Using Apostrophes to Show Possession

Apostrophes can be used to show who owns or possesses something. 

For Nouns Not Ending in -s

The basic rule is that to indicate possession, add an apostrophe followed by an "s" to the end of the word.

• The car belonging to the driver = the driver's car.
• The sandwich belonging to Lois = Lois's sandwich.
• Hats belonging to children = children's hats.

For Nouns Ending in -s

However, if the word already ends with "s," just use the apostrophe with no added "s." For example:

• The house belonging to Ms. Peters = Ms. Peters' house. (Even though Ms. Peters is singular. )

The same holds true for plural nouns, if their plural ends in "s." Just use an apostrophe for these!

• Three cats' toys are on the floor.
• The two ships' lights shone through the dark.

For More Than One Noun

In sentences where two individuals own one thing jointly, add the possessive apostrophe to the last noun. If, however, two individuals possess two separate things, add the apostrophe to both nouns. For example:

• Joint: I went to see Anthony and Anders' new apartment. (The apartment belongs to both Anthony and Anders.)
• Individual: Anders' and Anthony's senses of style were quite different. (Anders and Anthony have individual senses of style.)

For Compound Nouns

In cases of compound nouns composed of more than one word, place the apostrophe after the last noun. For example:

• Dashes: My brother-in-law's house is down the block.
• Multi-word: The Minister for Justice's intervention was required.
• Plural compound: All my brothers-in-law's wives are my sisters.

For Words Ending in Punctuation

If the word or compound includes, or even ends with, a punctuation mark, an apostrophe and an "s" are still added in the usual way. For example:

• Westward Ho!'s railway station
• Louis C.K.'s HBO special

For Words Ending in -'s

If an original apostrophe, or apostrophe with s, is already included at the end of a noun, it is left by itself to perform double duty. For example:

• Our employees are better paid than McDonald's employees.
• Standard & Poor's indexes are widely used.

The fixed, non-possessive forms of McDonald's and Standard & Poor's already include possessive apostrophes.

Don't Use Apostrophes For ...

Nouns that are not possessive. For example:

• Incorrect: Some parent's are more strict than mine.

Possessive pronouns such as its, whose, his, hers, ours, yours, and theirs. These are the only words that are able to be possessive without apostrophes. For example:

• Incorrect: That parakeet is her's.

Using Apostrophes to Form Contractions

In addition to serving as a marker for possession, apostrophes are also commonly used to indicate omitted characters. For example:

• can't (from cannot)
• it's (from it has or it is)
• you've (from you have)
• gov't (from government)
• '70s, (from 1970s)
• 'bout (from about)

An apostrophe is also sometimes used when the normal form of an inflection seems awkward or unnatural. For example:

• K.O.'d rather than K.O.ed (where K.O. is used as a verb meaning "to knock out")

Using Apostrophes to Form Plurals

Apostrophes are sometimes used to form plurals for abbreviations, acronyms, and symbols where adding just s as opposed to 's may leave things ambiguous or inelegant. For example, when you are pluralizing a single letter:

• All of your sentences end with a's. (As opposed to "All of your sentences end with as.")
• She tops all of her i's with hearts. (As opposed to "She tops all of her is with hearts.")

In such cases where there is little or no chance of misreading, however, it is generally preferable to omit the apostrophe. For example:

• He scored three 8s for his floor routine. (As opposed to "three 8's.")
• She holds two MAs, both from Princeton. (As opposed to "two MA's.")