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My wife and I communicate in English. She's Japanese, I'm Norwegian and we're both language enthusiasts; this makes for a lot of interesting language discussions.
This is something that surfaced today:
"Is this not so good anymore?", says my wife, holding up an old container of barbecue sauce which she thinks has gone bad. "Yes", I answer, meaning that the sauce has gone bad.
Disregarding that a) the question could probably have been formulated in a different way to make it less ambiguous and b) I could have been more verbose in my answer; would answering "Yes" or "No" to this question, in English, indicate that the sauce has, indeed, expired?
Both of our native languages handle these kinds of "negative questions" a bit differently and we can't seem to figure it out in English.