Apostrophe

The apostrophe (’) is a punctuation mark used in writing. It is a diacritic (a mark used with letters).

In English, it has two jobs:

• To show where one or more letters have been left out (as in the abbreviation (contraction) of do not to don't).
• To show the possessive case (as in the cat’s whiskers).

Examples

Its versus it's

The most common grammatical mistake in written English is to put it's where its is correct. Its: a possessive adjective and pronoun of the personal pronoun it.

• The cat chased its tail. Correct.
• The tyre lost it's grip. Wrong.

It's: a contraction of the verbal phrase It is or It has.

• It's mine. Correct; check: It is mine.
• It's been here. Correct; check: It has been here.
• The cat chased it's tail. Wrong; cannot be expanded to It is.

The same applies to yours, theirs and ours because these are also possessive adjectives of personal pronouns.

• The colour is ours.
• That book is hers (or his).
• Theirs was the responsibility.

Possession

Apostropes are also used to show something belongs to someone (or something). Again, correct uses can be expanded:

• Mike's car. Correct: the car that belongs to Mike.
• The dog's ball. Correct: the ball that belongs to the dog.
• Those dog's are large. Wrong: cannot be expanded. Here "dogs" is a plural word.

The intrusive apostrophe

Comes in plurals which don't (do not) need it. Do not put an apostrophe in word ending in s, such as a plural. Put an apostrophe, or 's, at the end of the word instead.

• Mrs. Jones' hat or Mrs. Jones's hat. Both correct.
• Both of my parents' birthdays. Correct.

• CD's and DVD's: wrong
• Apple's and pear's: wrong

Writing dialogue or titles

Apostrophes are also used when other words are shortened, as in slang:

• Go get 'em tiger! or Li'l Bow Bow.

This is just a version of the abbreviation function.