Yeah, the change of meaning is often very subtle, and people can sometimes disagree on the direction of the change.

Usually though, the device is used to express a kind of understatement. Compare these statements:

He's not bad looking

He's good looking

Which one would you say is stronger? I think most people would say that the affirmative "He's good looking" is stronger than the first version. Another example:

It's not without flaws

It's flawed

If you say "not without flaws", you're usually saying something like "it's good despite its flaws", so that version understates the case compared to the other one.

Again, though: my point was mostly that the meanings are distinct and that language is not mathematics. You can't just replace two minus signs with a positive one and expect the to get the same thing on the other side. Nor should you follow any simple "rule" like that blindly.

I don't think that authors you mentioned would have bothered using this as a creative flourish if it was just meant to be interpreted in an extremely literal way. The whole fact that they bothered means that there's some alternative meaning, whether the slightly sarcastic one I understand or something else.

"Which one would you say is stronger?"

I would go for "He's not bad looking" being stronger - but then again I'm from the UK :-)

"It's not without issues" to me means I might object to parts of it but overall I'm positive, or I feel the issues can be accommodated, tolerated, or corrected.

"It has issues" is to me a stronger, more general objection to the whole thing.

Your username implies that you're from the UK. Isn't this a well-known cultural difference between British and... just about any other culture? I know we Dutch people get caught by that quite often.

(Funny enough, in the Groningen region the expression "kon minder" ("could be worse") is often used as high praise. Whatever it applies to is implied to be fantastic, almost perfect, in a "but don't get cocky about it" kind of way)

You're right. Actually, I remember a story [1] of a British army commander asking his American superior (on a UN mission) for help by saying "Things are a bit sticky, sir". Unfortunately this was taken to mean that everything was fine, so no reinforcements were sent.

I understand that the Dutch are very much at the other end of the spectrum - very direct and straightforward.

[1] https://www.theguardian.com/uk/2001/apr/14/johnezard

Honestly, after living abroad for five years in total (with one year back in the Netherlands inbetween), that "direct and straightforward" part feels like it has been co-opted as an excuse to not bother with looking at things from the point of view of someone else and reaching out.

> Isn't this a well-known cultural difference between British and... just about any other culture?

At least in French, litotes are meant to amplify the negative.

The classical example being in Le Cid, "Go, I don't hate you" from Chimène to Rodrigue (who just killed her father), meaning "I love you".

Other example can be found, "Not OK" meaning totally unacceptable, "Not bad" meaning excellent, or "Not stupid" meaning very clever. Of course, all litotes can be interpreted literally, and you often need context or tone to convey the meaning