Pity the poor apostrophe, friends and neighbors! This humble piece of punctuation has two jobs—just two—and it does these jobs without complaint, day in and day out. Does this stop people from abusing apostrophes at every opportunity? No, it does not. Apostrophes might be the most misused punctuation mark in the English language.
Contrary to popular belief, the appearance of an apostrophe does not mean that a plural is fast approaching. It would be easy to draw this conclusion from the number of times an apostrophe appears in this position. This mystery “’s” is called “the grocer’s apostrophe” because it often appears on produce signs advertising “tomato’s” and “potato’s,” and even “vegetable’s” for sale.
So, here are the rules when it comes to apostrophes. Apostrophes are used to show possession and to show where letters are omitted. That’s it. Nowhere else.
Okay, they’re a little more complicated than this, but not much more. Let’s look at a few examples:
When something is owned by one person or thing, use ‘s. “That is the dog’s dish.” This shows that the dish belongs to the dog.
When something is owned by more than one person or thing, use s’. “That is the dogs’ dish.” This shows that the dish belongs to more than one dog.
When something is just a plural, don’t use an apostrophe at all. Ever. “I see two dogs.” There’s nothing owned by the dogs here, so an apostrophe isn’t needed. See? Simple!
It gets a little trickier in a couple of instances. If a ball belongs to a group of children, is it the children’s ball or the childrens’ ball? Good question. The general rule is to use “’s” in this situation no matter what your gut tells you. The word is plural, but does not end with that s, so "'s" is accepted.
What about cases in which the word ends with an s? If we’re talking about the car that belongs to Mr. Jones or your boss, is it Mr. Jones’s car or Mr. Jones’ car? Worse, is it your boss’ car or your boss’s car? Despite what you might want to believe, it’s Mr. Jones’s car and your boss’s car. One owner, so it gets “’s.” The house lived in by the Jones family, however, is the Joneses' house. Since it's a plural and has a plural ending that ends with an s, it takes an apostrophe on the end. This prevents you from having to say something as painful as "The Joneses's house."
The exception here is with pronouns like his, hers, ours, yours, theirs, and its. You don’t write “hi’s car,” so you don’t write “it’s dish” either. We’ll talk more about “its” in a moment.
So, apostrophes indicate possession. They do not indicate that the letter s is fast approaching.
The other thing apostrophes do is show where letters have been omitted. You take a phrase like “do not,” crush everything together, and put an apostrophe in where the missing letters go to make “don’t.” So, if you understand this, you’re (for “you are,” the words get crushed together and the apostrophe replaces the missing "a") “gettin’” it. The apostrophe replaces the missing “g.”
So what about “it’s?” This word means “it is” or “it has.” Any time you see “it’s,” substitute one of those phrases. If it still makes sense, it’s (it is) right. That’s (that is) its (not “it is”) job.
Are there exceptions to this? Of course. The two that come to mind are "shan't" for "shall not" and "won't" for "will not." If you don't ask me to explain these, I won't complain.