Grammar Help — Words — Apostrophes

The apostrophe is used in contractions and often (but not always) to indicate the possessive case.

1. Contractions

The apostrophe is used to indicate where some letters or portions of words have been left out especially when two words are joined. Note: the apostrophe represents the missing letters, not the missing space.

It's or its	It's: Meaning: it is Example: It's a boy! Its: Meaning possessive case of it Example: It went to its home. Common Error: Using "it's" for possession: This is an exception to the rule for use of apostrophes. It's a very common error. The bird is in its nest. It's a nice nest. It's made out of sticks. Note: Its' is NEVER used.
He's	Meaning: he is (used for 'he has' informally, not usually appropriate for formal writing)
n't Can't, Don't, Won't, Isn't, couldn't, wouldn't,shouldn't	Note: all the words joined with 'not' end in "n't ". The apostrophe represents the elimination of the "o" and we don't need anything to represent the elimination of the space between the words.
Their	refers to something which belongs to them Example: We went in their car.
Theirs	refers to something which belongs to them Example: that car is theirs Note: No apostrophe for the personal pronouns
There's	Meaning: There is Example: There's the bus! Common Error: Mistaking there's and theirs
They're	Meaning: they are Example: They're over there in their car. Common Error: Mistaking they're, there and their. See example for correct usage of all three.
Who, Whom	Who — used as the subject of a sentence Example: Who threw the ball? Whom — used as the object of a sentence Example: To whom was the ball thrown? Use 'who' when it's the subject of a clause when even though the clause is the object of the sentence. I spoke to the principal, who is also the gym teacher.
Who's	Meaning: Who is Common Error: Whose, refers to possession Example: Who's there? The boy whose parents died.
Your	When something belongs to you Example: It's your car.
Yours	When something belongs to you Example: Take it, it's yours Note: personal prounoun never take an apostrophe
You're	Meaning: you are Example: You're going to love this. Common Error: Using "you're" when you should use "your" for the second person possessive. Remember, the apostrophe reminds you that there's something left out.

2. Possessive

An apostrophe is used to indicate the possessive case.

An apostrophe before the s is used to indicate possessive case	Frank's dog. Frank's dog's bone. Exceptions: It's = it is so use "its" for possessive. Example: It's Frank's dog. Frank's dog chews its bone.
An apostrophe is used after the s only when the noun ends in s and the addition of another s is awkward.	Example: The Smith's house is beside the Jones' house Example: It's the Raiders' ball on the 10 yard line! Example: I took a big bite out of the octopus' tentacle and he didn't like it! Note: An apostrophe is never used after the s in its.