The Grammar Police: the Correct Use of Commas

Commas are one of the most confusing and overused punctuation marks, but also one of the most useful and important. Using commas correctly creates a flow and rhythm to your writing that makes it easier for your reader to understand the message you are trying to convey. Creative writers may use literary license for the sake of style, but the traditional rules of grammar are never in poor style!

A grammar rule of thumb regarding the use of commas is to insert one at any point in the sentence where you would naturally pause while reading the sentence out loud. This method will not always produce a proper sentence, but will work most of the time.

Using Commas to Separate Sentence Elements
It's generally understood that commas are required to separate sentence elements in a series. Most writers understand this grammar rule. Whether or not to separate the last word or phrase of the series is a matter of opinion. Newspaper editors seem to prefer that the last comma (before the "and") is left out, but in academic literature the comma is usually included. Consider the media in which your article will be published, and if you have any doubt ask your editor which he/she prefers.

The zoo displayed lions, tigers, and bears. (literary style)

The zoo displayed lions, tigers and bears. (journalistic style)

My dog bolted out the door, ran across the yard, and continued down the street.

A series of only two words or phrases doesn't need a comma:

I bought a new jacket that is red and black.

We went to the movies and to dinner.

Using Commas to Separate Coordinate Adjectives
Separate coordinate adjectives with a comma, but leave it out when using non-coordinate adjectives. (Coordinate adjectives have equal status and can be interchanged without changing the meaning of the sentence; not so with non-coordinate adjectives). If the words and or but will fit between the adjectives, you need to use commas. For example, you could write: "The gruff, burly man scared the small children" OR "The burly, gruff man scared the small children." It would also be correct to write "The gruff and burly man scared the small children." But if you are writing about a little old lady, it would sound awkward if you wrote " an old little lady" or "a little and old lady."

Joining Independent Clauses with a Comma
Insert a comma and conjunction into the sentence when independent clauses are joined (independent clauses are sentence elements that can stand alone as simple, complete sentences):

My grandson ate a large meal, but he was still hungry. (My grandson ate a large meal. He was still hungry.)

I didn't care for the dish I was served, and I liked the dessert even less. (I didn't care for the dish I was served. I liked the dessert even less.)

Commas and Dependent Clauses
A dependent clause is not able to stand alone as a complete, simple sentence. When a dependent clause is followed by an independent clause, a comma should separate the two elements:

Running as swiftly as he was able, he barely missed his train.

Munching gleefully, the rabbit ate all my carrots.

Separating Parenthetic Elements with Commas
Use a comma to separate parenthetical elements of a sentence (elements that may be left out without changing the basic meaning of the sentence):

The covered bridge, which is over 150 years old, is falling down.

The town's newest restaurant, a diner that serves breakfast and lunch, isn't getting much business.

Commas and Introductory Elements
When your sentence has a brief introductory element, it may or may not require a comma, depending on the flow of the sentence. Longer introductory elements may require the use of a comma to make the sentence flow smoothly. If you're in doubt, add the comma and you will probably be correct.

By evening the rain had stopped. OR: By evening, the rain had stopped.

In the cool air of the evening, I wished I had brought my sweater.

Use Commas to Avoid Misreading
The correct use of a comma can prevent confusion when your sentence elements tend to merge:

Until spring, flowers will not bloom.

Outside, my dog was doing her morning business.

Other Comma Rules:
When a city and its country are mentioned together, use a comma after both the city and country, unless the possessive form is used:

My husband is in Las Vegas, Nevada, for a trade show.

Las Vegas, Nevada's casinos are a good place to lose money.

When a date in used in a sentence, a comma is required unless the specific day is not mentioned:

My youngest grandson was born on October 27, 2007.

My youngest grandson was born in October 2007.

Separate interjections from the rest of the sentence with commas. Interjections usually appear at the beginning of the sentence and express feeling or emotion. An exclamation point may be used instead of a comma to indicate a particularly strong feeling or emotion. Proper names may also be considered interjections:

Hey, stop stepping on my toes! OR: Hey! Stop stepping on my toes!

Oh, I don't know if I want to go with you.

Louis, stop pulling the dog's tail.

I told you, Alex, that I want you to wash the dishes.

Use commas to a separate quotation from the rest of the sentence, unless the quotation is preceded by the word that or is embedded in the sentence:

The sales clerk asked, "How may I help you today?"

"I've heard of snipe hunting," said Zachary, "but no one has ever taken me."

It is said that "to err is human."

It's polite to say "excuse me" when we bump into somebody.

Place a comma after common introductory expressions such as yes, well, and however.

Yes, I have a toothache.

Well, I really don't want to go to the dentist.

However, I'll go because I am in pain.

Well, there you go! Not too many rules to remember, I hope, and I'm sure I missed a few of the less common grammar rules concerning the use of commas. Correct comma usage is a skill that all writers need to master to deliver an accurate and easily understood message. If you still have doubts, there are many reliable online resources to help you; simply Google "correct use of commas." Or ask your editor!.