Editing, Tips and Tricks

Unpacking CMOS: Possessives

Originally published on The Scribe Source blog on Dec. 10, 2020.

Many aspects of the English language are tricky to navigate for one reason or another. Possessives—word forms that show ownership or relationship— are no different. But what are the current rules for forming a possessive?

Once again, The Chicago Manual of Style (CMOS) knows exactly where to begin. Using our editors’ favorite go-to guide, let’s dive into the particularities of possessives!

Possessive Forms (CMOS 7.16–7.18)

Let’s begin with the basics: singular and plural nouns that take the possessive form. 

Singular and Plural Nouns

The simplest possessive form is that of the singular noun. Whether it’s a common noun or proper noun, simply add an apostrophe (’) and s, whether or not the word already ends in s

The plural possessive is quite simple too: just add an apostrophe (’).

Consider the following:

My sister’s violin sounded like the screams of the damned before she started practicing. (singular possessive)

I studied the food and music in Charles Dickens’s works for my term paper. (singular proper noun ending in an s)

My grandparents’ famous blackberry pie is criminally delicious. (plural possessive)

If the plural noun is irregular and doesn’t end in s, the rule is the same as it is for the singular possessive form: add an apostrophe (’) and an s. Consider the following:

The children’s rooms are clean for once!

Have the Rules Changed?

If you learned grammar more than a few years ago, you may be saying, “Hold up! If a name ends in s, you just use an apostrophe! We say Jesus’, not Jesus’s.” Well, that was the case for many years, and many (if not all) of our editors were taught this rule as students. However, the standards have changed in the last several years, simplifying a great deal. 

So now, instead of trying to remember a dozen exceptions to the possessive rule, you can reduce it to a simple instruction in most cases:

Add an apostrophe and an s if the noun is singular or if it’s plural but doesn’t end in s; add only an apostrophe if the noun is plural and ends in s.


You can follow the same general rule for abbreviations. A word of warning, however: CMOS discourages using the possessive form of an abbreviation that’s immediately followed by the abbreviation spelled out. A little rewording fixes that right up! 

For example, replace this:

CMOS’s (The Chicago Manual of Style) rules for possessives are helpful for both editors and writers. 

with this:

The rules for possessives according to CMOS (The Chicago Manual of Style) are helpful for both editors and writers.

Exceptions to the Rule (CMOS 7.20–7.22)

Using the possessive form can be tricky when you’re working with a noun that ends in s and doesn’t change form when plural (think of words such as politics). In this case, only use an apostrophe. If this looks or sounds strange, then CMOS suggests rewording, using of to clarify the sentence. 

Consider the following:

That was this particular werewolf species’ last known appearance. (adding only an apostrophe)

That was the last known appearance of this particular werewolf species. (using of to clarify)

Similarly, add only an apostrophe to the possessive form when the name of a place, organization, or publication is a plural form ending in s, even though the noun itself is singular (e.g., the New York Times’ latest article). 

A few For . . . sake expressions—for goodness’ sake and for righteousness’ sake—only use an apostrophe for the possessive. However, the normal possessive rules can apply for other expressions, such as for Pete’s sake.

Joint, Separate, and Compound Possessives (CMOS 7.23–7.27)

This can get a little more complicated. Luckily, the particulars of possessives can be neatly categorized.

Joint and Separate Possessives

When two nouns are closely linked and the noun is possessed by both, the possessive form only needs to be applied to the second element. This is an example of joint possession. Consider the following:

My brother and sister’s apartment is on the fifth floor, and the elevator is broken.

However, when the nouns possess separate items, both linked nouns should be in the possessive form. This is an example of separate possession. Consider the following:

My brother’s and sister’s flower arrangements are both wilted.

Compound and Double Possessives

When compound nouns take the possessive form, whether singular or plural, only the final element needs to show it. For example:

The assistant henchman’s ambition shocked the big, bad villain. (henchman takes the possessive, though assistant does not)

The double possessive, or double genitive, is a possessive form preceded by of. The implication is that the possessed noun is one of several. The double possessive can easily be confused with wording that sounds similar but doesn’t use the possessive at all. If that’s the case, then no possessive form is needed. 

Consider the following:

Are you a friend of Jason’s? I could have sworn you were a friend of his. (possessive)

I am a student of experience. (not possessive)

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