nakunai なくない

In Japanese, nakunai なくない means "is not not" or "there is not no" or "[I] don't have no." It's a double negative, so it translates to the positives "is," "there is," and "[I] have."

Grammatically, it'a the i-adjective or negative auxiliary nai ない, inflected to the adverbial form, naku なく, plus the negative auxiliary nai ない. So it's nai twice.

• Grammar
• Usage
  
  • なくなくない
• 無くない

Grammar

The negative auxiliary nai ない is used to create the negative form of verbs and adjectives.

• kawaii
  可愛い
  Is cute. (i-adjective.)
• kawaikunai
  可愛くない
  Is not cute.
• wakaru
  分かる
  To understand. (godan verb with ru ending.)
• wakaranai
  分からない
  To not understand.

So the negative form of the words above end in nai ない. The problem is, this nai ない can be inflected like an i-adjective. So you can inflect the nai ない to its own negative form:

• ~nai
  ～ない
  Is not. (suffix that works like an i-adjective.)
• ~nakunai
  ～なくない
  Is not not. (negative form of suffix that works like an i-adjective.)

That means you can say this:

• kawaiku-nai
  可愛くない
  Is not cute.
• kawaiku-naku-nai
  可愛くなくない
  Is not not cute.
  Is cute.
• wakara-nai
  分からない
  Is not to understand.
  To not understand.
• wakara-naku-nai
  分からなくない
  Is not not to understand.
  To not not understand.
  Is to understand.
  To understand.

Usage

Logically, there's no logical reason to say "is not not cute" if you can just say "is cute." But that doesn't mean people don't so that.

One way nakunai is used is instead of janai for agreement. For example:

• ii-n-janai?
  いいんじゃない？
  Isn't [it] good?

The phrase above translates literally to "[it] isn't good?" When people say that, they're in practice saying: that's good, isn't it? Isn't that good?

In other words, they want to know if it "is good," but they ask whether it "is not good."

Similarly:

• yokunai
  よくない
  Is not good.
  • ii いい and yoi よい are synonyms meaning "good." But normally ii いい is used to say just "good," and yoi is used for every other inflection, like "not good."
• yokunakunai?
  よくなくない？
  Is not not good?
  • Isn't [that] not good?
  • Is [that] good?

Another example:

• sugoi janai?
  すごいじゃない？
  Isn't [that] incredible?
• sugoi jan?
  すごいじゃん
  (same meaning.)
• sugokunakunai?
  すごくなくない？
  (also same meaning.)

A less normal case is when two characters go back-and-forth trying to deny what the other is saying by just adding a nai at the end of the sentence.

• kawaii!
  可愛い！
  [It] is cute!
• kawaikunai
  可愛くない
  (you're wrong.) [It] is not cute.
• kawaikunakunai
  可愛くなくない
  (no u.) [It] is not not cute.

なくなくない

The phrases nakunakunai なくなくない, nakunakunakunai なくなくなくない, nakunakunakunakunai なくなくなくなくない, and so on, are just evolved forms of nakunai with triple, quadruple, quintuple negatives and beyond. For reference:

1. nai
   ない
   Is not.
2. naku-nai
   なくない
   Is not not.
   Is.
3. naku-naku-nai
   なくなくない
   Is not not not.
   Is not.
4. naku-naku-naku-nai
   なくなくなくない
   Is not not not not.
   Is not not.
   Is.
5. naku-naku-naku-naku-nai
   なくなくなくなくない
   Is not not not not not..
   Is not not not.
   Is not.

Of course nobody is ever going to say this under normal situations, but, grammatically, it's still all correct.

無くない

Sometimes, nakunai 無くない is a normal adjective inflected to negative form instead of the negative auxiliary inflected to negative form. In this case, the grammar is the same, except it's the antonym of aru ある.

• jikan ga nai
  時間が無い
  Time is nonexistent.
  There's no time.
  We're out of time. We're going to be late. We won't make it. Etc.
• jikan ga nakunai?
  時間が無くない？
  Time is not nonexistent?
  Isn't time nonexistent?
  Isn't there no time?
  Aren't we out of time? Aren't we going to be late? Etc.

Some examples with the null particle:

• kankei nakunai?
  関係なくない？
  Relationship is not nonexistent?
  Isn't that unrelated?
  Doesn't that have nothing to do with it?
• yaru koto nakunai?
  やることなくない？
  Isn't there nothing to do?
  • See ~koto nai ～ことない.