Student's guide to writing college papers, Fourth edition - Kate L. Turabian 2010

Possessives
Spelling: plurals, possessives, and hyphenation
Style

21.3.1 The General Rules

Singular Nouns

For most singular nouns, including abbreviations, add an apostrophe and s, even if the word ends in s, x, or z.

the argument's effects Jones's paper Diaz's paper JFK's speech

Plural Nouns Ending in s

For regular plural nouns, add an apostrophe without an additional s.

the arguments' effects politicians' votes

the Davises' house the Cavs' lineup

Plural Nouns Not Ending in s

For irregular plurals that do not end in s, add both an apostrophe and s.

the children's hour the mice's nest

alumni's donations the men's room

21.3.2 Special Cases

Exceptions for Singular Nouns Ending in s

For collective nouns that end in s but are treated as singular nouns, add an apostrophe without an additional s.

politics' true meaning the United States' role

Nouns for Inanimate Objects

In most cases, you should not create possessives for inanimate objects.

NOT: the house's door the hammer's handle the shirt's color

Singular Compound Nouns

Add an apostrophe and an s to the last word in the compound.

bookkeeper's records handyman's tools district attorney's case

sister-in-law's children attorney general's decision

Plural Compound Nouns

For compounds composed of two nouns, form the possessive based on the last word in the compound.

bookkeepers' records handymen's tools district attorneys' cases

Avoid possessive forms for compounds with a noun followed by an adjective or prepositional phrase; rephrase instead.

NOT: sisters-in-law's children BUT: the children of the sisters-in-law

NOT: attorneys' general decisions BUT: the decisions of the attorneys general

Multiple Nouns

To indicate that two or more nouns in a series each posses something separately, make all the nouns possessive.

New York's and Chicago's teams historians' and economists' methods

To indicate that two or more entities possess something jointly, make only the last noun possessive.

Minneapolis and St. Paul's team historians and economists' data

Terms in Italics

Add an apostrophe and an s, both in roman type.

the Atlantic Monthly's editor the Chicago Tribune's readers

Terms in Quotation Marks

Avoid possessive forms for terms in quotation marks; rephrase instead.

NOT: the “Ode on a Grecian Urn”'s admirers

BUT: admirers of the “Ode on a Grecian Urn”