When to Use Apostrophes

Learning Objectives

  • Demonstrate the standard uses of apostrophes to show possession
  • Demonstrate the standard uses of apostrophes in contractions
Appropriate alternative text for this image can be found in the caption.

Figure 1. An apostrophe.

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 example:

  • a student’s paper
  • one hour’s passing

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. For example:

  • 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.

Try It

Take a minute to test your knowledge about apostrophes.

How did you do? Most people get confused with using apostrophe to show ownership, or possession.

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.

Try It


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. While you should follow your teacher’s preference, keep in mind that leaving out contractions can often make your words sound too formal and stilted. (And you shouldn’t eliminate contractions in your papers just to up your word count!)

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 remember that possessive pronouns never have an apostrophe. Try replacing the word in question with the expanded version of the contraction and seeing how it sounds.

I think it’s going to rain → I think it is going to rain.

If the word can be replaced by two words (it’s → it is) then it is a contraction and it needs an apostrophe (because, 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.

Acronyms and Numbers

In technical writing, acronyms and numbers are frequently pluralized with the addition of an apostrophe + s, but this is falling out of favor, and there is typically no need to put an apostrophe in front of the s. For example, SSTs (sea surface temperatures) is more acceptable than SST’s when your intention is simply to pluralize.

Ideally, with an acronym or number, use the apostrophe before the s only to show possession (i.e., “1860’s law”; “DEP’s testing”) or when confusion would otherwise result (“mind your p’s and q’s”).

You can also use an apostrophe to stand in for omitted numbers.

EXAMPLE: I was born in ’75, so I’m feeling old these days.

Now take a minute to see how you do with acronyms, contractions, and replacing numbers using apostrophes.

Try It

It is important to note that the use of contractions and the use of apostrophes to stand in for omitted numbers are generally considered too informal for most academic writing. Some students wonder why they should bother learning these rules. The answer is that there are plenty of writing situations in which contractions are appropriate. Sometimes contractions are too considered too informal for most papers you write for college.


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