～なくはない / なくもない/ないでもない

About

The ～なく(も・は)ない patterns form a double negative that is used to express that "X is not not Y".

These double negative statements are often used to add nuance to a statement that would not otherwise be there with a simple positive statement.

「～なく(も・は)ない」 and 「～ないでもない」 are all possible, with は adding additional emphasis on 「ない」, compared to も.

E.g. ビールは飲のまないでもないけど、あまり好すきじゃない。 "It's not that I don't drink beer, but I don't really like it."

E.g. あのドラマはつまらなくはないけど、特別とくべつ面白おもしろいってわけでもなかった。 "It's not that that drama was boring, but it wasn't particularly entertaining either."

E.g. 有名ゆうめいでなくはないけど、この地域ちいきではあまり知しられてない。 "It's not that it isn't famous, but it's not very well known in this area."

These patterns are primarily used in casual/polite spoken contexts.

Summary

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  The ～なく(も・は)ない patterns are used to express that "X is not not Y"

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  The「～なく(も・は)ない」 and 「～ないでもない」 are also possible