Editor's Note:

This blog post was originally written a decade ago, but there is still a heated debate between those who prefer adding only an apostrophe to a singular noun that ends in -s (e.g., Dickens' book) and those who prefer "apostrophe s" (e.g., Dickens's book). Recently The Associated Press (AP) published an article on this ongoing argument about how to style the possessive form of Vice President Kamala Harris. While everyone agrees that the possessive form of her running mate, Governor Tim Walz, is Walz's, the argument for Harris' vs. Harris's persists.

Which side do you agree with: AP (Harris') or others such as the The Chicago Manual of Style, The New York Times, and Ellii (Harris's)? You can watch the video below and/or read the following original post to see why Ellii chooses the latter. In fact, we update any AP articles in our That's News to Me section into our own house style so that we don't confuse students any further. If only all style guides could agree!

Original Post

(from April 17, 2014)

“Apostrophe s” (’s) is used for several reasons in English, such as for the contracted form of is and has, and also for indicating possession (belonging to someone). In general, we add ’s to a singular noun and add ’ to a plural noun ending in ‑s. For example, we would say the student’s book (for one student) and the students’ classroom (for many students). 

But what happens when the singular noun ends in ‑s? The rules for this have gone back and forth, which makes it difficult for both ELLs (English language learners) and speakers whose first language is English. As an editor, I have to keep up with the current guidelines as set out by popular style guides such as The Chicago Manual of Style. I thought I’d share the most recent “rules” with you so you can pass them along to your students! If you disagree with any of these guidelines, please share your opinion in the comment section below—it’s always interesting to learn what different teachers think around the world!

General Rules

1. Add ’s (apostrophe + s) to a singular noun

• the student’s book

2. Add ’ (apostrophe only) to a plural noun ending in -s

• the students’ classroom

Rule for Singular Words Ending in ‑s

Add ’s (apostrophe + s) to a singular noun that ends in -s

• the class’s door
• Kansas’s laws
• Dickens’s stories

According to The Chicago Manual of Style, 17th edition, the general rule for forming possessives also applies to words ending in -s (sections 7.15–7.19). This rule applies to both common nouns and proper nouns (including names ending in -s, -x, and -z), as well as letters and numbers. Here are a few more examples from The Chicago Manual of Style:

• a bass’s stripes
• Marx’s theories
• Borges’s library
• Berlioz’s works
• FDR’s legacy
• 1999’s heaviest snowstorm
• the Lincolns’ marriage (plural of the last name “Lincoln”)
• the Williamses’ new house (plural of the last name “Williams”)

The Chicago Manual of Style also explains that nowadays, unlike in previous years, words ending in unpronounced -s and proper classical names of two or more syllables that end in an "eeze" sound also follow the same rules, as noted in the following examples:

• Descartes’s three dreams
• the Ganges’s source

Basically, this is great news for us all because the same rules apply to almost every situation and are therefore easier to remember. English learners are always relieved when there aren’t a lot of exceptions to a rule!