1. When we want to show that someone owns something, we use possessive nouns.
- The fingers of Joy = Joy's fingers
- The hands of Emily = Emily's hands
2. To make a noun possessive, usually add an apostrophe and an s
- Alma -- Alma's dog
- dog -- the dog's tail
- James -- James's mustache
3. Most of the exceptions to this rule are old-fashioned or historical names:
- Jesus' parables
- Moses' tablets
- Achilles' heel
4. If two people own the same thing, use an apostrophe and s for only the second person.
- Jon and Alma's marriage (they share one marriage)
- Bea and Gabby's mother (they share one mother)
5. If the two people don't own the same thing, use an apostrophe and s for both people.
- Bea's and Gabby's toys. (they don't share the same toys)
- Jon's and Paolo's toes. (they don't share the same toes)
6. If the plural ends in s (for example, girls) just add an apostrophe. If the plural does not end in s (for example, men) add an apostrophe and an s.
- the boy's sweater -- the boys' sweaters
- my sister's van -- my sisters' van
- my boss's key -- my bosses' keys
- the man's coat -- the men's coats
- the child's book -- the children's books
7. Inanimate objects usually don't own things, but some possessives are fine.
- one week's vacation; two weeks' vacation
- one table's leg; two tables' legs
- one peso's worth; two pesos' worth
8. What about the example the table's leg? It's fine, but in formal writing such as in Task 2 of the IELTS writing module, it should be the table leg or the leg of the table. The same is true with this example.
- ALL RIGHT: my car's tire
- BETTER: my car tire (I own the tire - the car doesn't own it.)
- ALSO GOOD: the tire on my car
9. Proper nouns (people names) that end in s can be confusing.
- Mr. and Mrs. Santos have a new house.
- The Santoses have a new house.
- Mr Santos's house is new.
- The Santoses' house is new.
Attribution to Rebecca Elliot for her book Painless Grammar (c) 2006, 1997
Other noun tips:
16 Tips on How to Capitalize Nouns (Nouns, Part 1 of 3)
9 Tips about Possessive Nouns (Nouns, Part 2 of 3)
14 Tips on Making Plural Nouns (Nouns, Part 3 of 3)