What amazes me with double negatives is the usage in questions where the questioner expects a negative answer:

Setup:
Buses from a certain station leave to Airport or Train Station. No bus stops at both destinations.

Scene 1:
A bus is approaching a bus stop. The sign on the bus reads "Airport". The question might be: "Isn't this bus going to the train station?" and the bus driver answers: "No" -- meeting the expectance of the questioner. (What would've happended if the bus driver would have answered "Yes"?)

Scene 2:
A bus is approaching a bus stop. The sign on the bus reads "Airport". The question might be: "Is this bus going to the train station?" and the bus driver answers: "No".

Guido

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