Grammar › Nuance › 〜んです

Grammar · explanatory ん

〜んです

The "explanatory" ん. It doesn't change what you say — it frames it as background, a reason, or the very thing that needs explaining.

The short version

Take the plain form of a verb or adjective and add んです. Nothing about the fact changes — you're signalling "here's the situation / the reason / the point". Casual talk shrinks it to んだ or just の; formal writing spells it out as のです.

疲つかれた → 疲つかれたんです — I'm tired (…that's what's going on)
casual 疲つかれたんだ／の ・ formal 疲つかれたのです — same ん, different register

んです frames a "you see / that's why"

Attached to a plain statement, ん presents it as explanation — the backstory behind what you (or the other person) just saw or asked. It's how a plain report turns into "the thing is…".

Actually, there are four of them, you see. (presenting the fact as explanation)
▶ Nihongo con Teppei 波! · #11 トイレの話 · 2:37 — hear it →

なんです — after nouns & な-adjectives

After a noun or a な-adjective, you need な before the ん: 学生がくせいなんです ("(the thing is) I'm a student"), 好すきなんです. The everyday agreement そう ("that's so") becomes そうなんです.

Yes, that's exactly it. (そう + な + んです — confirming with the "explanatory" ん)
▶ カフェラジオ · Ep.29 · 7:44 — hear it →

Watch out

🗣 〜んだけど sets something up. In casual speech you'll constantly hear んだ, and 〜んだけど as a soft lead-in — "so, here's the deal, and…". It often trails off, leaving the request or complaint unsaid.
I'm honestly wiped out, though… (んだ + けど — framing a complaint)
▶ Haru no Nihongo · EP-320 · 14:34 — hear it →
Don't sprinkle it on everything. Plain 疲つかれた just reports "I'm tired". 疲れたんです explains — "(that's) why I'm quiet / why I want to go home". Use ん when there's a reason or context in the air; drop it for a flat statement of fact. のです is the stiff written form — great in essays, a bit formal out loud.
Hear 〜んです in real Japanese
Free · tap any word for its reading & meaning
Open in Wakatta

Next: だろう・でしょう — probably / right? → · ね・よ・なあ → · All grammar

Free on Wakatta — learn Japanese by listening. Every example above is a real line from a Japanese podcast, timestamped so you can hear it.