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 comma use are, for the most part, firmly set, but there are a few gray areas. It’s helpful to know what they are so that you understand where you absolutely need a comma, where you absolutely shouldn’t put one, and also where you can fiddle around a bit.
1. Use a comma to separate items in a list of nouns. 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" (called the Oxford or serial comma), but it’s not necessarily incorrect to leave it out. It’s up to you. If you feel like a comma is needed there to avoid confusion, use one. If you prefer minimal puctuation and feel the sentence is readable without it, don’t use one.
2. In a string of two or more adjectives use a comma. If the adjectives come before the noun, don’t use “and.” You only need to use “and” in a list of adjectives if the list comes after the verb “to be.” Look at the following sentences:
I have a big, old, warm quilt on my bed.
The quilt on my bed is big, old and warm.
3. Don't separate a subject from its verb with a comma. Even if the subject is very long and you feel a comma is needed to allow the reader to pause for 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.
Betty walks to work every day, talks to clients, makes appointments, eats lunch, has afternoon meetings, and walks back home.
Just like in the first rule, the final comma (after “meetings”) is not necessary in a list of dependent clauses, but as the clauses get longer, leaving out that last comma can get confusing, so it is often better to put it in just to clear things up.
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.
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 one.
5. Use a comma to set off a non-defining subordinate clause or an appositive. 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 1972, is still New York’s tallest building.
The non-defining subordinate clause, “which was built in 1972” 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, 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.
6. Use a comma to set off expressions of contrast.
It was his money, not his looks, that first attracted me to him.
He doesn’t look for charm in a restaurant, but service.
7. Use a comma to set off a quote.
So she said to the guy, “Look, I don’t have to take this – not from you,” and then she turned and walked away.
“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.
Use a comma to set off a direct address.
The people are most grateful, Your Honor, for your years of continued service. "And I want to thank you, Ray Don, on behalf of all the women of the world, for your unfailing attention and concern."
8. Use a comma to signal that the main, independent clause is about to begin (when the sentence begins with something else) or that it is being interrupted. Words 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, in my opinion.
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 the other hand, did. If you have any doubts about this fact, please check her purse. You will find the gun there, I believe.
9. Use commas in addresses, dates and large numbers.
December 13, 2009
10. Use commas in the salutation and the closing expression of a letter.
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 10 comma rules, your writing will be neater, clearer and perfectly acceptable to English teachers everywhere, no matter where they stand on the gray areas.