Apostrophe

1. Use an apostrophe in possessive forms:

• the ball of the boy → the boy's ball
• Tara's sister
• my friend's mother
• New York's nightmare scenario
• the moon's phases

2. Use an apostrophe in contracted forms (the apostrophe shows that letters have been left out):

• cannot → can't
• they have → they've
• I would (or I had) → I'd
• it is (or it has) → it's
• who is → who's

Certain words are sometimes written with an apostrophe (to show that they are really a shortened form of the original, longer word):

• influenza → 'flu (or flu)
• telephone → 'phone (or phone)

Some people use an apostrophe when the first two figures of a year are left out:

• 1948 → '48

3. You can use an apostrophe to show the plural of letters and numbers:

• You should dot your i's and cross your t's.
• Do you like music from the 1950's?

You can use an apostrophe to show a plural form for words that are not normally plural:

• Your plan is good, even if there are lots of if's and but's in it.