Comma rules can be confusing, not necessarily because they're difficult, but because people often disagree on what they are. One teacher may tell you one rule for using commas while another may tell you the opposite, and the frustrating truth is that they're probably both right.
The rules for when to use commas and when not to use them are, for the most part, firmly set. However, there are still a few gray areas. It's helpful to know what they are so you understand where you absolutely need a comma, where you absolutely shouldn't put one, and also where you can fiddle around a bit.
If you have more than two nouns, you need to separate them with commas. In a list of nouns, you will also separate the final two with the word "and" or the word "or" like this:
Janet went to the store to buy pasta, broccoli, lemons, and beans.
Most people consider it correct to include a comma after "lemons" in the example above. Called the Oxford or serial comma, this final comma is a topic of hot debate and some people prefer to leave it out. That isn't necessarily incorrect.
If you feel like a comma can help to avoid confusion, use one. If you prefer minimal punctuation and feel the sentence is readable without it, don't use one. Of course, always refer to your style guide, as it may have differing guidelines.
I have a big, old, warm quilt on my bed.
The quilt on my bed is big, old, and warm.
Even if the subject is very long and you feel a comma is needed to allow the reader to pause for a breath, don't do it.
The president of the largest company in North America and his most trusted and esteemed board of advisors (no comma here) wish to see you immediately.
Here are 8 Times Commas Were Important!
As in the first rule, the final comma is not necessary in a string of dependent clauses. However, as the clauses get longer, leaving out that last comma can get confusing, so it is often better to put it in just to keep things clear:
Betty walks to work every day, talks to clients, makes appointments, eats lunch, has afternoon meetings, and walks back home.
When your clauses are independent (they could stand alone as complete sentences), it is absolutely necessary to use both the comma and the "and" before the final clause:
Betty gets home at 5:30, she and her husband have dinner together, they watch TV for a few hours, and they go to bed around 11:00.
A non-defining subordinate clause gives some information about a noun, but the information is not necessary for identifying that particular noun. These clauses usually begin with "which" or "who."
The Empire State Building, which was built in 1930, is still New York's tallest building.
The non-defining subordinate clause, "which was built in 1930," gives some information about the Empire State Building, but we don't need that information to identify the building or distinguish it from any other Empire State Buildings. It's just extra information.
An appositive is similar to a non-defining subordinate clause, but it doesn't include "which" or "who." It's a word or phrase that can be substituted for a name.
Bob Vance, the president of Vance Refrigeration, married my coworker Phyllis.
Here, you could identify Phyllis's husband as either "Bob Vance" or "the president of Vance Refrigeration." They are the same person.
You will notice that short or one-word appositives, such as in the phrase "my coworker Phyllis" do not have to be set off with commas. If you think a sentence or phrase would be clearer by setting off a short appositive with commas, then, by all means, do it. However, it is not absolutely necessary.
Any time you need to offset a clause and provide additional information, be sure to place a set of commas around the clause:
It was his money, not his looks, that first attracted me to him.
He doesn't look for charm in a restaurant, but service.
It's best to use a comma after please, a direct address, or to set off a quote:
"Please," he begged, "can't we just talk about this?"
She stopped and turned around slowly. "It's too late," she replied. "You had your chance."
I want to thank you, Ray Don, on behalf of all the women of the world, for your unfailing attention and concern.
In the words of Martin Luther King Jr., "The time is always right to do what's right."
If you're writing an informal piece and starting your sentence with "but," it's best to use a comma after it. Likewise, if you're adding a clause after "which," you'll need a comma after it as well. "Also" works in the same way. If you're adding more information, a comma after "also" will set things up nicely too.
But, that's beside the point. She's going to leave in the morning.
She told me he was coming which, let's be honest, is total hogwash.
Also, I think she's a habitual liar.
Words or phrases that may be used to introduce or interrupt a sentence include: in fact, on the other hand, to tell the truth, yes, no, indeed, well, nevertheless, however, and in my opinion.
These words and phrases indicate that you're about to present an important fact or idea. That's why we need to add a comma after them to introduce the idea and signal a slight interruption in the sentence. For example:
The truth, in my opinion, is that we are all guilty in part. Indeed, I know that I am. However, I didn't pull the trigger. Mrs. Peacock, on the other hand, did. If you have any doubts about this fact, please check her purse. You will find the gun there, I believe.
When listing a city and state, a comma is required to separate the two. As for dates, a comma is required between the day of the month and the year. Numbers also require a comma after every third digit from the right.
December 13, 2009
In the salutation of a letter, a comma is needed after the person's name:
Dear Aunt Carol,
If you're writing a formal business letter, you might substitute a colon (:) for the comma in the greeting.
Dear Mr. Jones:
The closing, however, will always use a comma.
If you can master these comma rules, your writing will be neater, clearer and perfectly acceptable to English teachers and grammar purists everywhere, no matter where they stand on the gray areas.
To conclude your comma mastery, study these examples of comma splices to learn how to avoid the common error.