Commas join, emphasize, contain, and separate.
- They work with a coordinating conjunction to join two independent clauses within a sentence.
Example: Latoya threw the basketball, and it sailed through the net.
- They emphasize introductory elements at the beginning of a sentence or clause.
Example: Humiliated, she fled he diner.
- They set off cumulative elements at the end of a sentence or clause.
Example: Nine senators changed their vote, passing the bill.
- They work in pairs to contain restrictive modifiers within a sentence.
Example: The committee, heading by Dr. Suarez, met weekly to develop a budget.
- They work in pairs to contain parenthetical expressions within a sentence.
Example: The candidate, much to the committee’s surprise, voluntarily revealed her position on several key controversies.
- They separate a dependent clause at the beginning of a sentence from the independent clause following it.
Example: When it started to rain, Sue wished she had her umbrella.
- They separate two or more adjectives that independently describe the same noun.
Example: An open, exploratory, and inclusive spirit marked the meeting.
If you can put the word “and” and it makes sense, the comma usage is correct.
- They separate quotations from their attributions.
Examples: “Politics is the art of looking for trouble, finding it everywhere, diagnosing it incorrectly, and applying the wrong remedies,” said Groucho Marx.
“In a time of universal deceit,” writes George Orwell, “telling the truth becomes a revolutionary act.”
- They separate items in a list.
Example: The position requires expertise in building consensus, formulating policy, and developing long-term goals.
The final comma, the one before “and” or “or,” is known as the Oxford comma, Harvard comma, or serial comma. The Oxford comma should always be used where it is needed to avoid confusion (for example where one or more items in the list already include the word “and”). Otherwise it is optional.
Commas also separate elements in dates, numbers, personal titles, and addresses.
Use commas to separate the day of the week from the month and to set off a year from the rest of the sentence.
- On Friday, February 13, 2015, we will be having our annual Valentine’s Day dance.
- On December 12, 1890, orders for the arrest of Sitting Bull were sent.
- Graduation is set for May 20, 2016.
You do not need to use a comma when giving only the month and the year:
- The next presidential election will take place in November 2016.
Use commas to separate numbers into groups of three when they are more than four digits long. The comma is optional when the number is four digits long:
- 2,400 (or 2400)
Do not use a comma in street numbers or page numbers.
- The table appears on page 1397.
- The fire occurred at 5509 Avenida Valencia.
When following a name with a title, use a comma (if the title is at the end of the sentence) or two (if the title is in the middle of the sentence) to separate the title from the rest of the sentence.
- Earnings far exceeded projections last quarter according to Hitomi Masamura, vice president.
- Paul Hjort, D.C., practices chiropractic medicine in Flagstaff.
Separate each element of an address with commas. However, do not use a comma before a ZIP or other postal code.
- Lady Gaga performed in Phoenix, Arizona.
- Write to the program advisor at 18401 N. 32nd Street, Phoenix, Arizona 85032.
While there are many different ways to use commas in writing, most comma usages fall into three situations. If you know the basic rule for these three cases, you should be set for comma usage.
- Put a comma before a coordinating conjunction (for, and, nor, but, or, yet, so) that separates two independent clauses.
Example: I wanted to drive to the mall, but my car wouldn't start.
- Put a comma after introductory words, phrases, or clauses in a sentence.
Example: Although it was a good offer, I felt that I needed to explore other options.
- Use commas to set off elements that interrupt or add information in a sentence.
Example: Tommy, my older brother, loved to punch me for telling his secrets.