When teaching possessive, teachers usually say, “To make it possessive, add an apostrophe.” That’s true if you want to say Susie’s book or the dog’s bone. It’s also true if have a plural noun and need to say the dogs’ bones or the kids’ desks. Even I have repeated the mantra possessive has an apostrophe.
Rules in the English language are meant to be broken. Students have been known to ask, “If there are so many exceptions, how can they call it a rule?” Even so, one exception to the possessive rule should be memorable.
Its is the only possessive that has no apostrophe.
I want to look at its flower.
How can it wag its tail?
I think its hat is green.
The gods who designed the English language couldn’t put an apostrophe in the possessive its for the same reason Disney couldn’t give Hades his real Greek name in the movie Hercules. The correct Greek name was already in use–Pluto. How could Disney create a new bad guy and name him after the lovable dog? Likewise, its cannot have an apostrophe because the word already exists with the apostrophe.
It’s is a contraction. When you use the word it’s you always mean ‘it is.’ Always.
It’s going to be a hot day.
I want to know if it’s making a mess.
Can you tell me if it’s happening today?
So, very easy. Only use it’s if you mean to say it is. That’s it. No exceptions.