I recently volunteered to write a (non-credited) pilot test of a certification exam for the Editors Association of Canada. It was their copy editing exam, and it was three hours long. I didn’t believe it would really take me that long until I wrote the practice test they provided … and looked up 2.5 hours later, starving and stiff in the neck. As it turned out, the pilot exam took me about the same amount of time, leaving me 30 minutes to check my work and obsess over things left undone and unknown.

It was a hard thing, and even if I pass, I won’t get credit for it, but I’m glad I did it, mostly because I learned that I’d been making some very simple English mistakes over and over for my entire life. That’s hard to swallow as a professional writer and editor, but it was good for me. I feel better knowing, and am able to move forward and do better, more accurate work now. Learning is awesome, but it’s also painful at times.

The biggest and most egregious error I was making involves (unsurprisingly) the evil comma, that most confusing of punctuation marks. As you may know, some commas are optional, and used to impart a particular style or rhythm to a sentence or passage. Some are required at all times when a particular situation arises. Tell me which of the following two sentences is incorrect:

Jane lives in St. John’s, Newfoundland, and has seven cats.

Joe lives in Halifax, Nova Scotia and has four dogs.

Say them aloud. They sound about the same, right? Different people, places, and animals, but essentially the same sentence. The issue is that second comma, the one after “Newfoundland” in the first sentence. It’s required, not optional. And no, I’m not joking. I was shocked. I’ve been writing as though the second version was correct all these years, and I am completely wrong, according to both the Chicago Manual of Style (16^th edition) and Editing Canadian English (3^rd edition). The latter states in section 7.3.5 that commas “set off the second element in geographical entities … whether abbreviated or not.” It also notes that “omission of the second comma is a frequent error,” so I feel a little better knowing I’m not the only one who had no bloody idea.

Ready for another kick? The same is true of years in text where the date style used is month/day/year: the year must be enclosed in commas. Like so:

On September 15, 2016, I was in Cornwall, England.

That final comma is non-negotiable. (Also, I wish I was in Cornwall right now.)

So if you feel like waking up your brain, I highly recommend reading a grammar or style guide once in a while, because although you might think you know everything, it’s highly probable that you’ll actually discover something you’ve been doing wrong all along. And if not, you’ll get to feel incredibly smug about it, which is also awesome. (Please, if you knew about this comma thing, go ahead and lord it over me. I can take it.)

What crazy grammar, style, or punctuation rule makes you shake your head in amazement?