“But Karen, that makes no sense!” Not yet, it doesn’t, because I haven’t told you what it means. Hold yer horses; we’re going for a little ride.

It’s covered in the Chicago Manual of Style, 16th Ed., under section 7.84: Omission of part of a hyphenated expression. “When the second part of a hyphenated expression is omitted, the hyphen is retained, followed by a space.” That is a concise statement, but doesn’t really explain the why of the practice.

You know how I like to go on about GUM issues. Heh.

 
I’ll use an example from some of the work I’ve done in the last couple of days. The writer nailed it out of the gate; I made no correction (I didn’t need to!) or comment, but she queried me anyway. Nothing wrong with doing that. Also, there was nothing wrong with her writing. So, here we go.

“Make it a two- or three-course meal.”

What’s that hyphen doing after “two?” It’s indicating that there’s an understood word (one that’s not physically present, but that is contextually present) attached to “two,” and it appears later in the sentence attached to another similar word (in this case, the word “three”). Rather than repeating the same word twice (or more, in some cases), you can eliminate it and retain the hyphen from the full construction to indicate the actual sense to the reader.

Huh?

Rather than saying “Make it a two-course or three-course meal” you can remove the first “course” but retain the hyphen attached to “two.” “Make it a two- or three-course meal.” It works backward for a reader. When you see a hyphen attached to a word in that way, you have a signal that there’s a word later in the sentence attached to another similar word in the same way, and that will give you the full sense of what’s being said.

And of course now I could go for a three-course meal. Indian or Thai?