んですndesu“to explain or emphasize”

んです is an ending you add to a sentence when it explains something: the reason behind a situation, the background to what is happening, or the answer to an unspoken “why?”. It is a JLPT N5 pattern, and it is one of the clearest signs of natural spoken Japanese.

If you arrive late and say 電車が遅れました, you are just reporting a fact. If you say 電車が遅れたんです, you are explaining: “The train was delayed, you see.” English has no single word for this, so translations like “the thing is,” “you see,” or “it’s that…” are only approximations.

んです connects your sentence to the situation: “here’s the background you need.”

What does んです mean?

んです is a contracted form of のです. The の turns the sentence into “the fact that…”, and です states it politely: “it’s (the case) that…”. In speech の almost always shrinks to ん.

It has three core jobs:

• Explaining: giving a reason or background, often for something the listener has noticed or is about to ask. 頭が痛いんです — “I have a headache (that’s why).”
• Asking for an explanation: 〜んですか asks about something you have seen or heard. どうしたんですか — “What happened? / What’s wrong?”
• Setting up a request: 〜んですが… gives background before asking a favour. 道がわからないんですが… — “I don’t know the way…”

How to form んです

んです attaches to the plain form. Verbs and い-adjectives connect directly. Nouns and な-adjectives need な in the present tense.

The question form is んですか. In casual speech, use んだ for statements and の？ for questions: 忙しいんだ (“I’m busy, see”), どうしたの？ (“What’s wrong?”).

When is んです used?

• Excuses and apologies: すみません、寝坊したんです。 — Sorry, I overslept.
• Declining an invitation: 今日はちょっと…用事があるんです。 — Today’s a bit… I have something on.
• Reacting to what you notice: you see a friend with a big suitcase — 旅行に行くんですか。 “Are you going on a trip?”
• Explaining a compliment or surprise: someone praises your Japanese — 母が日本人なんです。 “My mother is Japanese.”
• Before a request: 写真を撮りたいんですが… — “I’d like to take a photo…” (could you help?).

It is conversational. In essays and formal writing you will see のです instead, and in neutral reporting you will see plain です/ます.

んです example sentences

In examples 1 and 2 the んです sentence comes second. First you state what is happening, then you give the reason with んです. That order is very common.

Nuance of んです

んです assumes shared context. When you ask 〜んですか, you are showing that you have noticed something and want to understand it. That makes the question sound engaged and warm, which is why どうしたんですか is far more natural than どうしましたか between friends and colleagues.

The same feature can backfire. Asking a stranger 何歳なんですか (“So how old are you?”) sounds nosy, because it suggests you have been wondering about it. And a string of statements all ending in んです sounds like you are constantly justifying yourself. Use it when there really is something to explain.

💡 Trailing off: 〜んですが… or 〜んですけど… left unfinished is a polite way to hint at a request. The listener fills in “can you help?” — you don’t have to say it.

んです vs です

Both are polite endings, and both can end the same sentence. The difference is whether you are stating or explaining.

A teacher announcing the schedule says 明日、試験があります. A student turning down an invitation says 明日、試験があるんです. For more on the plain です/ます endings, see だ / です, and for the full form behind ん, see のです.

Common mistakes with んです

Is んです on the JLPT?

In listening tasks that ask “Why can’t the woman come?”, the answer is very often the sentence that ends in んです. Train your ear to catch it.

Practice questions for んです

Learning path for んです

Related grammar to review next

• のです — the uncontracted, more written form of んです with the same meaning.
• どうして — the “why?” question that is usually paired with んですか.
• ので — gives a reason inside one sentence, while んです gives it as a separate explanation; both use なので/なんです after nouns.
• から — another way to state a reason; 〜からです and 〜んです often answer the same question.

Learn んです with Hane

Hane practises んです in short dialogues, so you learn to hear it as “here’s the reason” and use なんです without thinking. Try it in Hane.