Lesson: One space or two after a period

This recent Slate article reignited an old battle for typographers, punctuation geeks, and old-school users of typing instruments: Is it one space or two after a period?

I hate to break it to the two-space camp, but the authorities say you’re wrong. (Who am I kidding? I love to break it to you. An easy way to turn your usually friendly copy editor into an expletive-spewing beast is to turn in page after page—after page after page after page—of periods with two spaces.)

It’s official, the rule is: Only one space goes after periods.

How did we end up with this spacebar scandal? It goes back to the dusty days of typewriters. Typewriters used monospaced typefaces. This means every letter took up an equal amount of space on the page. A lowercase i was the same width as a capital W. And a period took up the same space as the W, too. Because of this, legions of typing teachers instructed students to insert two spaces after the period so that the visual break between sentences would be more apparent and would thus help with reading ease.

When word processors burst on the scene, bringing with them an array of font choices with proportional spacing, the second space after periods became unnecessary. These days when you’re composing a Word document or an e-mail, as long as you don’t choose a monospaced typeface (like Courier), the spacing built into the font will take care of the visual breaks for you.