I can’t focus on my manuscript, which is, among other things, about ADHD. Stop laughing.
But I hadn’t forgotten that some of you asked about whether you add an apostrophe s in a word that ends with an s or a z. Chicago has gone back and forth about these issues over the years and editions. I started to write out the quote, but then I remembered, you don’t care. You are staring at your computer yelling “Indy, if we wanted to read Chicago’s version, we would have bought the damn book.”
Right, sorry. Here it is:
Chicago’s definitive rules on how to add apostrophes to words with “s” sounds at the end
1. It is now acceptable, nay, required, to add an s at the end of words that end with an s or z. Sorry folks.
2. Add an apostrophe s to words where the s is silent.
3. Add an apostrophe s to proper names that end in an s
but Lincolns’ marriage [this is different because “Lincolns” is plural]
Decartes’s three dreams
(Source: Chicago Manual of Style, 16th ed., 7.15–18)
Exception 1. If the plural and the singular is the same, do not add an s after the apostrophe (e.g., politics’ true meaning or United States’ role; CMOS 7.19).
Exception 2. This one I have to quote because it is really funny “For the sake of euphony a few for . . . sake expressions used with a singular noun that ends in an s end in an apostrophe alone…for goodness’ sake” (7.20)
This is a change from Chicago 15. But it’s the rules for standard American publishing. Now you know.