yoru ha soto no oto ga urusai node, mado wo simemasu.

夜は sets night as the topic: as for the night / at night.

In Japanese, は often marks the time or situation being talked about, especially when giving a general statement. So:

• 夜は外の音がうるさい = At night, the outside noises are loud
• It is not necessarily emphasizing one specific night, but talking about nighttime as a general condition.

You could think of 夜は as meaning:

• at night
• during the night
• as for nighttime

夜に and 夜は are not the same.

• 夜に simply marks the time when something happens: at night
• 夜は makes night the topic and often suggests contrast or a general condition: as for nighttime

In this sentence, the speaker is describing what nighttime is like:

• 夜は外の音がうるさい = At night, outside noises are loud

If you said 夜に, it would sound more like you are just placing an event in time, rather than describing nighttime as the topic.

So 夜は is more natural here because the sentence is about a typical nighttime situation.

外の音 literally means the sound of outside or outside sounds/noise.

Breakdown:

• 外 = outside
• の = connects nouns, often like ’s or of
• 音 = sound

So:

• 外の音 = outside sound(s) / noise from outside

Here, の links outside to sound, showing where the sound comes from.

In 外の音がうるさい, が marks 音 as the thing that has the property うるさい.

So the structure is:

• 外の音がうるさい = the outside noise is loud/noisy

Why が?

Because うるさい is describing 音, and が often marks the subject of an adjective or description.

Compare:

• 外の音がうるさい = The outside noise is loud
• 外の音はうるさい = As for the outside noise, it is loud

The second one is possible in some contexts, but it sounds more contrastive or topic-focused. The original sentence is just naturally identifying outside noise as the thing that is noisy, so が is the most natural choice.

It can mean both, depending on context.

うるさい often means:

• noisy
• loud
• annoyingly loud

In this sentence, 外の音がうるさい means the outside noise is not just physically loud, but loud enough to be bothersome. So a natural English idea is:

• The noise outside is loud
• The noise from outside is noisy/annoying

Because the speaker then says they close the window, the nuance is probably annoyingly noisy.

Because うるさい is an い-adjective, and before ので you use the adjective in its plain form:

• うるさいので = because it is noisy

You do not use the -く form before ので.

Compare:

• うるさいので = correct
• うるさくので = incorrect

The -く form is used in other patterns, such as:

• うるさくて = it’s noisy, and...
• うるさくない = not noisy

But with ので, use the plain form:

• 寒いので
• 高いので
• うるさいので

Both can mean because, but they have slightly different nuances.

• ので sounds a bit more neutral, explanatory, or softer
• から sounds more direct and assertive

So:

• 外の音がうるさいので、窓を閉めます。 = Because the outside noise is loud, I close the window.

This sounds like a calm explanation.

If you used から:

• 外の音がうるさいから、窓を閉めます。

That is also natural, but slightly more direct: I’m closing the window because it’s noisy outside.

In many everyday situations, both work. Here, ので gives a polite, explanatory tone.

This is very common in Japanese.

Before ので, you use the plain form:

• うるさいので

But the main sentence can still end politely:

• 窓を閉めます

So the sentence mixes:

• plain form before a grammar connector
• polite form at the end

This is completely normal.

A similar example:

• 時間がないので、急ぎます。
• Because I don’t have time, I’ll hurry.

You do not need to make うるさい into うるさいですので here. The plain form before ので is standard.

The subject is omitted because Japanese often leaves out things that are understood from context.

So:

• 窓を閉めます literally = (someone) closes the window
• In natural context, it usually means I close the window or I will close the window

Since this sounds like the speaker explaining their own action, the natural interpretation is:

• I close the window because the noise outside is loud at night.

Japanese often omits I, you, we, and so on when they are obvious.

を marks the direct object of the verb.

Here:

• 窓 = window
• 閉めます = close
• 窓を閉めます = close the window

So 窓 is the thing being closed, which is why it takes を.

Yes, though they are related.

• 閉める / 閉めます is commonly used for closing something like:
  • windows
  • doors
  • shops
  • eyes
• 閉じる / 閉じます often means to close something too, but it can also mean to shut or to close up, and it is often used with things like:
  • books
  • lids
  • eyes
  • accounts
  • opportunities

For a window, 窓を閉めます is the most natural everyday choice.

The sentence breaks down like this:

• 夜は = as for nighttime / at night
• 外の音が = the outside noise
• うるさいので = because it is noisy
• 窓を閉めます = I close the window

So the overall structure is:

[time/topic] + [reason] + ので + [main action]

More literally:

As for nighttime, because the outside noise is loud, I close the window.

More natural English:

At night, because the noise outside is loud, I close the window.

Yes.

閉めます can mean:

• close
• will close
• sometimes am closing

Japanese non-past forms often cover both present and future, depending on context.

So this sentence could mean:

• I close the window because the outside noise is loud at night.
• I will close the window because the outside noise is loud at night.

If the speaker is talking about a habitual action, it means I close the window. If the speaker is talking about what they are about to do now, it can mean I’ll close the window.