Imagine the power of the comma.

It's possibly the most important punctuation mark in the English language. In one fell swoop, a comma can connect ideas, organize thoughts and remove ambiguities. In some cases, it can even save lives.

Save lives?

You bet! Take a look at these examples of how a misplaced or missing comma can dramatically alter the meaning of a sentence:

"Let's eat grandma." vs "Let's eat, grandma."

"Stop clubbing, baby seals." vs "Stop clubbing baby seals."

"We're going to learn to cut and paste kids." vs "We're going to learn to cut and paste, kids."

"I love cooking my family and my dog." vs "I love cooking, my family and my dog."

Grammarian Lynne Truss, author of the spirited and scholarly "Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation," makes a powerful case for proper punctuation in her New York Times best seller.

"The reason to stand up for punctuation is that without it there is no reliable way of communicating meaning," she says.

Are you punctuating properly?

To help you avoid misusing some of these powerful little marks that keep our our language alive, we've assembled a list of 10 common punctuation errors. These errors can undermine your credibility, confuse your audience and wreak havoc on a perfectly thought-out paper. And if you're a student in one of Saint Leo's online degree programs, you might find it to be a helpful checklist for your next paper or essay.

1. Putting apostrophes where they don't belong.

An apostrophe is used to form contractions (it's, can't, don't) and to indicate possession (Tom's, Mary's, my family's). Generally speaking, for singular nouns that end in "s" (boss), the possessive is formed by adding -'s (boss's car). For plural nouns or names that end in "s" (boys, James) the possessive is formed by adding an apostrophe after the "s" (boys' clubhouse, James' book). An apostrophe is never used to form a plural.

2. Putting punctuation on the wrong side of quotation marks.

In American English, punctuation goes inside the quotation marks, even if the punctuation is not part of the quotation itself. For example: Mary said, "It's time to eat."

3. Using a semicolon where a colon belongs.

A colon is used to set off a list (I ate three things: chicken, broccoli and a potato.). A semicolon is used to separate two related but distinct thoughts (I was so hungry; I hadn't eaten since breakfast.). When using a semicolon, check to make sure that both thoughts contain a subject and a verb, and are able to stand alone as a complete thought.

4. Fusing two sentences with nothing more than a single comma.

Using a comma alone to connect two complete and separate thoughts causes a "comma splice" – that punctuation faux pas your eighth-grade teacher warned you about. For example: My dog loves to play, I gave him a ball. There are three simple ways to fix a comma splice: change the comma to a semicolon, make each clause a separate sentence, or add a coordinating conjunction (for, and, nor, but, or, yet, so) after the comma.

5. Using multiple punctuation marks for emphasis.

No matter how happy, angry, excited or in love you may be, stick to one punctuation mark at the end of a sentence. No exceptions! Multiple exclamation points, question marks or ellipses (three dots) may be perceived as condescending and tend to suggest an over-emotional writer.

6. Using a comma before the conjunction in a simple list.

For short and simple lists (bananas, apples and oranges), the last comma – the one right before the conjunction, usually "and" or "or" – is completely unnecessary, but not wrong. If you can't break the habit, at least be consistent. For longer or more complicated lists however, use a final comma before the conjunction. For example: A good athlete listens to his coach, practices every day, and always gives his best effort."

7. Putting two spaces after a period.

Nothing screams your age like two spaces after a period. The two-space rule dates back to the days of manual typewriters and monospaced fonts, when an extra space made text easier to read. Today, thanks to computers and modern, proportional fonts, adding two spaces after a period no longer enhances readability. In fact, typographers say the extra space actually diminishes readability.

8. Using quotation marks when there isn't a quote.

Generally speaking, quotation marks are reserved for direct quotations and certain titles. For a quote within a quote, single quote marks are used. For example: "I heard him say, 'I already ate,' before he left," Mary recalled. Quotation marks should not be used for emphasis ("free" candy, "hostile" workplace).  

9. Using a dash when a hyphen will do.

Use a hyphen, or short line, to join two or more words together so they act like an adjective before a noun (sour-smelling rags, bread-making machine, 3-year-old girl). Hyphens are also used for some compound terms (eye-opener, well-being, merry-go-round), but never when the word preceding the adjective ends in –ly (heavily fortified troops, newly inducted members). A dash, or longer line, indicates a separate, but related idea – an interruption that disrupts the flow of a sentence. For example: My favorite pastime – I hate to admit – is reading old comic books. Generally speaking, dashes come in pairs (with space on either side of the dash); however, they can stand alone when they come at the end of a sentence. For example: I started a new diet today – once again.

10. Using too few or too many commas.

Oh, those commas; they're so misunderstood. Let's talk about the basics.

First, always use a comma after an introductory element – which can be a sentence or an individual word. For example: Before going to the gym, I drank two glasses of water. Another example: Meanwhile, the meter kept running.

Second, always use commas around interrupters – additional information that appears in the sentence but is separate from the primary subject of the sentence. For example: Bill Robbins, a freshman from New Jersey, was the team's first choice for quarterback. To decide if you need commas around an interrupter, try taking the interrupter out of the sentence completely. If the sentence is still clear, then you probably need commas. Commas should also be used between describers – adjectives not separated by a conjunction used to modify the same word (dirty, smelly dog).

Last, use a comma before a conjunction (such as for, and, but or so) to join two independent thoughts. For example: I didn't study all weekend, so I will have to work extra hard this week. One more example: She likes to cook, and she's also a great volleyball player.

Are you an offender?

It's hard not to commit a punctuation offense every now and then. In fact, sometimes it's even hard to tell. The rules aren't always clear, exceptions abound, and experts don't always agree. But if you study this list, chances are you'll come close to punctuation perfection – and that will impress your professors, bosses and clients down the road.

But enough about the rules; it's time to get this National Punctuation Day party started!

And what better way to start the celebration than a few of our favorite quotes about punctuation:

  • "Cut out all of these exclamation points. An exclamation point is like laughing at your own joke."
    – F. Scott Fitzgerald

  • "No iron can pierce the heart with such force as a period put just at the right place."
    – Isaac Babel

  • "If the semicolon is one of the neglected children in the family of punctuation marks these days, told to stay in its room and entertain itself, because mummy and daddy are busy, the apostrophe is the abused victim."
    – John Humphrys

  • "Used sparingly, the semicolon emphasizes your crucial contrasts; used recklessly, it merely clutters your page."
    – Sheridan Baker

That's all for now. It's time to go back and read the last thing you wrote.

What's your punctuation Achilles heel? Commas? Apostrophes?

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