The English professor was lecturing his first year students on the topic of grammar, specifically the requirement never to use a double negative.
“There are numerous spoken languages whose poorer quality practitioners are inclined to make use of the double negative such as in the example: I didn’t see Nothing!”
“This clearly is a ridiculous statement as the two negatives in it cancel each other out and produces the true meaning – I did see a thing, which is the exact opposite of what the person presumably meant, which was either: I did not see anything, or, I saw nothing.”
“In all of the languages where use of a double negative is used to produce a positive and contrary to intent statement there is never a case where a double positive is used to produce a negative one!”
The professor took a moment to draw breath before resuming his monologue, allowing just enough time for a student right at the back of the lecture theater to laconically drawl: “Yeaahh, Yeaahh…”.