The apostrophe is one of the most misunderstood punctuation marks in English, mainly because it serves two distinctly different functions.

The first function is the easy one, and the one most likely to be used correctly. An apostrophe is used to show that two or more words have been combined by dropping letters and putting the apostrophe where the letters are omitted. You may know them as contractions. Here are some examples: don’t = do not; could’ve = could have; I’ll = I will; he’s = he is. Pretty simple, right?

The apostrophe is also used to show ownership or possession. That’s the hard one to keep straight because it involves the -s ending on nouns, and an -s on the end of a noun can mean possession or it can simply mean plural (more than one of something). So when you have an -s on the end of a noun (name of person, place, thing, idea), you need to decide if the noun is simply plural or if it owns or possesses something. If the noun is simply a plural word, then no apostrophe is needed. If the noun possesses something, then you do need an apostrophe.

Here are some examples of simple plurals:

  • Many apples fell from the tree during the storm.
  • The publisher rejected his manuscript because there were too many errors.
  • I looked at five different cell phone plans before choosing one.

Here are examples of noun possessives:

  • The dictator’s speech frightened my parents.
  • Jack’s inability to concentrate is having an effect on his job performance.
  • The doctor was unaware of that patient’s history of seizures.

The only other complication is seldom seen or used, but you need to be aware of it, and that is the use of the apostrophe in nouns that are already plural. You may remember this use from pages of drill foisted on you in school by a well-meaning but overly zealous teacher. The rule is actually simple. Whatever is before the apostrophe is the root word. If the root word is singular, then the apostrophe goes before the -s. If the root word is plural, then the apostrophe goes after the -s.

Here are some examples:

  • my brother’s room (one brother occupies the room)
  • my brothers’ room (more than one brother occupies the same room)
  • the parent’s wishes (one parent has wishes)
  • the parents’ wishes (more than one parent has wishes)

Don’t be afraid of that little “upstairs comma.” Use it correctly and you’ll be the envy of all your friends!