Look, I try to be a nice curmudgeon, and I don’t normally get all outraged over people’s little mistakes. These things usually don’t really matter, in even the medium-size scheme of things, and besides, everyone is ignorant about something and everyone makes mistakes. But this, this chaps my hide.

I use postsecrets.com to teach my 11th graders spelling & syntax; we correct your secrets.

This was posted to Postsecret on Sunday, and there are a few things I could argue with here, but I’m really only interested in one. I am not going to knock this teacher for the incorrect URL, which is probably just the handwritten equivalent of a typo, nor for the semicolon after “syntax,” though I would use a colon or an em dash—it’s not strictly wrong, so I’ll chalk it up to writer’s choice. I will also ignore that the writer of the original postcard is being marked down for using all caps and not making a complete sentence out of “Sorry,” although those things are perfectly acceptable in context. I’m guessing the assignment is to mark up the cards as if they’d been turned in as part of a school assignment, and in that case the corrections are strict but not out-of-bounds.

No, what set me off is the mark after “baked good”—can you see it? The teacher crossed out the writer’s em dash and put in—gasp—a semicolon. The teacher is right about the dash; it is incorrect.* But a semicolon is most definitely not an acceptable replacement.

Let’s look at the original writer’s sentence: “If you come into the bakery with a sugary coffee drink and buy a sugary baked good—I judge you.” The teacher saw that everything after the dash could stand as a sentence on its own and thought, “Independent clause! Semicolon!” But remember, a semicolon joins two independent clauses, and the first half of that sentence is a conditional clause, not independent at all. Independent clauses are the easiest to spot because you just isolate them and see if they still make sense as a sentence. Watch: “If you come into the bakery with a sugary coffee drink and buy a sugary baked good.” Clearly that sentence isn’t over, so that clause is definitely not independent.

Normally I’d give this person a pass—as I said above, no one knows everything, and everyone makes mistakes. But in this case it does matter, very much, because this person is a teacher. This person has a room full of 16- and 17-year-olds who are trustingly absorbing their views on the semicolon, and who are going to confidently and incorrectly deploy that punctuation mark in college applications, résumés, and, worst of all, articles that I may have to edit one day. It’s worse than teaching them nothing about the topic. Someone who knows they know nothing is (usually) easy to teach and happy to learn. Someone who thinks they know something is impossible. Telling them they need to be re-taught something sounds, to them, like, “You’ve embarrassed yourself by doing this wrong for years and everything your beloved authority figure told you is a lie.” They get as defensive as if you’d insulted them, their hometown, their upbringing, their whole way of life. That’s why wacky and completely bogus “rules” like “never split an infinitive” hang on. There’s no basis for them, but acknowledging that they’re incorrect feels like betrayal.

Which is not to say that teachers have to know everything. Of course they don’t. But I do wish they’d ask when they’re unsure of something like this. So teachers, I don’t know you, and this is crazy, but here’s my website, so write me, maybe?

*All they needed was a comma.