modality N4 uncommon writtenpolite

〜ない〜はない — there is no ~ that doesn't ~

〜ない〜はない・ないはない

Builds on ない形

Meaning

there is no ~ that doesn't ~ / every ~ does ~ — a double negative that asserts something holds without a single exception

彼かれが来こない日ひはない。

There's no day he doesn't come. (He comes every single day.)

Attaches to	Form	Example
Verb (ない-form) modifying a noun, then は + ない	V(ない) + N + は + ない	知しらない人ひと + はない → 知しらない人ひとはない

この町まちで彼女かのじょの名前なまえを知しらない人ひとはない。

There's no one in this town who doesn't know her name.

あの頃ころは、努力どりょくしない日ひはなかった。

Back then, there wasn't a single day I didn't put in the effort.

Emphatic and somewhat written/literary; the two negatives cancel into a strong universal ('without exception'). Don't confuse with 〜ないことはない ('it's not that ~ can't,' a hedged partial affirmation) — there the second negative attaches to こと, not a counted noun.

Jengo shows 〜ない〜はない the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.

Sources Compiled from published Japanese grammar references.