When to Use Apostrophes

Learning Objectives

  • Demonstrate the standard uses of apostrophes to show possession
  • Demonstrate the standard uses of apostrophes in contractions

With possessives, the apostrophe is used in combination with an s to indicate that a word literally or conceptually possesses what follows it.

PRO TIP: The easy way to think about this is to use the “of” test. Try rewording the sentence and substituting the apostrophe with the word of.

Singular Possessives

Singular words, whether or not they end in s, are made possessive by adding an apostrophe + s.

Examples: possessives

  • a student’s paper = the paper of a student
  • one hour’s passing = the passing of one hour
  • Illinois’s law or Illinois’ law = the law of Illinois
  • their professor’s office = the office of their professor (just one!)

If you just mean to make a word plural, you should not add an apostrophe.

Example: Incorrect use of Apostrophes

Here is an example of incorrect usage:

  • The student’s planned to buy their books but played Xbox instead.

Here, you would not use an apostrophe because there is no ownership being established. You can double-check this example and see that this use of the apostrophe would not pass the “of” test:

  • The planned of the students just does not make sense.

The sentence above would not pass the test and should read as follows:

  • The students planned to buy their books but played Xbox instead.
Appropriate alternative text for this image can be found in the caption.

Figure 1. An apostrophe.

Plural Possessives

For plural words, we typically indicate possession simply by adding the apostrophe without an additional s. However, for a plural that does not end in an s (e.g., bacteria), we would add an apostrophe + s.

Possessive forms of plural words can sometimes be confusing because we often add s to make a noun plural. With all those s’s, it may seem overwhelming, but the rules are actually quite simple:

  • To make plural nouns that do not end in s possessive, add ’s.
  • To make plural nouns that end in s possessive, add just the apostrophe.

Examples: Plural Possessives

Plurals not ending in s:

  • the mice’s footprints
  • The children’s playground = the playground used by children
  • The alumni’s reunion = the reunion attended by the alumni

Plurals ending in s:

  • my cats’ treasures
  • interviewees’ answers = the answers of the interviewees (multiple)
  • their professors’ office = the office of their professors (an office shared by two or more of their professors)

Writers sometimes mistakenly add apostrophes to make words plural, but this is not how the apostrophe is used; the apostrophe is used to show possession or ownership.

Now try applying these apostrophe rules yourself.

Try It

Take a minute to test your knowledge about apostrophes.

Contractions

A contraction is a shortened phrase. “He will” becomes “he’ll”, “are not” becomes “aren’t”, “would have” becomes “would’ve”, and “it is” becomes “it’s”. In all of these cases, the apostrophe stands in for the missing letters.

You may find yourself being steered away from using contractions in your papers. Some feel that contractions are stylistically inappropriate in formal writing. Follow your teacher’s preference, but keep in mind that leaving out contractions can often make your words sound too formal and stilted.

To Apostrophe or not to apostrophe

Possessive pronouns vs. contractions

  • your vs. you’re
  • its vs. it’s
  • their vs. they’re

All three of these pairs are the same kind of pair: a possessive pronoun and a contracted version of a pronoun + to be (you’re = you are; it’s = it is; they’re = they are). These are easy to mix up (especially its/it’s) because—as we’ve learned—an apostrophe + s indicates possession. The best way to use these correctly is to try replacing the word with the expanded version of the contraction.

  • I think it’s going to rain → I think it is going to rain.
  • It’s always means it is.

If the word can be replaced by two words (it’s → it is) then it is a contraction, and it needs an apostrophe (remember, the apostrophe is there to replace the missing letters).

  • I don’t want to go to your play → I don’t want to go to you are play.

If the word cannot be replaced by two words (your → you are) then it does not need an apostrophe.

  • You’re always means you are.

And if you are not sure, you can always avoid you’re and it’s without sounding stilted. You are always able to avoid certain words; it is not that hard to do!

Try It