Learning Objectives

  • Recognize the standard uses of apostrophes
  • Demonstrate the standard uses of apostrophes

With possessives, the apostrophe is used in combination with an s to indicate that a word literally or conceptually possesses what follows it. Singular words, whether or not they end in s, are made possessive by adding an apostrophe + s. 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.


  • a student’s paper
  • one hour’s passing
  • Illinois’s law or Illinois’ law
  • interviewees’ answers
  • her professors’ office (an office shared by two of her professors; if it were just one professor, we would write her professor’s office)

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.

Here’s a test you can use to determine whether an apostrophe is needed—we call it the “of” test. Try rewording the sentence and substituting the apostrophe with the word of.

Using an Apostrophe Using “of” test
my friend’s DVD the DVD of my friend
Beth’s zombie plan the zombie plan of Beth
James’s canned goods the canned goods of James

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

Plural Possessives

Making plural words possessive can be confusing at times because we so often add an s to a noun to make it plural. All of those s’s can be a little overwhelming, but the rules are pretty simple:

To make plural nouns that do not end in s possessive, add ’s.

the children’s scary books
the mice’s tiny tails

To make plural nouns that end in s possessive, add just the apostrophe.

my cats’ treasures
our zombie fortresses’ weaknesses

Now try applying these apostrophe rules yourself.