An apostrophe is a punctuation mark used to indicate possession, to mark the omission of numbers or letters in a word, and to form the plural of lowercase letters. Apostrophes also prevent miscues in certain cases.
Marking the Omission of Letters
You are becomes You’re
Was not becomes Wasn’t
Is not becomes Isn’t
Showing possession
For singular nouns, add –’s to form the possessive.
John’s bike.
Shelby’s new job.
The apostrophe is used the same way if a singular noun ends in –s
The boss’s security cameras didn’t record the theft.
Mr. Davis’s new car is awesome. (Some style guides, however, require adding only the apostrophe: Mr Davis’ new car is awesome)
Plural nouns
To indicate possession for a plural noun ending in –s, place the apostrophe after the –s.
Her friends’ cars all arrived at the same time.
Reporters wanted the players’ thoughts on the new coach.
Note: plural nouns not ending in –s are treated as singular nouns:
The children’s shoes were covered in mud.
Joint possession
To show possession for two or more nouns, add –’s to only the final noun.
The boy and girl’s father forgot to pick them up.
Peter, Paul, and Mary’s new tour kicks off next month.
Possession for Compound Words
Use the apostrophe at the end of the compound word.
My father-in-law’s family came to visit us last weekend.
The ten-year-old’s new bike was stolen.
Possession and Indefinite Pronouns
Add –’s to the end of the pronoun.
Somebody’s home in the neighborhood was broken into.
Anybody’s children can attend the party.
Forming the Plural of Lowercase Letters and Preventing Miscues
You must mind your p’s and q’s.
How many P90X’s did you buy?
Commonly Confused
Possessive pronouns
Possessive pronouns don’t use an apostrophe.
Its (not it’s—it’s means it is)
The dog chased its tail.
Your (not you’re—you’re means you are)
I believe this is your problem.
Hers (not her’s)
Those shoes are hers, not mine.
Whose (not who’s—who’s means who is)
The neighbor whose car was stolen filed a police report.