Have you ever noticed how languages and logic seem to be related (negative statements etc), for example English logic is different from Spanish logic? Does that make sense? Can you recommend anything about this topic? Happy conlanging :)
The logic of English and Spanish is not different. Not in the way you're thinking.
You don't make it super clear, but I think you're talking about negative concord. Specifically an example like this in Spanish:
No he visto nada not have.1S see nothing
Being interpreted as "I haven't seen anything." First of all, exactly the same thing is possible in English:
I ain't seen nothing.
If you first interpret the above sentence as "I saw something" with the negatives cancelling, you have either retrained yourself too hard for an English teacher or you are trolling. It's a perfectly normal English sentence that unfortunately is looked down on because some people who fundamentally misunderstood the phenomenon decided to make it everyone else's problem.
Now, it is possible for the “two negatives make a positive” to occur. Take the sentence below:
Sue doesn’t think that Jon won’t go.
The only reading of that is that Sue thinks Jon will go — or she at least thinks he’s likely to go. And you’d get the same reading from the Spanish equivalent, Sue no piensa que Jon no va a ir.
The difference is that in Sue doesn’t think Jon won’t go has a clause embedded in another clause, both of them negated. So the negation of Sue doesn’t think… gets applied to Jon won’t go, which is already negative, so it gets flipped back to positive.
People don’t tend to use those true double negatives because they’re hard to parse. You most likely see them when there’s some pragmatic reason to use it, but that’s another can of worms.
Now, I ain’t seen nothing is not like that. It’s just a simple sentence. What is the logic? Well, there’s just one negation.
This phenomenon is called Negative Concord or Negative Agreement. The verb is negated, and then other parts of the sentence (like the pronoun nothing) agree with that negation. Now, in Spanish, this is totally obligatory: negating the verb requires you to use some negative nouns and pronouns. English has an alternative: I ain’t seen anything,* (or I haven’t seen anything) and some people think this is the only way.
It’s possible in English to also force the negative cancelling by stressing a negated noun/pronoun (I ain’t seen nothing), but the default reading is the negative concord reading for most speakers.
It is also possible to have a language that doesn’t allow negative concord at all. The only example I can think of off the top of my head is Mandarin, and the thing is Mandarin just doesn’t negate nouns or pronouns at all, so maybe someone out there has a better example.
* Weirdly there’s a bit of negative concord-ish behavior still. The use of anything is triggered by a negative here, and you can’t say *I ain’t seen something or *I haven’t seen something.
