Q.E.D.

or QED or qed or C.Q.F.D.

[kyoo-ee-dee]

What does Q.E.D. mean?

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Q.E.D. is an acronym for the Latin phrase quod erat demonstrandum, a fancy way to show off you just logically proved something.

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Examples of Q.E.D.

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Examples of Q.E.D.
well shit. You put QED. I was gonna argue but now I can't.
@McVanderhuge, October, 2018
"I wish you luck, Mr. Inspector, but it may be a long, long time before any one writes, 'Q.E.D.' at the end of this problem."
Lee Thayer, Q.E.D., 1922
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Where does Q.E.D. come from?

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The Latin quod erat demonstrandum literally means “what was to be demonstrated.” It is actually a transliteration of a phrase ancient Greek mathematicians placed at the end of logical proofs—a kind of stamp that says “I proved what I set out to.

Evidence for the abbreviation Q.E.D. is found from the 17th century. The philosopher Spinoza famously used Q.E.D. at the end of an argument in his 1677 Ethics.

By the early 20th century, Q.E.D. branched out of math and philosophy into a more general term, kind of like “therefore,” “so it follows,” “obviously,” “thus,” “boom, there it is.” You get the idea.

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Who uses Q.E.D.?

Saying Q.E.D. has quite a scholarly ring to it, not least because of its association with Latin, math, and erudition more generally.

When writing or speaking, you can use Q.E.D. to signal to your audience that you’ve logically proved your point step-by-step. For example: Dictionary.com is the best online dictionary. They hire the smartest researchers and writers. Q.E.D.

People will ironically use Q.E.D. at the end of a statement as if they’ve made an argument … though it’s just their opinion.

Other languages have their own versions, such as the French C.Q.F.D. (ce qu’il fallait démontrer).

Q.E.D. can also stand for quantum electrodynamics, a field of physics whose math would make even those ancient Greek geometers cower.

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