From The Washington Post authored by Avi Selk:

“In the beginning, the rules of the space bar were simple.  Two spaces after each period.  Every time.  Easy.

That made sense in the age of the typewriter. Letters of uniform width looked cramped without extra space after the period. Typists learned not to do it.

But then, at the end of the 20th century, the typewriter gave way to the word processor, and the computer,  and modern variable-width fonts.  And the world divided.

Some insisted on keeping the two-space rule.  They couldn’t get used to seeing just one space after a period.  It simply looked wrong.

Some said this was blasphemy. The designers of modern fonts had built the perfect amount of spacing, they said. Anything more than a single space between sentences was too much.

And so the rules of typography fell into chaos. “Typing two spaces after a period is totally, completely, utterly, and inarguably wrong,” Farhad Manjoo wrote in Slate in 2011.  “You can have my double space when you pry it from my cold, dead hands,” Megan McArdle wrote in the Atlantic the same year.  (And yes, she double-spaced it.)”

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