Those of you who read a lot of students' papers (say, if you're a peer writing tutor or something) or who just spend a lot of time on Facebook will likely run into a piece of composition that resembles this:
I did so many thing's today! First I had egg's and waffle's for breakfast, and then I gathered my book's and thing's for school. I found out I had to read several chapter's because my teacher's will have lot's of test's for us over the next few day's. Then my friend's met me after I ran some errand's, and we went to two different party's! I only had three drink's, but I still had my parent's pick me up. I would hate to crash into all those car's on the road's!
It is staggering to see how misued—nay, abused—the apostrophe has become. More and more commonly, the apostrophe is egregiously deployed to make plural nouns when, in fact, making a noun plural typically involves nothing more than adding the letter "s" to the noun sans the apostrophe.
Turning a singular noun into a plural noun? No problem. Just add an "s."
Granted, pluralizing a noun becomes just a tad trickier when the noun is supposed to undergo a bigger change, but whether you like it or not, still no apostrophe is needed. The example above, for instance, has party's, whose correct plural form is "parties." Ugh.
Okay, now that I've addressed simple plural nouns and their incompatibility with apostrophes, let's take a look at what apostrophes are actually meant for.
The first use of an apostrophe is to mark a noun—whether singular or plural—as possessive. Here are some examples:
When the noun is singular, the apostrophe is followed by an "s," as in
The cat's bowl or
Bruce's car or
The school's headmaster.
When the noun is already plural, the apostrophe follows the "s," as in
The books' covers or
His dogs' leashes.
The second use of an apostrophe is to indicate omitted letters in contractions. Here are some examples:
Don't = Do not
Won't = Will not
Shouldn't = Should not
It's = It is
They're = They are
On a related note, occasionally apostrophes are used to omit letters in informal writings, such as when the writer is attempting to reflect the idiosyncrasies of slang or a regional dialect, as in
I'll be gettin' there soon! or
He's just killin' time and chillin'.
And that's it: the two main uses of the apostrophe in the English language. Unless you're using the apostrophe for one of these two purposes, please leave the poor thing alone.