The English Department's
Quick Guide to Using Apostrophes

Use an apostrophe to show that a noun possesses something.

If the noun is singular, add an apostrophe and an s.

That is Mary’s car.
The boy’s bike was in the driveway.
My dog’s name is Loki.
I have always enjoyed Keats’s poetry.

For plural nouns ending in s, add only an apostrophe.

He bought fifty dollars’ worth of CDs.
The teachers’ lounge is down the hall.
Ladies’ dresses are on the fourth floor.

For plural nouns that do not end in s, add an apostrophe and an s.

The children’s teacher was Ms. Delaney.
The men’s room is at the back of the restaurant.

Use an apostrophe to show that something has been left out of contractions.

I didn’t tell you that. (did not)
He wasn’t in school today. (was not)
It’s hot outside. (it is)
Fred was a member of the class of ’98. (1998)
She’d be much prettier if she’d cut her hair. (she would)
It’s four o’clock. (it is; of the clock)

Warning: Do not use an apostrophe to form plurals!

There are exceptions to this rule, but these are so rare I’m not going to bother with them here (consult a good grammar book if you’re curious).

Wrong: I went to visit the Johnsons’ today.
Wrong: I went to visit the Johnson’s today.
Right: I went to visit the Johnsons today.
Wrong: The girl’s are playing outside.
Wrong: The girls’ are playing outside.
Right: The girls are playing outside.

Warning: Personal pronouns do not take an apostrophe. Don't put one in at all in these cases!

Wrong: That book is your’s; this book is mine.
Wrong: That book is yours’; this book is mine.
Right: That book is yours; this books is mine.
Wrong: Jimmy is a friend of their’s.
Wrong: Jimmy is a friend of theirs’.
Right: Jimmy is a friend of theirs.

Warning: Do not confuse it’s with its or who’s with whose.

It’s is a contraction of it is or it has.

It’s not my fault! (it is)
It’s been raining for three days. (it has)

Its is the possessive form of it.

The dog was in its house. (the house belonging to it)
The picture was enhanced by its frame. (the frame belonging to it)

Who’s is a contraction of who is or who has.

Who’s in charge here? (who is)
Who’s got some money? (who has)

Whose is the possessive form of who.

Whose house is that? (the house belonging to whom)
He is the one whose wife works at the bank. (the wife of whom)

© The English Department 1999