Nusa Dua coast with breakwater, Bali, Indonesia

The most wonderful day of the year.

Er, comma—at least it seems like that's what we're seeing. And just like a comma breaks up a sentence, this structure called a breakwater interrupts the Pacific Ocean, punctuating waves with a crash before they can disturb this Bali beach. Whether its resemblance to a comma (or is that an apostrophe?) was intentional or not, it's a fine visual for today's syntactical celebration. That's correct: It's Grammar Day! (Note to hardline grammarians: We know punctuation—like a comma—isn't exactly grammar, but we're loosening the linguistical reins a bit in the generous spirit of Grammar Day. So put that red pen down, smarty-pants.)

If you're not inclined to decline nouns or dying to diagram a sentence, don't quit reading just yet. You might just think of grammar as the dos and don'ts taught in English textbooks—but a mere stuffy set of rules it ain't. Grammar is the ingredients of a language. Whenever we speak or even think, whether with prim-and-proper diction or in the most teacher-defying slang, our brains are using grammatical rules to translate firing neurons into words and phrases. Just how this happens is still a hot debate for linguists: Are these rules based on hardwired neural pathways or are they learned from a young age?

Well, however the brain works, we hope you brought yours today. Our quiz covers those wonderful, nitpicky grammar rules from school you doubtless remember so well. Sharpen your pencils!