Is 必要なくない the same as 必要なくはない?

I know that なくはない is a double negative and it means "It's not that... [sth
isn't]..." However, I asked my Japanese language partner about the difference
and she can't explain it well, but she says that they are different. I'm
confused because I can't find any entry on なくない.
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2021-03-27T07:01:38.390
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2021-03-27T10:49:36.460
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question
grammar
Is 必要なくない the same as 必要なくはない?
The difference is the same as that between 赤くない and 赤くはない, etc. As far as this
は is concerned, there is nothing specific to double negation. は in a negative
sentence can be an explicit contrast marker, but sometimes it's nothing more
than a particle you use unconditionally in negative sentences.

  * [Why is the topic marker often used in negative statements (ではない, ～とは思わない)?](https://japanese.stackexchange.com/q/1077/5010)

> So how did the は come to be used anywhere? This is probably part of an
> historical process of trivialization and loss of meaning. It seems to me
> that originally, the pattern ～ではない was used to only mark a strong contrast
> of the entire predication to something else (e.g. something that was said or
> implied before by someone else), but later became more and more popularized
> until what originally was a contrast marker became an almost necessary
> feature of the negative form.

は in 必要なくはない _can_ carry a strong contrastive meaning (similarly to 必要ではある
which is always strongly contrastive).

> 値段はとても高いが、必要なくはない。  
>  It's very expensive, but it doesn't mean it's unnecessary.  
>  (は is mandatory here)
>
> 値段はとても高いが、必要ではある。  
>  It's very expensive, but it _is_ necessary.

When this contrastive meaning seems unimportant, you can think it's just a
common and natural way to say "It's not unnecessary". In such cases, it's
basically interchangeable with 必要なくない. Still, 必要なくない sounds colloquial, and
you should use 必要なくはない in formal settings. I suppose most textbooks use なくはない
almost unconditionally.
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2021-03-27T10:36:24.517
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answer