Saylor.org's English Composition/Apostrophes
The apostrophe (') is a punctuation mark with an unfortunate tendency to be misused. As it exists, there are three uses of the apostrophe in the modern English language.
- The marking of the omission of one or more letters (as in the contraction of do not to don't).
- The marking of [possessive case (as in the cat's whiskers).
- The marking as plural of written items that are not words established in English (as in P's and Q's, the late 1950's). (This is considered incorrect by some. The use of the apostrophe to form plurals of proper words, as in apple's, banana's, etc., is universally considered incorrect and is called a greengrocer's apostrophe.)
While this seems fairly straightforward, there are few errors of apostrophe use that are commonly made. In the case of singular possessive words that end with the letter 's', it is generally accepted to add an apostrophe but not an extra s (Jesus', Moses', Thomas'). In the case of plural possessive, there is often confusion, as well. Say you're talking about a dog owned by a family named the Thompsons. Do you write "the Thompsons dog", "the Thompson's dog", "the Thompsons' dog". The answer, like the case of singular possessive that end with 's' is "the Thompsons' dog". If you chose the first you would imply that it was a type of dog called Thompsons and the second would make it seem as if only one Thompson owned the dog, when then entire family of Thompsons did.
Going a step further, problems often arise when compounding plurals and possessives. Look at these distinct examples: My friend's cat's food (the food of my one friend's one cat) My friends' cat's food (the food of my multiple friends' one cat) My friend's cats' food (the food of my one friend's multiple cats) My friends' cats' food (the food of my multiple friends' multiple cats)
When apostrophes become confusing like this, one sympathizes with would-be reformers of the English language, such as George Bernard Shaw, who hope to rid the language of this particular punctuation mark. But just imagine seeing:
"My friends cats food"
and trying to figure out what that meant from context alone.