The grammar of "its" vs "it's"

I made an error - corrected hastily before anyone could notice - in the last post that Ramya (wife, proof reader, grammar nazi) noticed, and then proceeded to give me a grave and admonishing look.

So, here's the rule for when to use "it's" and when to use "its": Use "it's" when you can use "it is", eveywhere else use "its".

Now, venture forth and conquer the world, thou proud grammaticus constructivus!

More like this

Ten Words You Need to Stop Misspelling (detail) view the whole thing at The Oatmeal - it's great. While blogging late at night, I've sometimes wondered whether an extensive study of blog comments would yield a set of emergent categories, which could then be organized into a sort of phylogeny…
Orac post-publication note: There is reason to believe that one point I made below could well be incorrect. However, even leaving that point out, there are still many reasons to doubt the authenticity of the text exchange I discuss below. See the first 10 comments for a discussion. Unlike AoA and…
I had a newspaper route up until I was in the ninth grade, and what I dreaded about the job was going door-to-door collecting subscription fees. The worst part was probably the odors in some of the houses. One house emanated a toxic mixture of Lysol, alcohol, pet dander, and cigarette smoke. These…
At least this is the standard if you are Roger Pielke Jr and the accused is a member of Real Climate. When pressed as to how he knew an accusation of plagarism he was leveling was really true, in his own words: if the authors provide evidence [...] I'll stand corrected. [...] Meantime, I am…

Another way to look at it:

You wouldn't write hi's and you wouldn't write her's, so you also don't use it's for the possessive. Though, if you see enough other people making the mistake, eventually your brain turns off regarding seeing the problem.

As a side note, Thomas Jefferson almost always used it's as a possessive. (On the other hand, spelling rules back then really hadn't crystalized.)

There is an additional problem. We have two nearly identical keystroke sequences, and it is our weak right pinky finger that is responsible for the apostrophe, so even when the brain sends the squence "it's" we may see "its" show up; furthermore, "its" may misfire and come out as "it's".

For what it's worth, I forgive you.

Sorry to be so late commenting, but I just noticed your post. Your rule is useful as far as it goes, but needs an addition:

--Use "it's" when you can use either "it is" or "it has"; everywhere else use "its."

Thus,

--It is late. It's late.

--It has been raining. It's been raining.