He doubts that any visitor to this site – should anyone ever visit, that is – needs a primer on its/it's. So let's enjoy a few moments of schadenfreude and move on. It's/its can't be a problem in the days of No Child Left Behind, right?
Wrong. And the Web makes it ever so easy to find bunches of its/it's gaffes.
Here's just some of the carnage on Google News:
its a: One has to weed out business articles mentioning companies' bond ratings (its A-rating) and then sort through a lot of disappointing comments – Note to Google: Please allow Mr. Rewrite to exclude comments from searches – but one will find plenty of errors in MSM articles and in blogs attached to credible brands.
its the: Same deal here – mostly comments, but one will find plenty of articles and bloggers who should know better.
It's a dark moment when Mr. Rewrite sees an its/it's error in copy. Sometimes it's a typo. But usually it comes up again and again along with other grammar/usage basics. It's a deep hole from which to escape.
With that in mind, Mr. Rewrite will offer a primer after all: its is possessive; it's is a contraction of it is. Enough said.
Mr. Rewrite occasionally sees its' in copy, with writers apparently thinking that possessives always require an apostrophe. Here's an example from Mr. Rewrite's workplace:
At the risk of entering the world of grammar, which exposes him to arrows from true grammarians, Mr. Rewrite will offer this: With only one exception, personal pronouns don't use apostrophes to form possessives. His and mine are easy, but writers sometimes get into trouble with hers (her's), ours (our's) and occasionally their (their's). Mr. Rewrite suspects much deeper problems than possessive/apostrophe confusion when he sees their's.
The exception among personal pronouns: one's. That's rarely used in American English, but Mr. Rewrite employs it to achieve his stuffy, snooty tone.
Here's a good summary of its/it's from Paul Brians' Common Errors in English Usage.
It's time to get back to work.