Aposthrophe

Where do we use aposthrophe ?

•  to form possessives of nouns
• to show the omission of letters
• to indicate certain plurals of lowercase letters

To check if you need possessives, turn the phrase around and change it to "of, the,..." phrase. For instance;

the boy's hat = the hat of the boy
three days' journey = journey of three days

If the noun after "of" is a building, an object, or a piece of furniture, then no apostrophe is needed!

room of the hotel = hotel room
door of the car = car door
leg of the table = table leg

Apostrophes are used in contractions. For example,

don't = do not
I'm = I am
he'll = he will
who's = who is
shouldn't = should not
didn't = did not
could've= could have (NOT "could of"!)
'60 = 1960

You musn`t use aposthrophes for personal pronouns, the relative pronoun who, or for noun plurals.

wrong: his' book
correct: his book
correct: one's book
correct: anybody's book

wrong: Who's dog is this?
correct: Whose dog is this?

wrong: The group made it's decision.
correct: The group made its decision.