apostrophes

Use to indicate possession (the doctor’s stethoscope, the nurse’s stethoscope), or omitted letters or figures (don’t, ’50).

Use with degree names (bachelor’s degree, master’s degree).

Exception: associate degree has no apostrophe.

In alumni graduation years and other instances to indicate missing text, make sure apostrophes face toward the missing characters (’50s, grab ’n go, ’til).

Do not use to indicate plurals in numerals or acronyms (1990s, HMOs, RNs).

Use only an apostrophe with singular proper names ending in “s” (Achilles’ heel, Agnes’ book, Descartes’ theories, Hercules’ labors, Texas’ schools, Tennessee Williams’ plays).

Use an apostrophe and an “s” with singular common nouns ending in “s” (the hostess’s invitation, the witness’s answer).

To indicate ownership, use a possessive form after only the last word if ownership is joint: Fred and Sylvia’s apartment (indicating that they share the apartment). Use a possessive form after both words if the objects are individually owned: Fred’s and Sylvia’s books (indicating that some books in question belong to Fred, others to Sylvia).

Always use ‘s if the word does not end in the letter “s,” even for words that end with an “s” sound (Butz’s policies, the fox’s den, the justice’s verdict, Marx’s theories, the prince’s life, Xerox’s profits). The following exceptions to the general rule for words not ending in s apply to words that end in an s sound and are followed by a word that begins with s: for appearance’ sake, for conscience’ sake. Use “‘s” otherwise (the appearance’s cost, my conscience’s voice).

Do not add an apostrophe to a word ending in s when it is used primarily in a descriptive sense (citizens band radio, a Cincinnati Reds infielder, a teachers college, a writers guide). An ‘s is required, however, when a term involves a plural word that does not end in s: (a children’s hospital, a people’s republic).

Follow the rules above in composing the possessive form of words that occur in quasi-possessive phrases (a day’s pay, two weeks’ vacation, three days’ work, your money’s worth). Frequently, however, a hyphenated form is clearer (a two-week vacation, a three-day job). See hyphens.