Writing for The New York Times, Ben Yagodo reminisces on the magic of the em dash (—):

To get a sense of some of the things a dash can do, take a look at these pairs of quotes.

F. Scott Fitzgerald’s “The Great Gatsby”:

Thirty: the promise of a decade of loneliness, a thinning list of single men to know, a thinning briefcase of enthusiasm, thinning hair.

Thirty—the promise of a decade of loneliness, a thinning list of single men to know, a thinning briefcase of enthusiasm, thinning hair.

Henry James, referring to Henry David Thoreau:

He was worse than a provincial, he was parochial.

He was worse than a provincial—he was parochial.

Mark Twain in “Autobiography”:

…life does not consist mainly (or even largely) of facts and happenings. It consists mainly of the storm of thoughts that is forever blowing through one’s head.

…life does not consist mainly—or even largely—of facts and happenings. It consists mainly of the storm of thoughts that is forever blowing through one’s head.

Twain’s “Pudd’nhead Wilson’s New Calendar”:

Each person is born to one possession which outvalues all his others: his last breath.

Each person is born to one possession which outvalues all his others—his last breath.

In all cases, both versions make sense and are grammatically correct. But the ones with the dash (the ones the authors actually wrote) seem to live and breathe, while the others just lie there on the page. Like hitting the right combination of buttons in a computer game, typing two hyphens on the keyboard — and thereby making a dash — can give your prose a burst of energy, as if by magic.

Did you know the em dash is also known as a mutton?