Rhetoric and Composition/Apostrophes

Use

Apostrophes are used to indicate possession and in contractions.

Add an "'s" when the noun does not end in an "s" (driver's) or when the noun is singular and ends in an "s" (Lois's).

However, if the pronunciation of a word would be awkward with the "s" added, it is acceptable not to use the extra "s".

If the noun is plural and ends in "s", you don't need to add an apostrophe (diplomas' instead of diploma's).

Joint Possession

If there is a compound noun, add the possessive apostrophe to the last noun.

Example: I went to see Anthony and George's new apartment. (The apartment belongs to both Anthony and George.)

If the compound noun indicates individual possession, add the apostrophe to both nouns.

Example: Mary's and Brian's sense of style was quite different. (Mary and Brian have individual senses of style.)

Compound Nouns

If a compound noun uses dashes, place the apostrophe after the last nouns.

Example: My brother-in-law's house

Do not use apostrophes in nouns that are not possessive. Example: Some parent's are more strict than mine. (Apostrophe is not necessary)
Do not use an apostrophe in possessive pronouns such as its, whose, his, hers, ours, yours, and theirs.