N3 Reasons, Causes, and Results

~(んだ)もの/もん: meaning, usage and examples

~(んだ)もの/もん means: because... (informal, often for excuses).

Updated 9 November 2026 · By the My Senpai team · Spotted a mistake? Tell us

Examples

1. 「どうして宿題しゅくだいしなかったの?」「だって、時間じかんなかったんだもん。」

   "Why didn't you do your homework?" "Because I didn't have time."

2. 「また食たべたの？」「だってお腹なかが空すいてたんだもの。」

   "You ate again?" "Because I was hungry!"

3. 「もう帰かえるの？」「だって、つまらないんだもん。」

   "Leaving already?" "Well, it's boring!"

4. 「野菜やさいも食たべなさい。」「だって、きらいなんだもん。」

   "Eat your vegetables too." "But I don't like them!"

When to use it

Used at the end of a sentence to give a personal reason, usually as an excuse or to justify yourself: "but..." or "because...". It often follows だって ("but"): 「どうして食たべないの？」「だって、まずいんだもん」. Children, close friends, and family members use it in casual conversation.

Nuance

Very casual and a little childish or sulky. もん is more casual than もの. Children use it most, and adults use it with close friends and family. Never use it at work or with people above you.

Compare

から and ので simply give a reason and work in any setting. んだもん adds personal feeling and self-justification: 行いきたくないから is neutral, while 行いきたくないんだもん sounds like pouting. Do not confuse it with ものだ (a general truth or a nostalgic memory).

Tip: Remember the pair だって ... もん: "But... it is because..." It almost always answers a question or a complaint.