GrammarJLPT N5
→ it is assuredly that ...
Explanatory Emphasis: "It is that…" / "The thing is…"
JLPT N5Auxiliary verbNeutral
なんです is the polite spoken contraction of なのです, which itself is the polite form of なのだ. It belongs to the broader explanatory のだ／んだ family and is used to provide an explanation, give background context, assert a reason, or state something with a sense of conviction and assurance. While のです and んです attach directly after verbs and い-adjectives in their plain forms, なんです is the form that appears after nouns and な-adjectives, because the copula だ changes to な before の. In conversation, なんです signals that the speaker is not merely stating a fact but is emphasizing it as an explanation or asserting it with confidence — "the fact is…" or "it is assuredly that…". Compared to a plain statement like 学生です ("I am a student"), saying <strong>学生なんです</strong> adds the nuance of "the thing is, I'm a student" or "I am indeed a student," often implying the listener should understand a situation in light of this fact. In casual speech the polite なんです becomes なんだ. This grammar point is extremely common in everyday Japanese and mastering it is essential for natural-sounding conversation.
Functions
#1 Providing an explanation or reason
Structure
Noun / な-Adjective + なんです
今日は休みなんです。だから、家にいます。
Here なんです attaches to the noun 休み to explain why the speaker is at home. Rather than simply stating 「休みです」 as a neutral fact, adding なんです frames the sentence as background explanation — "the reason is that it's a day off." This is one of the most common uses of なんです: providing context or justification for a situation the listener might be curious about.The thing is, today is a day off. So I'm staying home.
Structures
- Noun
- Noun + なんです
- な-Adjective
- な-Adjective (stem) + なんです
Common mistakes
A very common mistake is using だんです instead of なんです after nouns and な-adjectives; the copula だ must change to な before の／ん, so 「学生だんです」 is incorrect — the correct form is 「学生なんです」. Another frequent error is confusing when to use なんです versus んです: remember that なんです is specifically for nouns and な-adjectives, while verbs and い-adjectives use んです directly after their plain forms (e.g., 「食べるんです」, 「高いんです」). Learners also sometimes overuse なんです in every sentence, but it should only be used when there is a reason to explain, emphasize, or seek explanation — using it in neutral, matter-of-fact statements can sound unnatural or overly dramatic. Finally, some learners forget that in casual speech, なんです becomes なんだ (not なです), and mixing politeness levels within one conversation can sound awkward.
Related
のですんですなのですのだんだからです