Find the right home for apostrophes.

That's the head for a language column by Paula Larocque in the Society of Professional Journalists' June-July Quill Magazine--a column that provides a nice overview of the proper and improper use of apostrophes.

She describes the apostrophe as "that elegant little squiggle" that "has only a few functions, yet it sometimes litters a patch of writing like shavings on a magnet.

"As punctuation goes, the apostrophe is simple:

"1) It marks the omitted letter or letters in a contraction. It's for it is. Can't for cannot. They're for they are....

"2) The apostrophe marks possession: John's desk. The desk's drawer. A whole year's work. Notice we could also say the desk of John, the drawer of the desk, the work of a whole year--'of' structures that show possession.

She points out that "with a single owner, add an apostrophe and then 's': John Smith's desk, John Williams's pen. (She also points out that the Associated Press Guidebook, and almost all newspapers, depart from that treatment, "omitting the 's' after proper nouns ending in 's': John Williams' pen.")

"With multiple owners, first make the proper noun plural by adding 's' (or 'es' to names that already end in 's') and then an apostrophe: the Bennetts' house, the Smiths' house, the Williamses' house, the Joneses' house. Plural generic nouns ending in 's' need only an apostrophe: the vampires' fear of garlic; the ducks' quacking chorus.

"Show joint ownership by apostrophizing the final noun: John and Mary's car. Separate possession needs separate apostrophes: John's and Mary's cars....

"3) The apostrophe marks the plural of letters, numerals, or symbols: He was holding three 6's and a pair of 4's. She earned two A's and three B's. Mind your P's and Q's.

"Current stylebooks usually omit apostrophes when there is more than one letter or numeral: They freed three POWs. He knows his ABCs. The airline bought a dozen new 727s. The roaring '20s (note that an apostrophe marks the omitted '19' but not the plural 's')."

Laroque also reminds us that possessive pronouns have no apostrophes: yours, ours, hers, his, theirs, its--a simple-enough rule that should keep careful writers from incorrectly using the all-too-common it's for the possessive, as in You can't tell a book by it's cover.