“Typing two spaces after a period is totally, completely, utterly, and inarguably wrong,” Slate columnist Farhad Manjoo writes in a recent editorial.
Old-fashioned typewriters used monospaced type, which produced a lot of white space between characters and words, so using two spaces after a period made the text easier to read, explains Manjoo. But as of the 1970s, monospaced type went out of style. Electric typewriters and computers now both use proportional fonts, eliminating the need for the extra space, Manjoo writes.
“Every modern typographer agrees on the one-space rule,” he says. “It’s one of the canonical rules of the profession, in the same way that waiters know that the salad fork goes to the left of the dinner fork and fashion designers know to put men’s shirt buttons on the right and women’s on the left.”
Then why are so many people still using the double-space? Manjoo says teachers are still instructing their students to use two spaces—which he calls an “ugly error"—simply because that’s the way they learned to type. But “we would never accept teachers pushing other outmoded ideas on kids because that’s what was popular back when they were in school. The same should go for typing,” he says.