Apostrophe Usage Crib Sheet

Apostrophes are used in THREE ways:

1.  Apostrophe + s = OWNERSHIP or possession with ordinary nouns:
cat's, Peter's, George's, dog's (meaning "belonging to one dog") dogs' (meaning "belonging to several dogs")

2.  Apostrophes show a dropped letter in CONTRACTIONS:
it's = it is, you're = "you are", that's = "that is", couldn't = "could not"

3.  Single quotes are used inside of NESTED QUOTES to show remarks heard secondhand:
John said, "Mary said to me yesterday, 'I don't want kids.'"

Apostrophes are NOT used for:

1.  Possessive PRONOUNS (the idea of possession is built-in):
its scent, my house, your lollipop, his computer, their reservation; the floor is yours

2.  PLURAL nouns (just add -s or -es, no apostrophe):
dogs, cats, the Joneses, butterflies, CDs, 1980s, PhDs

Tricky situations with possessive nouns (NOT pronouns):

1.   If a noun already ends in s, to make it possessive, just add ' :
three days' work, the bus' wheels, Massachussetts' governor

2.  EXCEPT... if a noun is a singular proper name ending in s -- that is, it's capitalized -- add 's :
John Edwards's candidacy

3.   With two or more nouns, add an 's to the last noun only if they all own the thing in common:
Bill and Ted's Excellent Adventure

4.   With two or more nouns, add an 's to each noun if they own things separately:
Bill's and Ted's underwear (each has his own underwear)

From: The Care and Feeding of Apostrophes by E. Brundige

URL: http://www.squidoo.com/apostrophe