When Do You Use Apostrophe S?

To be an expert in the English language, you need to master more than fluent speech. As a great writer, you’ll need to know a few rules that are unique to the written word. For example, a skillful writer understands where to place a punctuation mark and how to use quotation marks properly. In this article, we’ll be discussing a set of rules that apply to your writing, although they aren’t necessarily relevant when you’re speaking. The words “whose” and “who’s” sound the same, even though they’re spelled in different ways. Likewise, “cape’s” and “capes,” can’t be distinguished by ear, even though they have different meanings. So, today, let’s talk about apostrophe S. When is it appropriate to use, and what are the rules for tricky use cases?

Even in informal writing, the correct usage of apostrophe S can help your readers avoid confusion. In the following examples, we share advice for a situation where an apostrophe shows up. We recommend referring to your favorite style guide, such as Chicago Manual of Style, AP Style, or MLA Style to maintain consistency in your writing. Apostrophes should always be written as a single quotation mark and followed by a lowercase letter S (when applicable).

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Possessive Nouns

If you have a noun, such as “ball,” “Fred,” or “liberty,” you’ll need an apostrophe S to show possession. 

  • The ball’s surface
  • Fred’s Toyota
  • Liberty’s virtues

For all of these examples, the proper apostrophe use for the possessive form is straightforward. Unfortunately, not all nouns are so simple. What about proper nouns? In cases like the possessive form of “Peters,” as in “The Peters family,” things get a bit more complicated. Also, what about a name like “Louis,” where the name ends in an S?

Style guides offer differing opinions. All of the following may be considered, depending on the style guide you choose:

  • Alan Peters’s boat
  • Alan Peters’ boat
  • The Peterses’ boat (indicating joint possession by the whole family)
  • Louis’s desk
  • Louis’ desk

As you can see, for a singular proper name ending in the letter S, you can choose to either write an apostrophe or apostrophe S. Your choice would depend upon the style guide you’re using. Similarly, you could include an apostrophe or apostrophe S for any singular common noun ending in S.

  • The witness’s statement
  • The witness’ statement

Plural Possessives

For plural possessive nouns ending in S, simply add an apostrophe to the end of the word. 

  • The cats’ supper
  • The houses’ driveways 

For possessive plurals ending in another letter, the apostrophe rules would mimic those for a singular noun. Add an apostrophe plus the letter S.

  • The alumni’s donations
  • The men’s beards

Compound Ownership

When you come across compound nouns showing two people with possessive (shared) ownership, you only need to make one of the names possessive. On the other hand, if the ownership is not shared, you’d need to make both names possessive. 

  • Lisa and Doug’s vacation house. 
  • Lisa’s and Doug’s vacation houses. 


Anytime you write a contraction, you should replace omitted letters with an apostrophe. In some cases, such as when you contract the words “us” and “is,” you’ll be left with an apostrophe S

  • “Who is” becomes “who’s”
  • “Let us” becomes “let’s”
  • “He is” becomes “he’s”

Plural Nouns

Generally, when you make a singular noun into a plural, there’s no apostrophe involved. Car becomes cars. Boat becomes boats. However, as with most rules, we do see a few exceptions. There are three occasions when you may consider adding an apostrophe S when making a word plural. 


If you’re pluralizing a single digit numeral, you may add an apostrophe S for clarity. Most style guides do not recommend adding an apostrophe S for the numbers 10 and above. 

  • Fred was born in the 1970s.
  • I drew a pair of 9’s from the deck of cards. 


When you pluralize the letters of the alphabet, some style guides suggest you add apostrophe S.

  • He got B’s in math both semesters. 
  • Both of their names started with K’s. 

An Unusual Noun

When you pluralize a word that isn’t normally a noun, you may use apostrophe S.

  • She made a list of do’s and don’ts for the new hire. 
  • They got sick of hearing so many no’s. 

What About Possessive Pronouns?

Possessive pronouns don’t require apostrophes. 

  • His
  • Mine
  • Yours
  • Hers
  • Its
  • Ours
  • Yours
  • Theirs
  • Whose

In light of homonyms, you should be particularly careful to avoid apostrophe errors with possessive pronouns. Notice that “whose,” the possessive pronoun, sounds like “who’s,” the contraction for “who is.” Also, “its,” the possessive pronoun, sounds like “it’s,” the contraction for “it is.” If you can’t decide whether you need an apostrophe S, ask yourself whether the word contains missing letters from a contraction.

Whose/who’s dog is this?

She’s the one whose/who’s angry.

Its/It’s okay.

The monster stayed in its/it’s lair. 


  1. https://style.mla.org/apostrophes-three-ways/
  2. https://www.merriam-webster.com/words-at-play/what-happens-to-names-when-we-make-them-plural-or-possessive
  3. https://apvschicago.com/2011/06/apostrophe-s-vs-apostrophe-forming.html
  4. https://www.english-grammar-revolution.com/possessive-pronoun.html