I teach an ESL Class for Spanish speakers. I've taught them the rules regarding "double negatives". Today, I had them translate the Spanish equivalent of "It isn't that he doesn't understand me." They pointed out the double negative & I'm not sure how to explain the contradiction. Can someone help?
Double negatives are more complicated than just multiple negatives in a sentence negating each other. That's the case where teachers usually focus their efforts. But there's communication issues beyond that.
It isn't that he doesn't understand me.
has two negatives, but they're not countering each other. We can realize this pretty quickly if we remove both to consider the "straight" meaning.
It is that he understands me.
But it isn't that, either. You're talking about a problem, and in this case, he probably understands you, but that isn't the issue, and it wouldn't be the problem if he didn't understand you. You're concerned about an additional problem that's orthogonal to whether or not he understands you - but it still could be at least somewhat related.
This is technically a fine statement, grammatically speaking. But it is a little difficult to understand because the more negatives you have in a sentence, the harder it is to understand it. It could be better to say something like
Whether or not he understands
Regardless of whether he understands
so that it's more clear. However, that isn't how we commonly talk - I mean, apart from the autistic guy in the virtual room who has literally spent days thinking about this stuff. And that's probably a good thing, because I don't think it was necessarily a good use of my time.