http://www.northland.cc.mn.us/...Apostrophe%20Rules.htm
Apostrophe Rules
"The Apostrophe Protection Society was started in 2001 by John Richards, now its Chairman, with the specific aim of preserving the correct use of this currently much abused punctuation mark in all forms of text written in the English language."o
The Society has its work cut out for it, not because the apostrophe is so difficult to use, but because people simply forget to use it. The rules are actually quite simple, and when writers are reminded of them, most understand why and how this abused punctuation mark is needed.
1. Use an apostrophe s ('s) to indicate possession in singular nouns. Simply put 's after any singular noun when that noun is to show possession.
Ex. A: The cat's purr can put me to sleep when I feel anxious.
Ex. B: His personality traits indicated that he was not free from writer's block.
Ex. C: George left his mother-in-law's briefcase on the bus again.
Ex. D: No one agreed with Gladys's argument about the need for more water fountains in the hallways.
2. Use an s apostrophe (s') to indicate possession in plural nouns ending in s.
Ex. A: She removed all her blankets' tags before she ever used them on beds.
Ex. B: Since the baby carriages' wheels have been found defective, all Care-for-Me products have been recalled.
Ex. C: Steve Bergdal, the police commissioners' secretary, notified all officers that they would be issued tasers.
3. Use an apostrophe s ('s) to indicate possession in plurals that do not end in s.
Ex. A: The men's room did not have a functioning sink.
Ex. B: Children's playground equipment should be sturdy enough to handle a 250 pound child.
Ex. C: Clare left her brothers-in-law's gifts with her sisters.
4. Use an apostrophe to indicate a missing letter, as in contractions or colloquialisms.
Ex. A: Simply don't leave the house without checking for polar bear alerts.
Ex. B: She's going to be upset when she discovers that her secretary didn't leave his phone number with the receptionist.
Ex. D: Sylvester told his cousins, "Too much book larnin' is dangerous."
Caution: Do not use an apostrophe to write plurals.
Ex. A:
Incorrect: All CD's offered at a 5% interest rate.
Correct: All CDs offered at a 5% interest rate.
Ex. B:
Incorrect: African-American's have become as economically successful as European-American's.
Correct: African-Americans have become as economically successful as European-Americans.
Ex. C:
Incorrect: He received all D's on his report card because he failed to attend classes.
Correct: He received all Ds on his report card because he failed to attend classes.
Ex. D:
Incorrect: The 1960's was an era of change and good fortune.
Correct: The 1960s was an era of change and good fortune.
Ex. E:
Incorrect: There were more Jason's in the class than Jude's.
Correct: There were more Jasons in the class than Judes.
Ex. F:
Incorrect: The Harvey's left their house in the care of the Klingenfelder's.
Correct: The Harveys left their house in the care of the Klingenfelders.