Since I have a theme going with the more unusual beasts of punctuation, I thought I would do a little blurb on the em-dash. I didn’t learn to use it until college, and most of what I learned actually came from studying it in other people’s work (there’s nothing like reading for helping you with grammar; I usually can’t quote grammatical rules, but I can tell you if something sounds right or wrong, simply because I’ve read so much, I know what sounds correct). Many, many people are not taught how or when to use an em-dash, which is a shame, because it’s very awesome.
First, why is it called an em-dash? This is a typesetting reference: it is a dash that is the length of a printed letter “m.” There is also an en-dash, but you will rarely see it referenced, because most people just use a hyphen (I’ll admit, even I’m not sure when an en-dash should be used, as opposed to a hyphen).
Em-dashes can be similar to semi-colons, except instead of separating two sentences, they separate a sentence and a clause. In some places they are interchangeable with commas. They also offer a place to make an aside.
It was beautiful, different, and—for an American city—old.
Here we see the em-dash taking the place of commas. The sentence is still correct if you use commas (It was beautiful, different, and, for an American city, old), but I chose to use an em-dash mainly for aesthetic reasons. While commas abound in turn-of-the-century literature (and I’m rather more fond of them than most modern writers), they are not quite so popular now. For this sentence, replacing the commas with em-dashes keeps it from looking like I’m comma-crazy (despite the fact that they are all grammatically correct).
Why did I set “for an American city” in its own little em-dash brackets; why not something else? The only time you can use em-dashes in lieu of commas is when they’re setting off a clause. “For an American city” is a clause which modifies “old.” I am making it clear that “old” is a relative term (namely because the vampire enjoying the city is 800 years old). “Beautiful” and “different” are words–not clauses–describing “it” (i.e. the city).
At first he thought it was an animal—perhaps in someone’s trash—but then he decided it was too large to be a cat or dog.
This is an example of using the em-dash to create an aside. The sentence doesn’t require the clause, but it makes it clear why Anselm felt an animal might be the cause of the strange noise he was hearing.
If they were as strong as vampires—and it was safer to assume so than not—Anselm didn’t want to try to take on two of them at once.
This is another example of an aside. We see here Anselm’s exact rationale for why he didn’t want to try to confront the two strange vampires he’s stumbled across; he’s playing it safe.
It was very peculiar—like something metallic.
Here we see the em-dash functioning almost as a semi-colon. “It was very peculiar” is a sentence in its own right, but “like something metallic.” is not–thus why you can’t use a semi-colon here. The clause following the em-dash describes why “it” (i.e. the smell) is very peculiar.
He looked ordinary enough—ordinary enough to blend in with humans, as they did.
Here again we see a clause which elaborates on the sentence it is following. Now, you might ask why I wrote the sentence that way. Why didn’t I write, “He looked ordinary enough to blend in with humans, as they did,” instead? I could have written the sentence that way–and it would have been perfectly correct–but instead I chose to write in this slightly more fragmented style because the reader is in Anselm’s head at the moment. People do not speak or think in clean, complete sentences. While I do not write incomplete sentences in general text, I have no qualms about putting them in dialog. Likewise, when the reader is seeing something through the eyes of one of my characters, I will generally describe the thing as a person would see it and think about it–complete with incomplete phrases.
“Dearest, I was never mad at you. Mad at myself, perhaps, but not at you.”
Here’s an example of dialog where the second sentence is incomplete, and yet it makes perfect sense in context. Why didn’t I use an em-dash in this case? It could have been used, but that’s not the way I want the sentences read. If I had used an em-dash, you would have read both portions as one sentence. “Dearest, I was never mad at you–mad at myself, perhaps, but not you.” I wanted the pause that comes with a period. The second sentence is meant to be said almost as an afterthought to the first sentence, not as a continuation of it. It’s a subtle difference, but it’s much more noticeable if you read it aloud (and I’m a stickler for having dialog that sounds real when it’s spoken).
Edited to Add: Our Case–Please Hear Me Out–Against the Em Dash. This is a recent article on Slate.com railing against the overuse of the em-dash. The author overuses the em-dash to make a point, but at the same time, he creates the horrible writing of which he is railing against. The em-dash is not a force for grammatical evil, which I think he implies, but like anything, it can be misused and make a piece of writing worse instead of better. No one wants to constantly read asides anymore than they want to read a word repeated too many times in a short space.
“Hey, look at that,” Bob said.
“That’s weird,” Bill said.
“I think it’s a bird,” Bob said.
“I think you’re crazy; that’s a weather balloon,” Bill said.
He also seems unaware of the fact that punctuation usage changes over time. While he is complaining that modern writers are using the dash too much now, he totally ignores the fact that 100 years ago, people used commas with abandon. And in some ways, we use them too little today. In short, the trend has moved away from commas. Perhaps writers today, though, are going with em-dashes to replace the loss. But regardless, writing styles change over time, and there’s nothing wrong with the em-dash coming into vogue, as long as it’s not abused.