When—and how—to use an em dash
How to use em dashes
Em dashes can play many roles in fiction writing, taking the place of commas, colons, ellipses, or parentheses.
They are considered more informal than other punctuation marks. For the greatest effect, writers should use them sparingly when they want to draw a reader’s attention to something specific.
How to format according to CMOS
The Chicago Manual of Style (CMOS) recommends no spaces before or after the em dash. While there is no em dash key on a standard keyboard, there are a few ways to create an em dash:
Windows: Alt + 0151 (on numeric keyboard)
Insert double hyphens with no space before or after
Mac: Use "option + shift + -"
Origin of em dashes
The em dash, called so because it’s about as wide as an “m,” has been around since 1836, according to the Oxford English Dictionary, and first appeared in poetry, such as The Road Not Taken, by Robert Frost:
I shall be telling this with a sigh
Somewhere ages and ages hence:
Two roads diverged in a wood, and I—
I took the one less traveled by,
And that has made all the difference.
(From The Poetry of Robert Frost: The Collected Poems, edited by Edward Connery Lathem. Copyright 1916, 1923, 1928, 1930, 1934, 1939, 1947, 1949, © 1967 by Henry Holt Rinehart and Company. Copyright © 1936, 1942, 1944, 1945, 1947, 1948, 1950, 1951, 1952, 1953, 1954, © 1956, 1958, 1959, 1960, 1961, 1962 by Robert Frost. Copyright © 1964, 1967, 1968, 1970, 1973, 1975 by Leslie Frost Ballantine.)
In summary...
The em dash is a versatile punctuation mark used to create emphasis, show interruptions, and provide clarity. Just be sure to use them sparingly so as not to overwhelm the reader.
Thought provoking
Em dashes can be used to add extra information that, while not essential to the message, offers important insight into the character's thoughts or behavior.
“ . . . as Uncle Victor explained it, either it would need to be proven that talking to ghosts was impossible—a notion challenged by countless stories in the media—or it would need to be proven that while it might be possible, Gina did not possess such a skill.”
Robin T. Popp, The Ghost Whisperer’s Gambit
Note that the em dash adds a sense of importance to the set-off information as opposed to enclosing the language in parentheses, which would have the opposite effect.
Effective interrupters
Use an em dash when a character has been abruptly cut off by another character.
“Well, I’d sure love to stop and find out, but I’m busy with my rounds, so maybe we can continue this—”
"Shut up! Shut that damn mouth of yours."
Jojo Moyes, The Giver of Stars
Or to show a pause in a character's dialogue to add narrative:
"Look, I've had as much of you"--her eyes looked up and down his body--"as I can take in one day."
Or to add a side note in the middle of a character's thoughts:
Her best option—maybe her only option—was to call, apologize, and hope for the best. Well, maybe not her only option.
Attention grabbers
Em dashes are a great way to create a dramatic pause:
With a deafening rush of air, she swooped past the now fleeing group—and simply vanished, leaving only the lingering echoes of her haunting scream.
Robin T. Popp, The Ghost Whisperer’s Gambit
And are especially useful to focus a reader’s attention on surprising or unexpected information:
The company execs finally informed all of the employees of their decision—close the doors once and for all.
Embellishment superstars
You can use double em dashes to provide the nitty-gritty details of what surrounds the em dashes.
The colors—blues, yellows, and reds—were especially bright and cheery.