rule of three

noun

, Mathematics.

1. the method of finding the fourth term in a proportion when three terms are given.

rule of three

noun

1. a mathematical rule asserting that the value of one unknown quantity in a proportion is found by multiplying the denominator of each ratio by the numerator of the other

Word History and Origins

Origin of rule of three¹

First recorded in 1585–95

Example Sentences

So, my wife and I vowed to implement the rule of three.

From Salon

It’s tentatively called “The Rule of Three,” and just like “We the Animals,” it tells the story of three brothers.

From Los Angeles Times

“Halfway through writing that book, I was coming up with even more, and I thought, it’s not going to fit in one book. So I was thinking two books, and if it’s two books it might as well be three. The rule of three kicked in. It seemed to make sense — it wasn’t daunting, because I found the material so enriching and compelling.”

From Seattle Times

“I call it the ‘rule of three’,” he said.

From Seattle Times

And Last: New doctrines: Carnahan’s Rule of Three: The longer one works to bring ironic Talmudic allusion and elegant Chaucerian wit to one’s entry, the greater the likelihood the winner will feature “drool,” “snot” or “poopy.”

From Washington Post