RationalWiki's 2019 Fundraiser

There is no RationalWiki without you. We are a small non-profit with no staff – we are hundreds of volunteers who document pseudoscience and crankery around the world every day. We will never allow ads because we must remain independent. We cannot rely on big donors with corresponding big agendas. We are not the largest website around, but we believe we play an important role in defending truth and objectivity.

If everyone who saw this today donated $5, we would meet our goal for 2019.

Fighting pseudoscience isn't free.
We are 100% user-supported! Help and donate $5, $20 or whatever you can today with PayPal Logo.png!

Donations so far: $3220Goal: $6000

Quod erat demonstrandum

From RationalWiki
Jump to: navigation, search
Part of the series on
Logic and rhetoric
Icon logic.svg
Key articles
General logic
Bad logic

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[edit]

See the main articles on this topic: Danth's law and Begging the question

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;


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.