Mad Dash: How to Use the Dash in Writing - Ben Yagoda, NYTimes.com

Yagoda's column jumps right in to explaining clearly the two main uses of the dash (also noting that a dash is not a hyphen). And he explains how to use them for those purposes.

Summarized, here they are:

• the Pause Dash. It more or less says to the reader, “Right here, I want you to take a breath. ..."

• the Parenthetical Dash, in which dashes are deployed in pairs and set off nonessential elements of the sentence.

He also notes a third purpose--"to indicate disjointedness"--that doesn't follow any rules.

Yagoda continues by describing how well-known writers have used dashes. The examples help put a real-life context around the rules.

My online editorial style manual on dashes provides similar advice:

dash (--) Long dashes, called em dashes, have three main uses. In these uses, em dashes are usually less formal but more emphatic substitutes for other typical punctuation marks. To preserve the impact of dashes, avoid overusing them.

First, use an em dash to explain, justify or stress in the second part of a sentence something in the first part: Fans filled all the seats--the concert hall was packed! The new shopping mall will open Tuesday--if the air-conditioning works. The project was finished on time, within scope--and under budget. The manager was new to the agency--brand new.

Second, use a pair of em dashes to make an emphatic pause or abrupt, parenthetic change in thought within a sentence: The new auditorium--opening six months behind schedule--is getting praise from both critics and audiences. If you'd prefer to play down such a phrase, consider placing it between parentheses instead, or between commas.

Third, use a pair of em dashes to set off a phrase that has a series of words separated by commas: Leif Nelson described the qualities--intelligence, a sense of humor and compassion--he wants in a manager.

As shown in the examples above, do not put a space before or after an em dash (an exception to the rule followed by the Associated Press for newspaper use). Avoid using more than one pair of em dashes in a sentence.

A short dash, called en dash, may be used to mean up to and including when placed between numbers, times, dates and other uses that show range: 1993-96, $25-50, $432,000-$560,000 (but $25 million to $50 million), 55-65 years, 7:15-7:30 a.m. (but 9 a.m. to 3:30 p.m.), ages 15-20, pages 167-78. It also may be used to replace to and versus in capitalized names: the Chicago-New Orleans train, the Huskies-Cougars game. Do not put spaces before and after the en dash. 

Note: A hyphen (-) is not a dash. Most current word processing and design software can create em dashes and en dashes. If not possible, use two hyphens to create an em dash, and substitute a hyphen for an en dash. In Microsoft Word, if you don't space after the second hyphen, the two hyphens become an em dash. 

My style manual also provides advice on using hyphens.

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Yagoda's article is featured today (Oct. 25) in my daily online paper, Garbl's Style: Write Choices--available at the editorial style tab above and by free email subscription.