The Apostrophe

The apostrophe has three uses:

to form possessives of nouns

to show the omission of
letters

to indicate certain plurals
of lowercase letters

Forming Possessives of Nouns

To see if you need to make a possessive, turn the phrase
around and make it an "of the..." phrase. For example:

the boy's hat = the hat of the boy

three days' journey = journey of three days

If the noun after "of" is a building, an object, or a piece of
furniture, then no apostrophe is needed!

room of the hotel = hotel room

door of the car = car door

leg of the table = table leg

Once you've determined whether you need to make a possessive, follow these
rules to create one.

add 's to the singular form of the word (even
if it ends in -s):

the owner's car

James's hat

add 's to the plural forms that do not end in
-s:

the children's game

the geese's honking

add ' to the end of plural nouns that end in
-s:

houses' roofs

three friends' letters

add 's to the end of compound words:

my brother-in-law's money

add 's to the last noun to show joint
possession of an object:

Todd and Anne's apartment

Showing omission of letters

Apostrophes are used in contractions. A contraction is a word (or set of
numbers) in which one or more letters (or numbers) have been omitted. The
apostrophe shows this omission. Contractions are common in speaking and in
informal writing. To use an apostrophe to create a contraction, place an
apostrophe where the omitted letter(s) would go. Here are some examples:

don't = do
not

I'm = I am

he'll = he will

who's = who is

shouldn't = should not

didn't = did not

could've= could have (NOT "could of"!)

'60 = 1960

Forming plurals of lowercase letters

Apostrophes are used to form plurals of letters that appear in lowercase;
here the rule appears to be more typographical than grammatical, e.g.
"three ps" versus "three p's." To form the plural of a lowercase letter, place 's after the letter. There is
no need for apostrophes indicating a plural on capitalized letters, numbers,
and symbols (though keep in mind that some editors, teachers, and professors
still prefer them). Here are some examples:

p's
and q's = a phrase indicating politeness, possibly
from "mind your pleases and thankyous"?

Nita's mother constantly stressed minding one's p's and q's.

three Macintosh G4s =
three of the Macintosh model G4

There are two G4s currently used in the writing classroom.

many & s = many
ampersands

That printed page has too many & s on it.

the 1960s = the years in
decade from 1960 to 1969

The 1960s were a time of great social unrest.

Don't use apostrophes for possessive pronouns or for noun plurals.

Apostrophes should not be used with possessive pronouns because possessive
pronouns already show possession — they don't need an apostrophe. His,
her, its, my, yours, ours are all possessive pronouns. Here are some examples:

wrong: his'
book

correct: his book

wrong: The group made it's decision.

correct: The group made its decision.

(Note: Its and it's are not the same thing. It's is
a contraction for "it is" and its is a
possessive pronoun meaning "belonging to it." It's raining out= it is
raining out. A simple way to remember this rule is the fact that you don't use
an apostrophe for the possessives his or hers, so don't do it with its!)

wrong: a friend of yours'

correct: a friend of yours

wrong: She waited for three hours' to get her ticket.

correct: She waited for three hours to get her ticket.

Proofreading for apostrophes

A good time to proofread is when you have finished writing the paper. Try
the following strategies to proofread for apostrophes:

If you tend to leave out
apostrophes, check every word that ends in -s or -es
to see if it needs an apostrophe.

If you put in too many
apostrophes, check every apostrophe to see if you can justify it with a
rule for using apostrophes.

Based on the rules for using apostrophes, choose the correct version of the
words from the drop down list to complete the sentences.

Apostrophe
Exercises #1
http://owl.english.purdue.edu/handouts/interact/g_apostEX1.html

Apostrophe
Exercises #2
http://owl.english.purdue.edu/handouts/interact/g_apostEX2.html