This is a big one. It is (it’s) so common it appears in virtually every writing help book. Why it’s so hard to remember is an unsolved mystery and bound to go down in its history, especially since it’s such an easy rule.

And editors go nuts over this one. It makes them want to send it and all its words into a black hole.

So, as you’re writing, just remember one simple rule.

 Separate the it from its “s”. If there is a has or an is in there, it needs an apostrophe.  If not, no apostrophe.

 It has something and it is something, but it cannot possess anything - ever.

Always. Every time. No exceptions to the rule. No passing go. No collecting $200. No way. No how. Never. Not even one time.