Learn Hardcore Japanese: kinou ha densya no oto ga ookikatta node, watasi ha mimi wo husagimasita. - Because the train noise was loud yesterday, I covered my ears.

In Japanese, は can mark the topic of the sentence, not just the subject. By saying 昨日は, you’re setting “yesterday” as the topic—“As for yesterday,…” This is more common in everyday speech when you want to comment on the conditions or events of that time. You could say 昨日に to mean “on yesterday,” but that’s more formal/time‐specific and less about making yesterday the topic.

What role does の play in 電車の音?

The particle の connects two nouns to show a relationship—often possession or attribution. In 電車の音, it literally means “the sound of the train.” Here, 電車 attributes what kind of sound you’re talking about. Think of it like the genitive (‘of’) in English.

Why is が used after 音 instead of は?

After 音, が marks the subject in the subordinate clause 電車の音が大きかったので. You’re simply stating a fact there (“the train’s sound was loud”), so you use が for a new or focusing subject. If you used は, it would imply contrast or already-known info.

How does 大きかった relate to the adjective 大きい?

大きい is an い-adjective in present tense (“is big”). To put it in past tense, you replace the final い with かった, giving 大きかった, which means “was big.” That’s why 大きかった expresses that the sound was loud/big.

What exactly does ので do in 大きかったので?

ので is a conjunction meaning “because” or “since,” giving a reason with a slightly softer, more explanatory tone than から. Here 大きかったので means “because it was loud.” It links the cause (loud sound) to the effect (covering your ears).

Why is 私は stated again before 耳をふさぎました? Can it be omitted?

Japanese often drops the subject when it’s clear. 私 is repeated with は mainly for clarity or emphasis (“As for me, I…”) especially in longer sentences or polite contexts. You could omit 私は and say 耳をふさぎました, and it would still be natural if the listener knows you’re the one acting.

What does 耳をふさぎました mean, and why is を used after 耳?

耳をふさぎました literally means “(I) covered/blocked (my) ears.” The verb ふさぐ takes a direct object (the thing being blocked), so を marks 耳 as that object. In context, it means you plugged or covered your ears because the noise was too loud.

Why is the verb in polite form ふさぎました instead of the plain past ふさいだ?

Japanese has levels of politeness. ふさぎました is the polite past form, suitable for formal situations or when you want to be courteous. The plain past ふさいだ is more casual and used among friends or in writing/dialogue that’s informal.

Could you swap the order of the clauses, like 電車の音が大きかったので昨日は耳をふさぎました?

Yes, you can rearrange clauses in Japanese more freely than in English. 電車の音が大きかったので昨日は耳をふさぎました is grammatically fine, but starting with 昨日は highlights the time-topic first. Changing the order may subtly shift what you emphasize (time vs. reason).