This has come up several times over the past week, so I thought I would post a few refresher rules on possessive case.
Possessive Case, Nouns
When the noun does not end in an s, add and apostrophe and an s.
When the noun ends in an s, add only an apostrophe.
This rule does not distinguish between singular and plural nouns. This rule also applies to nouns used as possessive adjectives (five dollars’ worth of gas).
Possessive Case, Pronouns
Personal pronouns do not take an apostrophe. These nouns include his, hers, its, ours, yours, theirs and whose.
Indefinite pronouns take an apostrophe and an s.
Everybody’s favorite story
Possessive Case, Compounds
In hyphenated words, names of organizations consisting of more than one word, and words indicating joint possession, only the last word takes the possessive form. The form of the possessive follows the rules for nouns in the possessive case.
* Ex-husband’s habits (hyphenated)
* Smith and Wesson’s finest model (organization, singular)
* Parker Brothers’ product line (organization, plural)
* Romy and Michelle’s High School Reunion (joint possession)
Exception: In the case of joint possession, when the first part of the pair is a noun and the final part is a pronoun in the possessive case, then the noun follows the rule for nouns in the possessive case.
* Robert’s and my anniversary
But note: this only applies to joint possession, that is, things owned in common. When two or more people possess something individually, each of their names is possessive in form.
* Shaq’s and Kobe’s championship rings (Each player has his own ring. They do not share a single ring in joint possession.)
This is just one of those things you have to learn if you want to be one of the cool kids.