～ない～はない is an example of a double negative in Japanese, and is a grammar construction that requires careful attention in order not to incorrectly interpret. Both the 形容詞（けいようし） (
い-Adjective), and 助動詞（じょどうし） (Auxiliary verb) forms of ない may be used in this construction, depending on what type of word is being negated. Let’s take a look at a few examples.
-
彼（かれ）にはピアノで弾（ひ）けない曲（きょく）ない。
There is no song that he can't play on the piano.
-
私（わたし）は美味（おい）しくない食（た）べ物（もの）は食（た）べない。
I don't eat food that does not taste good.
-
彼（かれ）は安（やす）くない靴（くつ）は買（か）わない。
He doesn't buy shoes that aren't cheap.
Literally, this grammar pattern is very similar to ‘there isn’t an (A) that doesn’t (B)’ in English.
This term is not to to be confused with
なくはない, a more advanced grammar pattern which means ‘It’s not that it isn’t (A)’.
-
私（わたし）に書（か）け
ない漢字（かんじ）はない。
There is no kanji that I cannot write.
-
私（わたし）は漢字（かんじ）を書（か）けなくはないけど...
It's not that I can't write kanji, but…