How to Use a Comma

Punctuation is all about communicating well. Of course, most people have little trouble with end punctuation. Whether our voice goes up or down at the end of a sentence lets us know whether a question mark or a period is appropriate. An exclamation point follows a sentence that expresses a certain energy. 

Commas, however, are a different story. Many people get nervous about how to use a comma, so the current trend is to leave commas out altogether. But when a writer leaves out commas, as is done in a lot of online writing, the pacing of a sentence is changed. Sometimes the meaning is changed, too, from what the writer intended to say. This can cause confusion. It can also make an article difficult to read, and frustrated readers are quick to leave your webpage.

This in itself is reason enough to refresh your memory on when to insert a comma and when to leave it out. 

• Basically, a comma tells the reader to pause. 
• When you connect two independent clauses with "and," "or," or "but," add a comma before the connecting word: It's raining cats and dogs today, and I left my umbrella at home.  "It's raining cats and dogs today" can stand alone as a sentence by putting a period at the end. The same is true of "I left my umbrella at home." To connect the two complete thoughts, you need to add a comma and the conjunction, or connecting word, and.
• A comma follows most beginning subordinate clauses just before the main, or independent, clause begins: When I go for a walk in the dark, I bring along my flashlight. 
• When a long prepositional phrase begins a sentence, it is followed by a comma: During the long, cold nights of a Canadian winter, we huddle by the fire and read a good book. 
• This last example also demonstrates the way we separate some adjectives that appear together. The rule is if you can insert the word and between the two adjectives, you can use the comma. 
• A comma precedes and follows a person's name when you are addressing him or her: Barry, would you like a cup of tea?
• Commas appear on both sides of a word or a phrase that can be taken out of the sentence without changing the meaning of the sentence. For example, if I tell you that “my friend Beth followed me into the room,” I only use commas before and after “Beth” if Beth is my only friend. If I have more than one friend, I leave out the commas because the name “Beth” is important information in the sentence; it tells which friend I am talking about. If Beth is my only friend, however, then the name is implied in the word “friend,” and so commas are added before and after her name. If I were to delete her name, the meaning would still be clear. 
• Words such as "however," "of course," "therefore," etc., are also preceded and followed by commas for the same reason. They are referred to as "parenthetical" or "an interrupting element." If you were to take them right out of the sentence, they wouldn't change the meaning.
• Another way this concept may come up is if you use a nonrestrictive phrase or clause to describe something or someone: The girls, who had always loved to jump rope, spent the afternoon memorizing jump rope songs. Put commas before and after the describing phrase or clause. On the other hand, if the clause or phrase is necessary to distinguish these girls from some other girls, you leave the commas out: The girls who loved to jump rope invited the girls who had never tried it to join them. No commas are added because the information is needed for the sentence to make sense.
• Use a comma to separate words in a series: I like the colors blue, green, and purple. Some people prefer to leave out the comma before the “and.” I tend to add it, as it prevents confusion. (Is it the combination of green and purple that I like or each color on its own?)
• You need a comma between a city and a state or province when you use them in a sentence: I used to live in Pomfret, Vermont.
• Add a comma between the date and the year: Today is April 26, 2012.
• Use a comma to set off a title or degree: The lecture was delivered by Laura Montague, Ph.D., at Collins Hall.

The meaning of a sentence can become fuzzy when commas are either added when they are unnecessary or left out when they are called for, as was demonstrated by the author of the following book. She added an extra comma in the title of her grammar book to demonstrate the kinds of confusion that can result when such a small curlicue is misused. Look carefully at the illustration on the cover if you have any confusion about why that title is funny.

I like this version of Lynne Truss's book even better. The illustrations add to the hilarity of her approach. She is unapologetically British in her references and in the rules she explains. The U.S. grammar rules are slightly different in some cases.

Eats, Shoots & Leaves Illustrated Edition

Unfortunately, even after learning what the "rules" are for commas, some people find using them tricky. There are cases where you should not use a comma that on first look resemble places where commas are recommended.

There are other places where commas are optional, depending on the style of the writer.

I've an upcoming article on these cases to show what I mean.

And, as I said at the beginning of this article, many people who write online have dispensed with comma use altogether, possibly because they are writing quickly and can't be bothered to go over their work with the eye of an editor.

Because punctuation is a convention that has been agreed upon and carefully taught as a way to ensure our communication is clear, however, I think we should at least try to be more careful how we use it.

I'm sure you'll agree with me when I say that miscommunication has often been the culprit for family feuds and even wars. On a more mundane level, I know I have at times purchased something that I thought was supposed to be one thing and found out later that I'd misunderstood what I'd read on the label.

Kids can be funny at how they misinterpret what they think they hear the adults say.

Older people (like Mr. Magoo) can get funny ideas when they mishear conversations, too.

These examples can be funny, but they can also sometimes be tragic.  As writers, we are responsible for the words we use and how we get our messages across. Punctuation is one way we can be sure that what people read is indeed what we were trying to convey. That's why people started to use agreed upon punctuation in the first place.

Maybe the world is changing so fast that the language is changing with it, and we will one day no longer share these rules of punctuation. I hope, however, that the goal of clear communication is not swept away with the discarded rules.