What it means
だって introduces a reason or justification, often translated as “because” or “after all.” It commonly appears at the beginning of a spoken sentence or clause when the speaker is defending a decision, explaining a situation, or responding to an objection. It has a conversational, emotionally expressive tone and often presents information that the speaker believes should make the reason obvious.
Usage note
だって is strongly associated with familiar spoken language and does not have a simple polite counterpart with exactly the same nuance. In formal writing or careful speech, use a more neutral expression such as なぜなら or というのも instead.
Example sentences
今日は自転車で行かないよ。だって、午後から雨が降るそうだから。
I’m not going by bicycle today. Because they say it will rain from this afternoon.
今日は図書館で勉強することにした。だって、家では弟がゲームをしていて集中できないから。
I decided to study at the library today. Because my younger brother is playing video games at home, I cannot concentrate.
その店では買