There’s a piece of punctuation that I didn’t know existed until after I finished my PhD in Literature, after I had won an award for teaching writing, and after I got my first in-house editing job: the en-dash.
We all know hyphens, which connect a pair of words that are working together (as in, “a three-year drought” but not “the kid is three years old”) or a prefix to a noun (as in, “co-owner” or “anti-aircraft” or “re-press” or “neo-Marxist”).
Many of us also know em-dashes, which can be used in place of parentheses—if you like to interrupt yourself—or in place of a colon—for emphasis. When I encounter a writer who composes long, winding sentences, peppered with commas that sprawl, devan-style, across the page, and unfurl at great length, unravelling like a roll of film, I find that using em-dashes—albeit judiciously—can help support readability. But be careful—the em-dash is a glorious, promiscuous, and fertile piece of punctuation, which—if you’re not careful—will take over your writing and—I’m certain—come to annoy your reader.
It’s not technically correct to put a space on either side of the em-dash, but some people prefer the look. If you want to put a space before and after your em-dash, I recommend reducing the font size of that space (say, from your normal 12-point down to 6-point), because a full-sized space before and after an em-dash looks awkward.
The secret piece of punctuation, the en-dash, is only used in very specific circumstances. It can show range (as in, “pages 4–16” or “the Vancouver–Seattle leg of the trip”); it can show a relationship of two equal parts (as in, “a mother–son dance” or “the Spanish–American war”); or, it can be used if you have an unusual compound adjective (as in, “the Second World War–era dress” or “the Margaret Thatcher–style policy). Because those latter unusual compound adjectives can sound awkward, I’ll sometimes choose to rephrase them rather than use the en-dash.
I think that only editors notice the en-dash, and that it isn’t necessarily a problem if you don’t use them, because most readers won’t be confused if you use a hyphen to show a range or write about a “Second-World-War-era dress.” You won’t technically be correct, but I think that your readers will still understand you.
Now that I know about this secret piece of punctuation, though, I’ll always correct for it. If I’m editing your list of references and I discover that you’ve correctly used the en-dash to indicate page range, then you will have a very special place in my heart.