を聞きます imply a habitual action or one-time event?

In the -ます form, it usually indicates a routine or habit: “I listen to music at night (regularly).” For a one-time action, you might specify context or use the past tense: 昨夜音楽を聞きました (“Last night I listened to music”).