You use apostrophes for two purposes.  The first is to concatenate words, and the second is to express possession.  In this post, I discuss the rules for using apostrophes in these two instances, along with a couple of notable exceptions.

Using Apostrophes for Contraction

Use an apostrophe (‘) for word contraction.  For example:

Do not becomes don’t.
Is not becomes isn’t.
I have becomes I’ve.

Notice how the personal pronoun “I” remains capitalized, even in contracted form.

Using an Apostrophe and s to Express Possession

When you want to express possession, simply terminate the owning word with an apostrophe followed by an s as in these examples:

Fred’s book defines a book that belongs to Fred.
The cat’s toy belongs to the cat.

There are two exceptions to this general rule, as described in the following sections.

Using Apostrophes to Express Possession After Words Ending in s

When expressing possession for a word that ends in s, simply add an apostrophe and skip the addition of the following “s” as in these examples:

Bess’ book defines a book that belongs to Bess.
The kiss’ joy defines a kiss that possesses joy.

Next comes the final exception.

Using Apostrophes with It

When forming the contraction of the words “it is”, use an apostrophe as shown in the following example:

It’s snowing outside.
I think it’s too big.

When expressing the possessive form of the word “it”, simply add an s to the word as in this example:

There was smoke coming out of its nose.

Note that the standard case would be to add an apostrophe followed by an s but that this would confuse possession and contraction by making them the same.

I’ll see you in the classroom,