Page 166 - Perfect English Grammar: The Indispensable Guide to Excellent Writing and Speaking

An em dash (—) is the width of an uppercase letter M.
It is used to set off portions of text that may be of secondary interest or even

tangential. It often connects two independent clauses with a related thought in
the same way parentheses or commas might, but the effect is much more

striking. The em dash is usually a substantial visual interruption. Different style
guides have different rulings on whether to include spaces on either side of an

em dash.

■ Nigel and Tamsin were married—we think they eloped to France—

and then they immediately set about starting a family.

A single em dash can be used to set off a condition or conclusion for
emphasis.

■ We’re wearing tuxedos to the birthday party—and that’s not up for
debate.

■ The fire marshal wants to condemn the building—but he has to go to
court to do it.

Em dashes can also be used to set off lists in an independent clause (see
section 5.4, Clauses), sometimes with a conjunction as part of the list, and

sometimes without.

■ The robust rustic menu—quail, rabbit, beets, morels, persimmons,

cider—was perfect after a long hunt.

Em dashes can also be used to show incomplete dialog.

■ “We’re getting the—,” she stammered. “I think we’re ready to—. Now

what?”

16.9 Apostrophe