Welcome to the Grammar Minute, where we’re saving the English language sixty seconds at a time! I’m Lauren Smyth, and I’m back with another episode on pluralization and apostrophes. Let’s be real: It’s confusing. But it’s also one of the easiest grammar mistakes to notice, which makes it an absolute no-no for professional writing.

Here’s your quick guide to apostrophes and pluralization.

If you have a word like “coffee,” the correct way to make it plural—coffees—is simply to add an s. Easy!

If you have a word like “cat,” and you want to talk about “the cat’s bed,” then you add apostrophe-s.

Apostrophe-s can also be short for “is.” If you want to say that Rachel is going to her friend’s house, you can write “Rachel-apostrophe-s.”

So, to recap: Apostrophe-s means either possession or “is.” It doesn’t ever mean pluralization. Ever. Under no circumstances whatsoever. This is one of the rare occasions where English, conveniently, has a hard-and-fast rule.

That’s your Grammar Minute! Visit thegrammarminute.com for more tips and tricks.