The apostrophe is out to get you. That innocent-looking little punctuation mark you learned about in elementary school has been plotting against you all your life.
It's not like the hyphen, which is hard to master but equally hard to screw up. It's not like the semicolon, which you can eschew altogether with no harm done to your writing. It's not like the period, which quietly goes about its business ending sentences while confusing almost no one ever.
No, unlike every other punctuation mark happy to help your sentences run smoothly, the apostrophe goes out of its way to sow mayhem, tricking you into making mistakes you'll then blame on yourself.
Sound paranoid? It's the only possible explanation for why the plural possessive "children's" takes its apostrophe before the S while the plural possessive "kids'" takes its apostrophe after the S.
And it's the only way to understand why "Kim's" can mean either something belonging to Kim or the whole clause "Kim is." Pure evil.
Here are five ways the apostrophe tries to trip you up.
Who says, "Let us do laundry today"? No one. We say "let's." The uncontracted form is so rare that we're more likely to associate "let's" with "lets," which is the verb "let" conjugated in the third-person singular.
"He lets his hair down." "She lets the dog out." That makes it easy to accidentally use "let's" when we mean "lets."
"If you want to know whose coming, just ask." Did I mention the apostrophe has a co-conspirator? It's in cahoots with your computer's grammar-checker, which, if it's like mine, won't flag "whose" in place of "who's" in a sentence like the first one in this paragraph.
"Who's" with an apostrophe is a contraction of "who is" or "who has." "Who's there?" "Who's been eating all the cookies?"
The other one, "whose," is the possessive form: "Whose car is parked outside?"
Now flash back to your elementary school lesson on apostrophes. They're supposed to show possession, right? "Bob's car is parked outside."
But "whose" and "who's" turn that lesson on its head because the one without the apostrophe is the one that shows possession.
That brings us the pièce de résistance of apostrophe evil: its and it's. These, too, turn the apostrophe-for-possession rule inside out.
The one without the apostrophe is possessive: "The dog wagged its tail." The one with an apostrophe is a contraction of "it is" or "it has." "It's a beautiful day." "It's been great catching up with you."
But "its" and "it's" come up even more often than "whose" and "who's" — so often, in fact, that "it's" used as a possessive is one of the most common mistakes in the language.
Then there's "your" and "you're." You can know the rules backward and forward and still get these two mixed up. It's just so easy to type "your," the possessive form, in place of "you're," meaning "you are": "Make sure your on time tomorrow." That's an error. It should be "you're."
"They're" and "their" get confused the same way, though, interestingly, "there" doesn't seem to cause as many errors.
My favorite example of the apostrophe's cruel intentions is seen in department store directories: First floor: men's, women's, kid's. Oops. The rules say that when a noun is plural you make it possessive by putting an apostrophe on the end, as in the cats' tails.
But there's an exception. Some plurals don't end in S. They include men, women and children. For these, the rule is to add an apostrophe then an S: men's, women's, children's. But the plural of "kid" does end in S: kids. So the plural possessive is kids', breaking ranks with men's and women's.
Sometimes it seems that no one can keep this one straight. You'll see a "kid's menu," leaving you wondering who the lucky kid is. Or you'll see a childrens menu, leaving you wondering what happened to the apostrophe. It's all part of the apostrophe's evil plan.