Q. I’m having trouble finding guidance in CMOS about the minimum length of the final line of a paragraph (anywhere on the page). When proofreading, how do we determine whether a line is too short (or a “runt”)? I learned that it’s four characters minimum, but I can’t find CMOS confirmation of that. And then can an ellipsis be on a line on its own, and if not, should copyeditors use a nonbreaking space before a paragraph-ending ellipsis? What if there’s a closing quotation mark after it? Thanks!
A. According to CMOS 2.121 (on proofreading for overall appearance), “The last word in any paragraph must not be hyphenated unless at least four letters (in addition to any punctuation) are carried over to the final line.” You can extend this to mean that a paragraph-ending word on its own line should ideally be at least four letters long. But whatever your definition of what constitutes a “runt line,” it’s mostly a matter of taste (and applies only to print and other fixed layouts). Some publishers set a minimum of three letters; others go with as many as five. If in doubt, proofreaders should ask before starting in on the text.
As for ellipses, a paragraph-ending ellipsis on a line by itself, even if it’s followed by a quotation mark, is best avoided if you’re following a four-letter-plus-punctuation minimum (you can ignore the spaces between the dots and count the ellipsis as equivalent to a three-letter word). It’s probably best avoided anyway so it’s not mistaken for a section break.
Copyeditors, however, don’t usually decide such things. Though it’s generally a good idea to insert nonbreaking spaces within your ellipses to keep them from breaking at the end of a line as you edit (which can be annoying for you and anyone who reviews the document), you can usually leave decisions about paragraph endings to the typesetter or whoever will be preparing the document for publication.
See also CMOS 12.59–69 (on ellipses).