Like the comma, the apostrophe wields amazing power. The talented little dot-and-tail combination (though written at the top of the line, not at the bottom like the comma) can change pronouns to verbs, tell you who owns what, replace a small handful of letters, and make plurals. It comes from the Greek words meaning to turn from or omission.
After commas, apostrophes seem to be the most misused punctuation mark; grammar vigilantes have their work cut out for them.
(Photo source: iwastesomuchtime.com)
Possessive Case of Nouns
With the addition of ’s (or sometimes just the apostrophe), a noun can change from a plain old person, place or thing to a person, place or thing that owns something.
— If the noun doesn’t end with an s, add ’s to the end of the noun.
Example: This is Mary and a dog. The dog is Mary’s; Mary is not the dog’s.
— If the noun ends with an s, add ’s OR add just the apostrophe to the end of the noun, depending on style guide preference.
Examples: Where is Jess’ book bag?
My parents’ house is a lovely old one.
— If you have a compound noun, change only the last one to the possessive.
Example: Mike and Amanda’s new loft apartment is really neat.
— If the possessor is a building, an object, or a piece of furniture, then you don’t need to add an apostrophe to show possession.
Example: The hotel’s room –> the hotel room
Contractions and Omissions
Apostrophes can show an omission of letters, whether as part of a contraction or when showing dialect or accent.
Examples: I’m = I am
Can’t = can not, cannot
Where’s = where is
Apostrophes and Possessive Pronouns
Possessive pronouns don’t require an apostrophe.
Examples: That book is his’. —> That book is his.
No, it’s mine’s! —> No, it’s mine!
The cat washed it’s face. = The cat washed its face. (It’s is a contraction of it is, not a possessive pronoun.)
!! Exception: Indefinite pronouns can be made possessive with an apostrophe.
Indefinite pronouns can be made possessive with the use of ’s. Indefinite pronouns are words like someone, other, and any.
Examples : One – one’s
Is this anyone’s backpack lying here on the ground?
Forming Plurals of Lower- and Upper-case Letters
When you’re trying to describe plural letters, use ’s after the letter so that it’s clearly identified as a letter, not a word. If, for instance, you write is instead of i’s, your reader will get confused between the verb and the letter i.
Example: Mind your p’s and q’s, my dear!