Two spaces after a period: Why you should never, ever do it. | Farhad Manjoo, Slate Magazine

Manjoo gets really worked up on this typographical issue. He uses a lot of words to explain his argument. But he does so clearly.

Correct use of spaces between sentences is not just a typographical issue. It's also an issue of clarity and consistency in the use of punctuation, in the structure of sentences and paragraphs. And typography also is an issue of aesthetics -- what looks good to readers.

He writes:

Every modern typographer agrees on the one-space rule. 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. Every major style guide—including the Modern Language Association Style Manual and the Chicago Manual of Style—prescribes a single space after a period. (The Publications Manual of the American Psychological Association, used widely in the social sciences, allows for two spaces in draft manuscripts but recommends one space in published work.)

Two other respected and well-known manuals on my desk also recommend one space: the Associated Press Stylebook, the "bible" of many journalists and other professional writers, and the Gregg Reference Manual, often found in business and government offices.

Manjoo explains clearly why and how so many people learned to put two spaces after periods. It's all about the monospaced characters used by old-fashioned typewriters. In the olden days, every character in typewriters was the same width -- unlike the characters in typesetting equipment (even in the olden days).

Manjoo writes:

Monospaced type gives you text that looks "loose" and uneven; there's a lot of white space between characters and words, so it's more difficult to spot the spaces between sentences immediately. Hence the adoption of the two-space rule—on a typewriter, an extra space after a sentence makes text easier to read.

However, with modern typewriters, first, and then with with desktop computers and popular desktop publishing software, the proportional type fonts long used in publishing became available to every one. And so, the need for two spaces in monospaced typing should have disappeared.

But as Manjoo points out, some teachers continue to tell students to use two spaces -- and past typing students remember that instruction. He concludes:

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."

Here's what I advise on this topic in Garbl's Editorial Style Manual:

spacing Put only one space after all punctuation marks--unless no space is needed, such as between adjacent punctuation marks and before and after a dash and a hyphen. This guideline applies to the colon, period and other punctuation marks at the end of a sentence: exclamation point, question mark.

To prevent a person's initials from splitting between two lines of type, don't put a space between them: T.S. Eliot. Also, don't put spaces before or after hyphens, dashes or virgules. But treat an ellipsis like a word, with a space before and after it.

Either put one space between paragraphs or indent paragraphs; doing both is usually redundant.

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This article is featured in today's (Aug. 2) Garbl's Style: Write Choices -- available at the Editorial Style tab above and by free email subscription.