English Comma Usage

Source: http://owl.english.purdue.edu/handouts/grammar/g_comma.html
Rules for using commas in English:

1. Use commas to separate independent clauses when they are joined by a coordinating conjunction: and, but, for, or, nor, so, yet.

Example: The game was over, but the crowd refused to leave.

Yesterday was her brother’s birthday, so she took him out to dinner.

2. Use commas after introductory clauses, phrases, or words that come before the main clause.

Common introductory clauses begin with: after, although, as, because, if, since, when, while

Examples: While I was eating, the cat scratched at the door.

Because her alarm clock was broken, she was late for class.

If you are ill, you should see a doctor.

When the snow stops falling, we’ll shovel the driveway.

Common introductory words that should be followed with a comma: well, yes, however

Example: Well, I guess I should study for the test.

Yes, the package should arrive tomorrow.

However, you may not be satisfied with the results.

3. Use commas to separate clauses, phrases, and words that are not essential to the meaning of the sentence. Use one comma before to indicate the beginning of the pause and one at the end to indicate the end of the pause.

Ask these questions to determine if the clause is essential:
• If you leave out the clause, phrase, or word, does the sentence still make sense?
• Does the clause, phrase, or word interrupt the flow of words in the original sentence?
• If you move the element to a different position in the sentence, does the sentence still make sense?

Examples:

That Tuesday, which happens to be my birthday, is the only day when I’m available to meet.

The service at this restaurant is great. The food, on the other hand, is terrible.

I appreciate your help. In this case, however, I think you helped too much.

4. Use commas to separate three or more words, phrases, or clauses in a series.

Example: At the store I bought eggs, bread, milk, chicken, and crackers.

When you have a list within a list, you use semicolons.

Example: At the store I bought eggs; bread, wheat, rye, and white; milk; chicken; and crakcers.

5. Use commas to separate two or more adjectives that describe the same noun.

As a test you can ask yourself these questions:
• Does the sentence make sense if the adjectives are written in reverse order?
• Does the sentence make sense if the adjectives are written with and between them?

Example:

He was a difficult, stubborn child.

Your cousin has a pretty, happy smile.

6. Use commas to separate contrastive elements in a sentence or to indicate a distinct pause or shift.

Example: He was only ignorant, not stupid.

You’re one of the senator’s close friends, aren’t you?

7. Use commas at the end of a sentence that refer back to the beginning or middle of the sentence. Such phrases can be placed anywhere in the sentence without causing confusion.

Example: Nancy waved enthusiastically at the docking ship, laughing joyously.

Laughing joyously, Lisa waved at Nancy.

Lisa waved at Nancy, who was laughing joyously.

8. Use commas to set off all geographical names, items in dates (except the month and day), addresses (except the street number and name), and titles in names.

Example: Davis, California

January 16, 2009

1600 Pennsylvania Avenue, Washington D.C.

Rachel B. Lake, MD.

9. Use commas with quotations.

Example: John said, “I’ll see you tomorrow.”

“I was able,” she answered, “to complete the assignment.”

In 1848, Marx wrote, “Workers of the world, unite!”