Comma use

1. Series

I ate three tacos, eight burritos, fourteen enchiladas and drank ten glasses of water.

The contract calls for employee dimissal for use of narcotics while at the office, spending more than fifteen minutes in the bathroom at one time, or engaging in inappropriate behavior with customers.

2. Two independent clauses

The uprising continued in the campus community, but people will hopefully be calm on the mountaintop villa.

The judge fined the students $8,000 and ordered them to perform 400 hours of community service.

3. Introductory phrases

When he recognized that he had a severe illness, he left school and returned home to his parents.

At dinner we argued about politics.

4. Essential clauses

The ground beef that was labeled with numbers 112 and 114-H has been recalled by the state.

The three men who hijacked a bus died when they crashed.

5. Non-essential clauses

Jones, who turns 103 tomorrow, is wanted for assault with a deadly weapon.

Sierra Nevada Pale Ale, which has won many awards, is favored by many people.

6. Modifiers of equal rank

Can "and" be substituted?

It was a cold Midwestern night.

It was another cold, dreary Midwestern night.

The market featured frantic, irrational trading.

7. Parenthetical expressions

Where did it all go, she asked herself, the beautiful music of yesteryear?

8. Avoid confusion

Entering his office, laborer John was awakened by a loud noise.

9. Joining to complete thoughts with conjunction

With conjunction -- yet, for, and, nor, so, but -- linking two complete ideas (each with a verb and subject):

She wore a pink hat, but she didn't wear a pink dress.

My hamster loved to play, so I gave him a wheel to run on.