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verb-conjugated-as-an-adjective)

言わない (negative)

言わなく・ない (negative+negative)

言わなく・なかった (negative+negative+past)

I've never seen this conjugation before. Why would you have a negative +
negative? Where is that coming from? How does that work exactly?
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2013-04-20T11:30:57.820
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2013-04-22T12:02:16.677
2017-04-13T12:43:44.207
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verbs tense subsidiary-verbs
What is なく・ない and why is it used?
Double negatives are used not just in Japanese.

> It's not that I'm not hungry...

Since (-1)•(-1)=1, it makes only sense to use a double negative, if its
meaning is different from the positive, viz. either stronger or weaker than
the positive.

In English, the double negative feels weaker than the positive. In Japanese,
the double negative is stronger than the positive. Maybe because negation is
in general felt to be quite strong. (To me) it makes sense, then, that double
negation would be stronger than no negation.

I don't think double negation is used often to give a strong positive
statement. But the negative question, like

> お茶を飲みに行かない？

is likewise applied to negative forms, e.g.

> あまりおいしくなくない？  
>  Don't you (also) think it's not very good?

Of course the idea of negating a negative can be extended ad infinitum, like
in the phrase これよくない？よくないこれ？よくなくなくなくなくせいいぇい
([YouTube](http://www.youtube.com/watch?feature=player_detailpage&v=HSQNaXBjA5c#t=130s)).

Caveat: Sometimes the double negative can have the same meaning as the
negative. E.g.

> よくない？

asks whether something is good. Then the answer

> よくなくない。

can mean "not good".

I guess the better strategy is to rely on other factors than the number of
negations...
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2013-04-20T12:40:22.147
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2013-04-20T12:54:13.780
2013-04-20T12:54:13.780
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In addition to the previous answer, often these forms are seen with an
particle in the middle (は or も), and are used followed by for such as が・けど
(examples borrowed/stolen from internet, any translation mistakes my own)

気持ち分からなくはないけど... It's not that I don't understand his feelings, but... (I
**do** understand, but I still don't approve of his actions/won't change my
mind/etc)

まあ、言わなくもないけど… 時と場合によるよ... Well, it's not that I wouldn't say that... it
depends on the situation... (I **would** say that... but maybe not at this
time/in this case)
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answer