Quod erat demonstrandum
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Logic and rhetoric
Quod erat demonstrandum (normally abbreviated to Q.E.D.) is a Latin phrase that means literally "that which was to be demonstrated."
In normal English, this means "thus it is proven," or "so there, nyer nyer nyer". It is used formally after the last line of a proof, and colloquially in discussion or argument in a similar fashion.
Due to the scary nature of Latin, many people have been misled into thinking it actually stands for "quite easily done," which stems from math teachers who — thinking they are clever — tell this joke without identifying it as such.
This ignorance is actually a godsend (or, alternatively, a curse), as it allows the educated to correct their cretinous peers in as condescending a manner as they feel necessary.
As a fallacy
While fancily ending a syllogism of one's proposal with "Q.E.D." totally sounds like something a college dean — learned at the topic at hand — might do, doing so is actually not the least bit indicative of said argument being logically acceptable.
Here's an example of the "Q.E.D. stamp" being applied to a blatantly fallacious argument;
- 10% of car thefts are committed by left-handed people.
- Half of all polar bears are left-handed.
- There's a 5% chance your car was stolen by a polar bear.
As such, treat unexamined claims of Q.E.D for what they most likely are — mere
pretentious latin shorthand for shouting "Nailed it!!" while touring the room for hi-fives.