This is a short way to say 〜のだ or 〜のです. You use it to explain something. It also gives a reason for what you say.
Clause + んだPrimary
Clause + んです
This is a short way to say 〜のだ or 〜のです. You use it to explain something. It also gives a reason for what you say.
「どうして遅刻したんですか？」「すみません、寝坊したんです。」
"Why were you late?" "I'm sorry, I overslept."
「顔色が悪いね。」「うん、ちょっと頭が痛いんだ。」
"You look pale." "Yeah, I have a bit of a headache."
もう帰るの？悪いけど、これ以上ここにいたくないんだ。
You're going home already? I'm sorry, but I don't want to be here any longer.
田中さんは本当に親切なんです。いつも手伝ってくれます。
Mr. Tanaka is a really kind person. He always helps me out.
彼が犯人なんだという証拠はどこにもない。
There is no evidence anywhere that he is the culprit.
Think of it like a special glue. This glue changes based on what it's sticking to. If you are gluing a verb or an い-adjective, the glue attaches directly. If you are gluing a noun or a な-adjective, you need a small 'な' in the middle of the glue.
This is different from 〜のだ. 〜のだ is for both talking and writing. 〜んだ is mostly for talking. Using 〜のだ when you talk can sound a little stiff.
Watch out: Do not use 〜んだ / 〜んです all the time. Only use it when you explain something. Or when you want to make a strong point. For example, 'The sky is blue' does not need it. Unless you are explaining why something else happened.
Use this when you want to explain something. It shows why something is happening. It gives background information. It helps others understand the situation better.
More formal alternatives(2)
Less formal alternatives(1)
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