Em dashes, en dashes, and hyphens. The distinction between these three straight lines of minutely differing length is a topic only an editor could love. But it’s also the source of confusion and frustration among members of the tribe, and anyone who has to deal with us. Here’s my attempt at a quick and dirty guide.
These are the long ones, sized, theoretically, according to the width of a capital M in whatever typeface you’re using. They’re used to set off a chunk of a sentence from the rest of the sentence (in the same way you would parentheses, before certain kinds of lists, or to indicate a pause). See my earlier post on the em dash and its uses. Example: Editors—why don’t they notice that nobody cares about dumb little details like dashes?
As you may have already guessed, en dashes are the width of a capital N, making them the middle-sized punctuation mark of the trio we’re discussing. They are sometimes hard to distinguish from a hyphen. In virtually all cases, they are used to indicate a range of numbers. Example: The editor found 150–210 mistakes per chapter, though sometimes it felt like 150,000–210,000.
Hyphens are short but sweet. Their use is probably one of the most confusing issues in all of copyediting, and can’t fully be discussed in a post that I’ve already tried to sell as “quick and dirty.” Suffice to say that hyphens generally unite words (often compound modifiers). Example: I dreamed a beautiful dream of a word in which well-trained editors could charge $100 per hour.