Misuse of the Apostrophe

The basic rule is quite simple: use the apostrophe to indicate possession, not a plural. The exceptions to the rule may seem confusing: hers has no apostrophe, and it’s is not possessive. Nevertheless, with some attention, you can learn the rules and the exceptions.

Possessives

Form the possessive case of a singular noun by adding ’s (even if the word ends in s).

Examples: Hammurabi’s code, Dickens’s last novel, James’s cello

Form the possessive case of a plural noun by adding an apostrophe after the final letter if it is an s or by adding ’s if the final letter is not an s.

Examples: the students’ books, the children’s toys

Remember: the apostrophe never designates the plural form of a noun.

Compare the following correct sentences: 

The student’s book was missing. (singular possessive) 

Several students’ books were missing. (plural possessive) 

The students searched for their missing books. (plural)

Possessive Pronouns, such as yours, hers, its, and ours, take no apostrophe.

Example: The decision is yours.

Indefinite Pronouns, such as anyone, everybody, no one, and somebody, use the singular possessive form.

Example: Somebody’s dog stayed in our room last night.

Contractions

The apostrophe is used to mark omitted letters in contractions.

Note that contractions are often considered too informal for academic writing.

Avoid the Dreadful It’s/Its Confusion:

It’s is a contraction for “it is.” It’s is never a possessive.
Its is the possessive for “it.”

As Strunk and White remind us in The Elements of Style (4th ed.), “It’s a wise dog that scratches its own fleas” (1).

See Sin No. 5