A concise summary of comma rules:
(the safest rule: Don't use a comma unless you have a reason.)
Use commas between items in a list...
- using words: "Please pick up some rice, soy, and ginger at the store"
- using phrases: "You can open cans, slice carrots, and bake bread with this magical appliance!."
- using clauses: "I can't decide which classes to take, how I'm going to pay for it, or where I'm going to go."
Use commas in coordinate situations
Use commas after introductory elements in sentences
- Nouns of address: "Dave, I'm sorry I can't do that."
- Mild Interjections: "Well, I'm sorry I'm not going to be able to make it tonight."
- Groups of prepositional phrases: "In the house without anything to do, he stayed up all night noding."
- Participial words and phrases: "Regarding our research, please note our wonderful discovery."
- Infinitive phrases: "To set the server up, just follow the instructions on page 802."
- Subordinate clauses: "Soon after he saved his term paper, the power went out in the lab."
- Absolutes: "The matter already decided, he concluded to go about his business."
- Transition words and phrases: "First of all, I should explain my position."
Use commas to set off interrupting elements
- Nouns of address: "I'm very sorry, Mrs. Davies, but your hard drive can't be recovered."
- Appositives: "He bought a new car, a 1990 Honda Civic."
- Contrasting elements: "The software, not the hardware, is the problem in this case."
- Unnecessary descriptive phrases: "Iced tea, with or without lemon, goes great with chicken fried steak"
- Unnecessary descriptive clauses: "The core dump, which can sometimes be useful, won't be any help to us here."
- Absolutes: "Mark jumped at the sound of his alarm, its music blaring."
- Parenthetical expressions: "We will ship everything at once (e.g., hardware, software, documentation)".
Use commas in standard places
- Between parts of addresses in a sentence (but not zip codes): "1401 W. Airport Frwy., Euless, TX 76040"
- Between and after parts of a date: "Sunday, October 8, 2001"
- To set off direct quotations: "Thomas said, 'That's not true'."
- In a business letter after the close: "Sincerely,"
- In a personal letter after the opening and close: "Dear Frank, ....... Thanks,"
- Between and after titles: "Mark Smith, Jr., is the only son of Mark Smith, Ph.D."
- When reversing first and last names in a list: "Smith, Mark"
- To change a statement to a question: "You're the boss here, right?"
- In numbers: "123,456,789.00"
Source: Personal notes from High School English class.