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I encountered a couple of sentences, mostly in American movies, that I wondered why they have something I call ' Double negatives', for example:
Don't go no further (why not Don't go further)
We can't grow no crops without no water
I don't see no friends (why not I don't see any friends / I see no friends)
What's the structure of these sentences, are these considered informal? Are there any other correct alternatives to them?