This week we're joined by a special guest blogger. Patricia T. O'Conner, a former editor at The New York Times Book Review, is the author of the national best-seller Woe Is I: The Grammarphobe's Guide to Better English in Plain English, as well as other books about language. She is a regular monthly guest on public radio station WNYC in New York. Learn more at her website, grammarphobia.com. Make her feel welcome!

For sheer readability, few things make as much difference as proper punctuation. These examples from You Send Me, a book I wrote with my husband, show how much difference punctuation can make:

"Who got fired, Stacey?" said the director.

Who got fired? Stacey, said the director.

Who got fired? Stacey said the director.

See what I mean? Now I can't tell you in a few paragraphs all you need to know about punctuation. But I can hit the high spots, the problems that come up most often.

1. The Indispensable Comma

The word "comma" comes from a Greek word meaning "to cut off," and that's what commas do. They cut sentences into pieces, organizing words into meaningful groups. Sometimes, the organization can make a big difference! Check out these sentences: (1) Jack said Harry wrecked the car. (2) Jack, said Harry, wrecked the car.

Here's some comma-sense advice:

"¢ Use commas and a connecting word (like and or but ) to separate clauses—groups of words with both a subject and a verb. John had forgotten her birthday five times in a row, but Gloria thought this year would be different.

"¢ Use commas between items in a list: Gloria was hoping for dinner, dancing, and flowers. She was furious that John hadn't made a dinner reservation, called the florist, or even bought a card.

"¢ Use commas before or after a quotation: Gloria said, "I might have known." "I'll make it up to you," John promised. But don't use a comma after a quotation that's a question or exclamation: "Why not kiss and make up?" John asked.

"¢ Use commas before or after the name of someone you're addressing: "Gloria, you're over-reacting," he said. "Maybe you're right, John," she answered.

"¢ Use a comma after an introductory remark if you want to emphasize the pause: Fortunately, the argument was soon over. Before long, they were cuddling on the couch.

"¢ Use commas around an aside, as you might use dashes or parentheses: He dialed Chez Panisse, their favorite restaurant, and managed to wangle a reservation.

"¢ Use commas around a clause that interrupts a sentence to insert a thought. These interruptions often begin with which , where , who , or when : They arrived at Chez Panisse, which was half an hour away, at ten. The waiter, who knew John and Gloria, joined them in a toast. (But don't use a comma if there's no interruption: John knew which wine was which. Gloria knew when she was ahead.)

2. The Underused Semicolon

The semicolon may be the most unappreciated and underused punctuation mark. If you find semicolons intimidating, relax. They're great for tidying up a series of items with commas inside them. Imagine how hard it would be to read this sentence if only commas were used: Jack willed his house to Jill, his best friend; his collection of lederhosen to his neighbors, Hans and Franz; and his dog, Tige, to a friend, Buster.

Semicolons are also handy for joining chunks of a sentence that could stand alone. A comma by itself isn't enough to hold together clauses like these: Jack broke his crown, Jill wasn't seriously injured. (This is sometimes called a run-on sentence.) Unless you want to add a connecting word, use a semicolon: Jack broke his crown; Jill wasn't seriously injured.

3. Chatty Quotation Marks

The trick with quotation marks is at the end of the quote. Does punctuation that follows the quoted material (period, comma, question mark, or whatever) go inside or outside the closing quotation marks? Here are the ins and the outs.

"¢ Periods go inside. "I think I'm getting the flu."

"¢ Commas go inside. "I probably caught it at work," he added.

"¢ Colons go outside. Elizabeth didn't like being called "Liz": it was so predictable.

"¢ Semicolons go outside. Don't play "My Funny Valentine"; she hates it.

"¢ Question marks and exclamation points are sometimes inside and sometimes outside. In most cases, they go inside the quotation marks: "What's your name, sweetie?" said the cashier. "It's not sweetie!" shouted the child. But question marks and exclamation points must go outside if they're not part of the actual quotation. Have you seen the film version of Gray's "Elegy"? Good heavens, I didn't even know they'd filmed Gray's "Elegy"!

"¢ Parentheses go outside quotation marks if the entire quote is parenthetical: Mom had the deciding vote ("I said no"). Parentheses go inside the quotation marks if only part of the quote is parenthetical. She added, "Next time, ask me first (if there is a next time)."

4. The Much-Abused Apostrophe

As someone with an apostrophe in her name, I hate to see this punctuation mark mistreated. Here's how it ought to be used.

"¢ Possessives. Apostrophes help show who owns what. To make a noun possessive, add either an apostrophe with the letter s ( 's ) or just the apostrophe alone, depending on the circumstances. The rules come in threes:

1. Add 's to a singular word or name, regardless of its ending. (Yes, even if it ends in s or x or z—whether sounded or silent.) Ms. Jones's favorite pastime is reading Camus's essays and collecting Degas's etchings. Her dog's name is Rex, and Rex's meals come from Paris's finest restaurants. Her dress's fabric is bamboo and her husband's shirts are Egyptian cotton. "It was Jacques's idea to live in France," she said, "after we declared bankruptcy in the States." 2. Add 's to a plural word that doesn't end in s. The children's shoes cost almost as much as the men's and the women's . My feet's bunions are killing me. 3. Add just the apostrophe to a plural word or name that ends in s. The Joneses' and the Smiths' and the Gonzalezes' houses were vandalized, and their cars' tires were slashed as well. The houses' windows were broken too. NOTE: When you need a comma or a period after a possessive word that ends with an apostrophe, the comma or period goes after the apostrophe and not in front of it: The idea was the girls', or maybe the boys', but at any rate the responsibility was their parents'.

"¢ Contractions. An apostrophe shows where letters have been dropped in a shortened word or phrase. For example, shouldn't is short for "should not"; the apostrophe replaces the o in "not." And I'll is short for "I will"; the apostrophe is a polite nod to the dropped letters. You can't say I didn't warn you.

"¢ Some unusual plurals. No, you DON'T add 's to a word or a name to make it plural! You can, however, add 's to form the plural of an individual letter. This makes for easier reading, and many stylebooks recommend it. At Swarthmore, Libbi got B's and C's and started spelling her name with two i's .

5. The Helpful Hyphen

Look what a difference a hyphen can make: The stolen sofa was recovered . Or, The stolen sofa was re-covered . Don't underestimate this handy punctuation mark. If in doubt about using a hyphen with a prefix, look it up.

When two words are combined to describe a noun, we sometimes use a hyphen between them. Generally if the compound follows the noun, it doesn't get a hyphen: That duck is water resistant. But if the compound comes before the noun, it usually gets a hyphen: That's a water-resistant duck. (And don't ask why a duck.)

Yesterday: Five Lessons in Grammar. Tuesday: Debunking Etymological Myths. Monday: Debunking Grammar Myths. Coming tomorrow: Pat will be answering your grammar questions. You can ask said questions in the comments.