A guide comparing Associated Press style and Chicago style for editors, writers, teachers, students, word nerds, and anyone else who gives a dollar sign, ampersand, exclamation point, and pound sign about style.

Apostrophe-S vs. Apostrophe: Forming Possessives of Words Ending in S (or an S Sound)

I once worked with a production artist who would use "comma" and "apostrophe" interchangeably.
Him: You want me to put a comma in "Season's Greetings"?
Me: Um, no.
Him: Then what's this mark?
Me: That's an apostrophe.
Him: That's what I meant!
Me: Hunh.
(Apparently, he wasn't alone in his indifference, hence the dubious term "air comma.")

The punctuation mark that most often gets mixed up with the apostrophe, by my estimation, is the single quotation mark. If smart (or curly) quote marks are toggled on, beware of employing a 6-shaped beginning single quote mark to do the job of a 9-shaped apostrophe: Whereas quote marks can face left or right, apostrophes only face one way. (Tip: Remember the mark in don't, or think of a backwards c.) Prepare to battle text-editing software which defaults to a beginning single quote mark when you begin a paragraph with an apostrophe or key it in after a space, such as for '80s, 'tis, 'cause, or rock 'n' roll (apostrophes, all of them).

For this blog entry, I'm going to focus on the difference between how The Associated Press Stylebook and The Chicago Manual of Style handle possessives for words ending in s or an s sound. In short, is it "Carlos' stylebook" or "Carlos's stylebook"?

Both AP and Chicago styles take pronunciation into account, handling new syllables formed by back-to-back sibilants in their own way. The style that many of us are accustomed to—simply adding an apostrophe after the s (e.g., "moss' growth") regardless of how the words sound—is a "formerly more common" alternative practice, according to Chicago, one which it does not recommend. But just between you and me, you can use this shoot-from-the-hip style in personal e-mail, where you are also free to forgo capitalization completely. (This may or may not be a test.)

General Rules for Forming Possessives

Plural Common Nouns Ending in S

AP and Chicago: Add an apostrophe.
  • the students' questions
  • the teachers' headaches

Singular Common Nouns Ending in S

AP: Add apostrophe-s unless the next word begins with s.

Chicago: Add apostrophe-s.
  • the duchess's hat
  • the duchess's style

Proper Nouns Ending in S

AP: Add an apostrophe.
  • Charlaine Harris' books
  • the Joneses' competition

Chicago: Add apostrophe-s if singular, and add an apostrophe if plural.
  • Socrates's tea
  • the Obamas' garden
  • Les's moor

Nouns Plural in Form, Singular in Meaning

AP and Chicago: Add an apostrophe.
  • the series' actors
  • the Academy of Motion Picture Arts and Sciences' history

Special Case: Nouns Ending in an Unpronounced S

AP: Add an apostrophe.
  • Descartes' thoughts

Chicago: Add apostrophe-s.
  • Camus's existence
  • the debris's cloud

Special Case: Singular Common Nouns Ending in S or an S Sound, Followed by a Word Beginning With S

AP: Add apostrophe.
  • for appearance' sake
  • for conscience' sake
  • for goodness' sake

Chicago: Add an apostrophe if the word ends in s; otherwise, add apostrophe-s.
  • for appearance's sake
  • for conscience's sake
  • for goodness' sake
Note: Proper nouns ending in s follow previously stated styles (e.g., "for Jesus's sake" in Chicago style).

Exception: Company Names With Apostrophe-S

AP: Use as is.
  • McDonald's profits (not McDonald's' profits)

So, to answer the question posed in the beginning ("Carlos' stylebook" or "Carlos's stylebook"?), the first is in AP style, the second is in Chicago style. Let's hope that Carlos picked the right stylebook.

  • AP, 2011: "apostrophe"; "Ask the Editor"
  • CMOS, 16th edition: possessives, 7.15-21


  1. Lol, considering buying an "air comma" mouse pad from UrbanDictionary.com.

    Anyway, great premise for a blog. I'll have to check out more articles.

  2. I love this post. I fear for the future of the apostrophe every day. Everything from Facebook status updates to professional signage these days seems to signal either a complete ignorance of how apostrophes are used or a blatant desire to disregard them.

  3. I enjoy this blog very much, but I wish it were updated more often. Please keep blogging!

  4. Les's moor...I see what you did there.

  5. Keeps it's shape…
    Keeps its shape…

    Frankly I would go with keeps shape. We are referring to a garment after it is washed. So what do you think? I think it needs an apostrophe…others disagree.

    1. It is not "keeps it is shape", therefore the latter is correct.

  6. "It's" is a contraction for "it is" or "it has." So you want "its." "His shape," "her shape," "its shape"—no apostrophe.

  7. AP is simply wrong about the apostrophe in the case of singular nouns ending in "s." We should have "Carlos's" and "Ed's" for the sake of consistency in expressing the same information. That virtue should trump consideration for whatever alleged psychic pain is experienced by seeing an "s" on both sides of an apostrophe. Stay the course, Chicago.

    David M. Brown

  8. Really good to see these tips and hope to see more.