~のだ / ~のです (explanatory)
grammar377 sentences
The sentence-ending のだ (plain) / のです (polite) — and their contractions んだ / んです — framing the preceding clause as an explanation, reason, or fact-being-told. After nouns and な-adjectives, な intervenes (なのだ / なんです). Conveys 'here is the situation,' 'it's that X,' or 'the reason is that X.' Extremely common in everyday Japanese for softening, contextualizing, asking for an explanation, or hedging a request.