Translation guide
In Japanese, expressing 'accidentally' depends on whether the action was unintentional, a mistake, or something that happened by chance. The most common way is using the verb ending 〜てしまう, which conveys that something happened unintentionally or regrettably. Other expressions like うっかり, 偶然, and 間違って are used for specific nuances.
Express that an action was done without intention, often with a sense of regret or unexpectedness.
Attach to the te-form of a verb to indicate that the action was done unintentionally or completely, often with a nuance of regret. 〜ちゃう is the casual contraction.
ケーキを全部食べてしまった。
I accidentally ate all the cake.
I accidentally forgot my wallet.
An adverb meaning 'carelessly' or 'absentmindedly'. Used when the accident is due to inattention or forgetfulness.
うっかり電車を乗り過ごした。
I accidentally missed my stop.
うっかり彼の名前を忘れてしまった。
I accidentally forgot his name.
An adverb meaning 'without thinking' or 'in spite of oneself'. Often used for actions done out of habit or impulse.
つい食べ過ぎてしまった。
I accidentally ate too much.
つい秘密を話してしまった。
I accidentally told the secret.
Express that an action was done incorrectly or by error.
The te-form of 間違う (to make a mistake), used adverbially to mean 'by mistake' or 'erroneously'.
間違って彼の傘を持って行ってしまった。
I accidentally took his umbrella by mistake.
間違ってメールを消してしまった。
I accidentally deleted the email.
A more formal version of 間違って, often used in written or official contexts.
誤って個人情報を送信してしまいました。
I accidentally sent personal information.
Express that something happened by chance, without planning.
An adverb or na-adjective meaning 'by chance' or 'coincidentally'. Used for unexpected but not necessarily negative events.
偶然彼に会った。
I met him accidentally (by chance).
偶然その本を見つけた。
I accidentally found that book.
A casual adverb meaning 'by chance' or 'coincidentally'. Similar to 偶然 but more conversational.
Express that an action was made to look accidental but was actually intentional.
An adverb meaning 'in a contrived manner' or 'as if on purpose'. Used when someone pretends something was an accident.
彼はわざとらしくコップを倒した。
He knocked over the cup accidentally on purpose.
〜てしまう is a grammatical construction that attaches to verbs and can express unintentional actions in general. うっかり is an adverb specifically for careless mistakes due to inattention. You can combine them: うっかり忘れてしまった (I carelessly forgot).
うっかり忘れてしまった。
I accidentally forgot (carelessly).
偶然 implies a chance occurrence, not a mistake. If you delete a file by mistake, use 間違って or 〜てしまう, not 偶然.
たまたま通りかかった。
I happened to pass by.