The Colon and Em Dash : —
Part 1 of 2
The colon is used in nonfiction mostly as an introducer for explanatory statements, examples, and series lists. It can be used for all of those purposes in fiction, too, but it finds much use in storytelling in its other function, which it shares with the em dash: setting off and drawing attention to ideas. The colon has a more formal, measured look, while the em dash apposes the ideas in a more abrupt and informal way. Since fiction is often informal or even conversational in style, and since fiction writers usually want set-off matter to have a more dramatic presentation, the em dash is probably used more often, but it’s your call. Both are correct and widely used.
Notice below that either works, but the em dash makes a more abrupt and emphatic lead-in to the information that follows it.
Mina heard a click on the phone line and realized the downstairs extension had been picked up: somebody else was in the house.
Mina heard a click on the phone line and realized the downstairs extension had been picked up—somebody else was in the house.
Em dashes used in this way have an effect different from that of parentheses or commas. Whereas parentheses tend to minimize the importance of what’s inside them, and pairs of commas essentially equalize enclosed material with what’s around it, em dash pairs point big flashing arrows inward toward the enclosed material.
I nearly dropped my teeth when Harvey Jackson (the only person we considered to be above suspicion) called to confess.
I nearly dropped my teeth when Harvey Jackson, the only person we considered to be above suspicion, called to confess.
I nearly dropped my teeth when Harvey Jackson—the only person we considered to be above suspicion—called to confess.
Like material inside parentheses, anything inside a pair of em dashes is compositionally insulated from the larger sentence around it. It can be just about anything you want it to be—a word, a phrase, a sentence fragment, or even, as we see below, an entire independent clause that could stand on its own as a sentence, but is here used as emphasized internal content.
The Ames brothers had deserted him when things got tough—he was disgusted with himself now for not having seen that coming—and now he was alone.
A pair of em dashes is also handy to clarify the distinction between internally punctuated items.
The example below has series items separated by commas:
Jim and Bobby Thomas, the new bobsledding team, and the TV crew were all opposed to the location.
How many series items are there above? Are “Jim and Bobby Thomas” and “the new bobsledding team” two separate series items separated by a comma, or is “Jim and Bobby Thomas, the new bobsledding team” a single item with an internal comma? There’s no way at all for us to know.
Jim and Bobby Thomas—the new bobsledding team—and the TV crew were all opposed to the location.
Above, we’ve changed “the new bobsledding team” from just another item in a series list of separate items into an emphasizing appositive that amplifies on what comes immediately before it. It’s now crystal clear that Jim and Bobby Thomas are the bobsledding team.