"Have your photo's enlarged for just $1.99!"

Those were the flashing red words on a huge drug-store marquee when I drove by last week. And as I type this in Word, it doesn't understand the problem.

The problem is: That sentence -- the word "photos" -- does not need an apostrophe.

Apostrophes serve several purposes, the two most common are to show possession and contraction. (As a refresher, a contraction is a shortened form of a word or group of words where the missing letters are replaced by an apostrophe. Example: we+will=we'll, should+not=shouldn't.)

The word "photos" as it should be above is simply plural, not possessive. And it's certainly not a contraction.

Example: We'll take John's car to the meeting.
Example: Don't let Julia's daughter leave before giving her a hug.

Other not-so-common uses of the apostrophe
An apostrophe is used when one or more letters or numbers have been left out of a word.

Example: I am part of the graduating class of '90.
Example: Top o' the mornin' to you!

Another rule, one that looks funny and is hard to remember because it does: When a word calls for two apostrophes, simply eliminate the second one.

Example: Patrick is learning the do's and don'ts of driving in Nashville traffic.

Which brings up the final common use of apostrophes: Use an apostrophe when creating the plural form of a letter, number, sign or word discussed as a word, not as its form of speech.

Example: He knows the do's, now he just needs to work on the don'ts.
Example: Please remove all B's and 9's from this page.

If you're just bustin' at the seams to learn more, Grammar Girl takes the apostrophe discussion a step further in a recent post. Enjoy! We sure do.