Guest post by Linda Aragoni
For their size, apostrophes cause writers an extraordinary amount of grief. Fortunately, understanding the two primary functions of apostrophes will prevent most of that grief.
The first main use of the apostrophe is to create possessive nouns. When we say an apostrophe creates a possessive noun, we mean the apostrophe shows that whatever follows the word containing the apostrophe is possessed by, or belongs to, the person, place, or thing named by the word containing the apostrophe. Both the possessor and the thing possessed are nouns. The cat's paw is the paw that belongs to the cat. The boys' coats are the coats belonging to the boys.
The second main use of apostrophes is to replace letters in contractions. Take, for example, the sentence, "I have not had lunch yet." In informal writing, you might write "I haven't had lunch yet," squeezing out the space between have and not and replacing the O with an apostrophe. Letters squeezed out of contractions are usually vowels.
If you know just this much, you can test whether a particular apostrophe is used correctly.
Look at this sentence: the limit is three DVD's per family. Ignore everything before the word containing the apostrophe. Then put the words belonging to after the word containing the apostrophe. "The limit is three DVDs belonging to per family" makes no sense, so the apostrophe cannot be correctly used to indicate a possessive noun.
Now see whether the apostrophe is correctly used to replace letters. Neither "three DVD is per family" nor "three DVD as per family" makes sense.
Those two tests tell us the apostrophe in the example does not belong there. Correctly written, the sentence reads, "The limit is three DVDs per family."
Try the same two tests with this sentence: the dog returned to it's owner. The word containing the apostrophe is not a noun but a pronoun. That means the apostrophe cannot be used here to create a possessive noun.
Now check whether the apostrophe is being correctly used to create a contraction. Neither "the dog returned to it is owner," nor "the dog returned to it as owner" makes sense.
You can safely (and correctly) conclude that "the dog returned to its owner" does not require any apostrophe.
In nearly every case, understanding these two uses of apostrophes will allow you to determine whether you have used the problematic little mark correctly in your writing.
While teaching first-year college students, writer-editor Linda Aragoni taught students study skills for learning enough grammar to correct their own papers. Her e-book Grammar Abusers Anonymous teaches mature high school and adult students how to master grammar in their writing.
Copyright 2010, Linda G. Aragoni.