A Practical and Authoritative Guide to Contemporary English. 1996.
8. Word Formation
b. Forming Possessives
IN English the possessive case is used to show not only simple possession but also a variety of other relationships between the noun marked for possession and the noun that follows:
Johns car the senators aide
(possession or belonging)
the tides ebbing, Amys presentation
(subject of an action)
the companys owners, the heros betrayal
(object of an action)
learners dictionary, a womens college
(description or type)
my fathers gentleness, the characters greed
(attribute)
the birds wing, the books cover
(a constituent part)
Beethovens symphonies, grandmothers letter
(origin)
a days journey, an arms length
(measure or amount)
1
Following are the few basic rules for forming the possessive case in English.
2
The possessive case of a singular noun is formed by adding -s: ones home, by days end, our familys pet, the witnesss testimony, a foxs habitat, the knifes edge. Note that although some people use just the apostrophe after singular nouns ending in s (the witness testimony, Burns poetry), the -s is generally preferred because it more accurately reflects the modern pronunciation of these forms. However, in a few cases where the -s is not pronounced, it is usual to add just the apostrophe: for righteousness (appearance) sake.
3
The possessive case of a plural noun ending in -s is formed by adding just an apostrophe: the doctors recommendations, the glasses rims, the flies buzzing noises. However, when the plural noun does not end in -s, form the possessive by adding -s: childrens clothes.
4
The possessive case of most proper nouns is formed according to the rules for common nouns: (singular) Eliots novels, Yeatss poetry, Dostoyevskys biography, Velázquezs paintings; (plural) the McCarthys and the Williamses parties, the Schwartzes trip. By convention, however, certain proper nouns ending in s form the possessive by adding just the apostrophe since adding -s would make the pronunciation difficult or awkward: Jesus teachings, Moses children, Achilles heel Hercules strength, Ramses reign, Xerxes conquest.
5
For compound names or titles that form short phrases, add the -s or apostrophe to the final element: the King of Belgiums birthday, Saint Francis of Assisis life, the governor of New Yorks speech. Long phrases such as the man we met on the trains sister should be avoided in writing. Reword them using of: the sister of the man we met on the train.
6
When two or more people or things possess something jointly, add the -s or apostrophe to the last element only: Martha and Dans house. However, when two or more people or things possess something separately, add the -s or apostrophe to each element: the Smiths and the Joneses houses are for sale.