Contractions (e.g., let’s, don’t, couldn’t, it’s, she’s) have a bad reputation. Many argue that they have no place at all in formal writing. You should, of course, observe your publisher’s or instructor’s requirements. An absolute avoidance of contractions, however, is likely to make your writing appear stilted and unwelcoming.
If you are unsure where to insert the apostrophe when forming a contraction, consult a good dictionary. Avoid the most common contraction–apostrophe error: the contraction of it is is it’s; without the apostrophe, its is the possessive form of it.
Example: It’s often said that every dog has its day.
In informal writing, it is acceptable to indicate a year with only the last two digits preceded by an apostrophe (e.g., the class of ’85, pop music from the ’80s).
The apostrophe is seldom used to form a plural noun.
Incorrect: Since the 1980’s, the Thomas’s, both of whom have multiple PhD’s, sell old book’s and magazine’s at the fair on Saturday’s and Sunday’s.
Correct: Since the 1980s, the Thomases, both of whom have multiple PhDs, sell old books and magazines at the fair on Saturdays and Sundays.
The rare exception to the rule is when certain abbreviations, letters, or words are used as nouns, as in the following examples. Unless the apostrophe is needed to avoid misreading or confusion, omit it.
He received four A’s and two B’s.
We hired three M.D.’s and two D.O.’s.
Be sure to cross your t’s and dot your i’s.
Do we have more yes’s than no’s?
For this last example, the trend is to instead write yeses and noes.
The formation of possessives is treated in different ways by different authorities. The rules below are based on The Chicago Manual of Style, 16th edition, and are appropriate for most writing. Associated Press style, used by most newspapers, is slightly different. See the essay on style for more information.
The general rule is that the possessive of a singular noun is formed by adding an apostrophe and s, whether the singular noun ends in s or not.
the lawyer’s fee
the child’s toy
Xerox’s sales manager
Tom Jones’s first album
Aeschylus’s finest drama
a week's vacation
The possessive of a plural noun is formed by adding only an apostrophe when the noun ends in s, and by adding both an apostrophe and s when it ends in a letter other than s.
excessive lawyers’ fees
the twins’ parents
the student teachers’ supervisor
the Smiths’ vacation house
the boys’ baseball team
the alumni’s fundraising
someone with twelve years’ experience
Use only an apostrophe for places or names that are singular but have a final word in plural form and ending with an s.
Beverly Hills’ current mayor
the United States’ lingering debt problem
Cisco Systems’ CEO
Nouns that end in an s sound take only an apostrophe when they are followed by sake.
for goodness’ sake
for conscience’ sake
A proper noun that is already in possessive form is left as is.
T.G.I. Friday’s menu was recently changed.
Joint possession is indicated by a single apostrophe.
Robert Smith and Rebecca Green’s psychology textbook. (they coauthored the book)
Stanley and Scarlett’s house. (they share the house)
Individual possession is indicated by apostrophes for each possessor.
France’s and Italy’s domestic policies are diverging.
Chris’s and John’s houses were designed by the same architect.
Correct but awkward: St. Patrick’s Cathedral’s Fifth Avenue entrance.
Better: The Fifth Avenue entrance for St. Patrick’s Cathedral.
The apostrophe should never be separated from the word to which it attaches by adjacent punctuation.
Correct: The house on the left is the Smiths’, but the house at the end of the street is the Whites’.
Incorrect: The house on the left is the Smiths,’ but the house at the end of the street is the Whites.’