The Rules for Using an En Dash
THE EN DASH
We use the en dash for three things:
First, to separate inclusive numbers and words representing dates, time periods, or references: 1962–1975; 2:00–5:00 p.m.; April–June; Chicago Manual of Style, 6.32–6.42.
Here’s another little pile they’re waiting for us to step in: the en dash does not mean “to” or “and”; it may not follow a preposition: to write “from 2008–2012” is incorrect, and so is “between Tuesday–Friday.” The correct way is: “from 2008 to 2012” and “between Tuesday and Friday.” But we may write, “The store is open Tuesday–Friday,” because no preposition precedes it.
Second, use the en dash when the end date has not yet been determined: “Pat Benatar (1953–).”
Grammar Guru of The Washington Post, Bill Walsh, calls hog-wash on the en dash; absolutely no need for it; just use the hyphen, a perfectly good separation. I agree, sort of; but there’s this . . .
. . . third situation, which admittedly will not come up often, where one element in a “compound” adjective or “compound” noun is “open” or already hyphenated.
A “compound” is two or more words that act together as a unit. “New York” is an “open” compound. When we combine it with another word to describe “line,” we separate "New York" and the next word with an en dash: “The New York–Boston line.” Where one or both compounds are already hyphenated, we also need to separate them with an en dash: “the pre-formed–pre-manufactured home”
I suspect the en dash will continue to muscle its way onto the page, and it does distinguish in a way the hyphen cannot, so we should try to use it correctly.
HOW TO MAKE AN EN DASH
Type a word, hit space, tap “-” twice, hit space again, and type the following word. Microsoft Word will automatically turn that double hyphen into a dash the width of a small case n, or an en dash. Then remove the spaces on either side.
Alternatives: on a PC, go to Insert -> Symbol -> More Symbols -> Special Characters; highlight “En Dash” and click “Insert.” On a Mac, hold down “option” and tap “-.”
I have said many times that when you get the finer points of grammar correct, you send the impression to your readers (many of whom know the difference) that you are competent and informed about many other things. But don’t wipe your shoes just yet; the pile gets much deeper next week.