Today, I got a question about possessives. Hooray! I love grammar questions! And not only that, but I now have the opportunity to quote at length from my very own book. ("I'm so vain, I probably think this possessives question is about me, I'm so vaaaaaainnn.....") Here now is the relevant excerpt from Ultimate Style:
For most words, simply add an apostrophe and s.
- The men's locker room is dirtier than the women's.
Add an apostrophe plus s to the end of singular words that end in s. (Note: this is a style preference. Some grammar books will tell you to add just an apostrophe [no s] to singular words that end in s. That's okay, too!]
- Yolanda read Charles Dickens's A Christmas Carol.
- Massachusetts's baseball team infuriated Boston fans for years.
- The boss's tone seemed off.
We at SparkNotes prefer to be guided by pronunciation: since we hear an uhz sound at the end of class in class's disappointment, we write the s.
Add an apostrophe to the end of plural words that end in s.
- We're jealous of the Joneses' new lawn mower.
- The stars' light illuminated the path through the woods.
If two words are a unit, you need only one apostrophe plus s.
- Peanut butter and jelly's main appeal is its combination of saltiness and sweetness.
- My mother and father's house smells like orchids.
Be careful, though—sometimes two words appear to be a unit but are not. In those cases, each word gets an apostrophe plus s.
- Cynthia always sends flowers on her mother's and father's birthdays.
- Rand's and Machievelli's philosophies inspired the cruel man.