When creating possessive form nouns there are 8 simple rules:
1. If a singular noun does not end in s, add 's.
- The delivery boy's truck was blocking the driveway.
- Bob Dole's concession speech was stoic and dignified.
- The student's attempts to solve the problem were rewarded
2. If a singular common noun ends in s, add 's- unless the next word begins with s. If the next word begins with s, add an apostrophe only. (This includes words with s and sh sounds.)
- The boss's temper was legendary among his employees.
- The boss' sister was even meaner.
- The witness's version of the story has several inconsistencies.
- The witness' story did not match the events recorded on tape.
3. If a singular proper noun ends in s, add an apostrophe.
- Chris' exam scores were higher than any other students.
4. If a noun is plural in form and ends in an s, add an apostrophe only, even if the intended meaning of the word is singular (such as mathematics and measles.)
- The instructor asked us to analyze ten poems' meanings.
- The dog catcher had to check all of the dogs' tags.
- It is hard to endure the Marine Corps' style of discipline.
5. If a plural noun does not end in s, add 's.
- Many activists in Oregon are concerned with children's rights.
- Everyone was disappointed with the American media's coverage of the Olympics in Atlanta.
6. If there is joint possession, use the correct possessive for only the possessive closest to the noun.
- Clinton and Gore's campaign was successful.
- She was worried about her mother and father's marriage.
- Beavis and Butthead's appeal is absolutely lost on me.
7. If there is a separate possession of the same noun, use the correct possessive form for each word.
- The owner's and the boss's excuses were equally false.
- The dog's and the cats' owners were in school when the fire broke out.
8. In a compound construction, use the correct possessive form for the word closest to the noun. Avoid possessives with compound plurals.
- My father-in-law's BMW is really fun to drive.
- The forest ranger's truck is painted an ugly shade of green.
- Your neighborhood letter carrier's job is more difficult than you imagine.