DASH

1. Em dash

The chief use of a dash or pair of dashes is to indicate a break in the flow of thought or an emphatic pause. Do not use three dashes in one sentence or overuse them on a page. Do not capitalize a complete sentence that follows a dash.

We were not happy—rather the reverse—at this turn of events.

Then we came to—shall we name the place?—Parkerville.

We enjoyed ourselves immensely—for 10 minutes.

Dashes may enclose a phrase that would be set off by commas but which itself contains commas:

There were four of us—Fred, Mary, Joe, and I—by the fire.

No mark of punctuation can stand before a dash except very rarely a question mark, an exclamation point, a parenthesis, or a bracket.

2. En dash

Use an en dash instead of a hyphen in compound modifiers when one or both of the elements is itself a compound:

Grand Staircase–Escalante National Monument

the Arizona–New Mexico border

Civil War–era house

first-class–second-class rivalries

Some special cases also use an en dash: University of Wisconsin–Milwaukee.

For a range of numbers or dates in display type or in map and graphic labels, an en dash may be used in place of a hyphen for readability:

1999–2000

20–25 people per square mile