I try really hard to be tolerant of the grammar and punctuation mistakes of others. I really do. After all, most of those rules are fairly arbitrary and ridiculous. In fact, a vast majority of the more technical ones were made up by some guy or other in the 18th or 19th century who wanted to make English more like Latin (which is both impractical and lame). But there's a fine line between rules that are completely ridiculous and those that make a person lose credibility when used incorrectly. For example: if you say "Those oranges is excellent," people are going to ignore the nice vocablulary and wonder if you ever passed third grade. One of these blunders, one that just so happens to be on my pet peeve list, is the confusion between "its" and "it's." For example:
(Good message; bad punctuation.)
Now, I'm sure there are a lot of people out there who are going to say that there's not really that big of a difference. Maybe there isn't. Maybe it really doesn't matter. Still, messing up your apostrophes will make you look like an imbicile every time, not to mention the fact that Henry Higgins is out there somewhere howling in pain. So, in order to help those who are less punctuationally aware, I will now spell it out for you in an easy-to-remember way that just might change your life forever. Or something.
First of all, you have to understand that like every other symbol in the written language, the apostrophe means something, and the meaning is actually very simple. When you see an apostrophe, you are indicating that something has been left out. Ta da! So when you're leaving something out (like the "a" in the contraction that I just used, which would be more formally spelled "you are"), put that apostrophe in there. When there's nothing to be left out, the apostrophe does not belong. That's right; it's not to be used to pluralize things. You can just save yourself a keystroke on that one:
Okay, so there's one, and only one, exception to this rule: the possesive. You're probably thinking that there's nothing left out when I say "Cecily's hair is shiny and soft." Well, you're wrong, but that's only because you aren't well-versed in Old English.* Since you probably don't speak Old English as a primary language, we'll just skip over that and say that we do it for reasons that most people have forgotten, kind of like wearing ties.** So, it's probably easier if you just think that you do it because you're supposed to, and get on with your life. Fourth graders do it every day.
This leads me to the it's and its conundrum: which is which? When do you use what to mean who? I don't know why this isn't more clearly taught in elementary schools, though I'm sure the teachers of America are doing their best. Here's the deal: "it's" means "it is" and "its" means the possessive form of "it." "Baby, it's cold outside," is just another way to say, "Baby, it is cold outside." Something is being left out, hence the apostrophe. Now, in a sentence like, "The apothecary saw his flask, filled with its deathly poison," you're not really leaving anything out, at least, nothing that most of us are actually aware of. So the basis of it is this:
"It's" equals "it is" equals something being left out equals apostrophe.
"Its" equals the posessive "it" equals nothing left out equals no apostrophe.
Really, the only reason that there is a difference is that when you use "it's" in both places, there are problems with clarity. So to make things clear, the punctuation wizards of days past decided that "it's" should have the apostrophe since the "it is" contraction actually gets rid of a letter in Present-day English. And there you have it. Learn how to correctly use apostrophes, Gentle Reader, and you will find that you will impress people of all social and grammatical circles.
Regards, best wishes, and careful proofreading,
-Cecily Jane*The apostrophe actually shows the loss of two letters in the possessive: "h" and "i." That's right; people used to say things like "George his sheep are in the pasture" instead of "Jojo's iPod is off the hook." I'm not sure how this was used in regard to both genders (like if they would have said "Jane her" or what); I'll have to do more research on the topic.
**It's bothered me for years, but I have no idea why guys are supposed to wear ties. I have decided that it's to hide the buttons on the dress shirt, but I have no empirical evidence.