I believe it is responding with understated incredulity to something that seemed to imply that the person did not go.

Did you not do X.

Like, did you not hear me when I said.

Which translates to 'what the heck, why weren't you listening, but I htink you were and so I think you are just trying to irritate me or not take responsibility....'

It's not a logical binary to 'did you do X'

It carries extra verbal messages.

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Honourable contributors, pls do not take offense when I say that my OP was addressed to UK English speakers. It is widely understood that US English usage can differ widely from our own meanings in the UK. The English language has been described as the most difficult language in the World. It can take 20 years to become fluent from a constant educated immersion from say age 4 supported by a reading list of some 100 books from classical literature Victorian to modern.

For example Tim's response above I believe shows how the meaning of aspoken sentence can change depending on which word is emphasised.

"Have you stopped beating your wife,"

Try putting stress on each of the six words in turn

Indeed if your really want to get screwed up, try stressing 2 out of 6 , 3 oo 6 , 4 oo 6

Anyone understand or not understand my question :-{}

"Did you or did you not go to the market yesterday" — Robint

"I am a good player, if not the best" — Robint

You are correct in identifying these two constructions as ambiguous. "Did you go to the market yesterday?" is clear. The 'rhetorical' purpose of the first statement's construction is to bear down on the witness [or the husband, the wife, the maid, the child...] with imperious phrasing.

The second statement isn't a good example, as written. I would expect to hear "I am an excellent player, if not the best." There is too large a gap between "good player" and "the best". In any case, the speaker is leaving himself a little space to maneuver. He wants to boast, but isn't quite bold enough to claim the top spot. Mohammed Ali (the boxer) was bold enough; he proclaimed "I am the greatest!"

Ambiguity just goes with the territory of language--any language--as people use it in their customary habit. Maybe in 90% of everyday conversation ambiguous language is precise enough. In the remaining 10% confusion demands clarification: "Which scalpel do you want, doctor?" Any speaker can speak (write) more precisely, less ambiguously, with practice and when required by circumstances.

I don't know whether English is the most difficult language to learn, or not. Children can learn any language, even two or three unrelated languages at the same time.

Yes indeed a child can learn any language but it usually starts with the spoken word
English is a lingua franca used by 2/3 of the world from basic pidgin upwards. At pidgin level English is easily picked up by most non native speakers. To graduate towards tertiary level fluency takes 20 years immersion. A language has 4 phases Listening - speaking - reading - writing. Each has levels of fluency

I think my OP must be separated from what we define as English style as opposed to unambiguous meaning as in a court of law. I believe we need to view this from the position of logical argument in the classical sense perhaps with a boolean approach in mind, so we can get away from opinionation

Its important to know how to answer "Did you or did you not kill that man?"

or perhaps

"I put it to you that you killed that man, did you not - yes or no?"

No - could imply - yes i did
Yes could imply yes i did not but may be mis understood as yes I did kill

You see how tricky this can get - and we are not even trying yet

So we need some logical rules here from those skilled in the arts pls

Robin

"I am a good liar, if not the best." This makes things even more uncomfortable.

And you and devil, because I DID go to the market today. I bought some spicy Thai food, ate some of it there, and brought home the rest, after playing 3 hours of Euchre with Yvette and a whole bunch of other fellers starting at 1 pm.

They can vouch for me. So it was not me who dunnit.