Why you should never, ever use two spaces after a period.
Every major style guide—including the Modern Language Association Style Manual and the Chicago Manual of Style—prescribes a single space after a period.
Can I let you in on a secret? Typing two spaces after a period is totally, completely, utterly, and inarguably wrong.
And yet people who use two spaces are everywhere, their ugly error crossing every social boundary of class, education, and taste.* You'd expect, for instance, that anyone savvy enough to read Slate would know the proper rules of typing, but you'd be wrong; every third email I get from readers includes the two-space error. (In editing letters for "Dear Farhad," my occasional tech-advice column, I've removed enough extra spaces to fill my forthcoming volume of melancholy epic poetry, The Emptiness Within.) The public relations profession is similarly ignorant; I've received press releases and correspondence from the biggest companies in the world that are riddled with extra spaces. Some of my best friends are irredeemable two-spacers, too, and even my wife has been known to use an unnecessary extra space every now and then (though she points out that she does so only when writing to other two-spacers, just to make them happy).
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