It's and Its

It’s = it is

Its = something belongs to “it”

Why We Confuse Them

The use of the apostrophe for “it” differs from one of the two general uses for apostrophes that we are taught in primary school:

1) To show a contraction of two words.

When we contract two words, an apostrophe replaces the contracted letters.  “It” follows this rule:

have + not = haven’t

I + am = I’m

they + are = they’re

she + will = she’ll

let + us = let’s

it + is = it’s

2) To show possession.

When we want to show that somebody/something owns an object, or that an object originates in or is part of somebody/something, we affix an apostrophe s (’s) to the end of that somebody/something.  “It” does not follow this rule.

Tom’s friend = the friend of Tom

The dog’s collar = the collar of the dog

Shakespeare’s plays = the plays of Shakespeare

The city’s hospital = the hospital of the city

The Cat in the Hat’s hat = the hat of the Cat in the Hat

But

Its colour = the colour of it

Possession for “it” is an exception to the apostrophe s rule, quite possibly because “it’s” is a contraction for “it is.”  The possessive of “it” is “its.”

Resources

The following post-secondary institutions have good interactive worksheets to practice this difference:  The University of Bristol, Santa Monica College, and Capital Community College.