Noun Possessives

To determine whether you need to add -s, follow these steps:
1. Write down the possessor or possessors. Examples:
Sarah |
the girls |
women |
Jesus |
Arkansas |
2. Put an apostrophe after the possessor or possessors. Examples:
Sarah' |
the girls' |
women' |
Jesus' |
Arkansas' |
3. Add the noun that is being possessed after the word, and pronounce the two words aloud to find out whether you add an additional "s" sound to the possessor when you say it. If you do, add an "s" after the apostrophe.
Examples:
Sarah'__sweater |
Sarah's sweater |
the girls'__ locker room |
the girls' locker room |
women'__ health |
women's health |
Jesus'__ sandals |
Jesus's sandals or Jesus' sandals |
Arkansas'__ rivers |
Arkansas's rivers |
As you can see in these examples, the use of an apostrophe is pronunciation driven and thus individualized, not determined by hard and fast rules in all cases.