Type professionals can get amusingly—if justifiably—overworked about spaces. "Forget about tolerating differences of opinion: typographically speaking, typing two spaces before the start of a new sentence is absolutely, unequivocally wrong," Ilene Strizver, who runs a typographic consulting firm The Type Studio, once wrote. "When I see two spaces I shake my head and I go, Aye yay yay," she told me. "I talk about 'type crimes' often, and in terms of what you can do wrong, this one deserves life imprisonment. It's a pure sign of amateur typography." "A space signals a pause," says David Jury, the author of About Face: Reviving The Rules of Typography. "If you get a really big pause—a big hole—in the middle of a line, the reader pauses. And you don't want people to pause all the time. You want the text to flow."
This readability argument is debatable. Typographers can point to no studies or any other evidence proving that single spaces improve readability. When you press them on it, they tend to cite their aesthetic sensibilities. As Jury says, "It's so bloody ugly."
But I actually think aesthetics are the best argument in favor of one space over two. One space is simpler, cleaner, and more visually pleasing (it also requires less work, which isn't nothing). A page of text with two spaces between every sentence looks riddled with holes; a page of text with an ordinary space looks just as it should.
Is this arbitrary? Sure it is. But so are a lot of our conventions for writing. It's arbitrary that we write shop instead of shoppe, or phone instead of fone, or that we use ! to emphasize a sentence rather than %. We adopted these standards because practitioners of publishing—writers, editors, typographers, and others—settled on them after decades of experience. Among their rules was that we should use one space after a period instead of two—so that's how we should do it.
Besides, the argument in favor of two spaces isn't any less arbitrary. Samantha Jacobs, a reading and journalism teacher at Norwood High School in Norwood, Col., told me that she requires her students to use two spaces after a period instead of one, even though she acknowledges that style manuals no longer favor that approach. Why? Because that's what she's used to. "Primarily, I base the spacing on the way I learned," she wrote me in an e-mail glutted with extra spaces.
Several other teachers gave me the same explanation for pushing two spaces on their students. But if you think about, that's a pretty backward approach: The only reason today's teachers learned to use two spaces is because their teachers were in the grip of old-school technology. 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. So, kids, if your teachers force you to use two spaces, send them a link to this article. Use this as your subject line: "If you type two spaces after a period, you're doing it wrong."
Correction, Jan. 18, 2011: This article originally asserted that—in a series of e-mails described as "overwrought, self-important, and dorky"—WikiLeaks founder Julian Assange used two spaces after every period. Assange actually used a monospace font, which made the text of his e-mails appear loose and uneven. (Return to the corrected sentence.)