The em dash (—), or long dash, is probably the most versatile punctuation mark because it can be used in place of a comma, parenthesis or colon. This dash is the popular dash, the longer of the two dashes (en dash and em dash).
An em dash is twice as long as the en dash and three times longer than the hyphen. It is said to have derived its name from the length of hyphen. It is said to have derived its name from the length of letter ‘m’.
Also read En dash: the tricky dash
*It is used to separate a parenthetical phrase or clause in a sentence, i.e. extra (but removable) information on a particular expression.
- Most of the controversial things he said were true—absolutely.
- My father—the tall man in the middle—was President Hassani’s classmate.
- Tunde’s cousins—his uncle’s children—were at the ceremony to support him.
- Soldiers must understand the concept of SERE— Survival, Evasion, Resistance, Escape. Note that you can use a single em dash (as in 1 and 4 above) or double (2 and 3), depending on the context.
*You can use an em dash to indicate an afterthought (something that is thought of or added later).
- I’m bothered by the turn of events in the political arena—but that should not be my business.
- He kept telling me he wasn’t happy—or maybe I wasn’t listening.
*Also, writers use em dash to replace omitted, censored or unknown letters.
- P———are liars. You can’t even trust them with their own money.
- Listen up, ——, stop disturbing the peace of the neighbourhood.
- The last speaker, ——, was better than the first.
Note that the spaces above are replaced with two or three dashes. You can use either, but be consistent.
The em dash is a unique punctuation mark, though few writers use it because it is considered less formal. It is not difficult to use, but only used it where necessary in your formal writing.