The comma is an important punctuation mark. The comma can serve several different purposes, but no matter how it functions within a particular sentence, it always creates a pause.
A reader must pause momentarily whenever a comma is encountered. However, it is important to keep in mind that all commas need a pause, but not all pauses need a comma.
Where to Use a Comma
Commas may only be used within a sentence.
Commas may not be used to begin a sentence. Commas are not terminal punctuation so they may not be used to end a complete sentence.
Comma Function and Comma Placement
As mentioned above, a comma can do many things:
- Separate a list of nouns
- Separate a list of adjectives
- Separate phases
- Separate subordinate clauses
- Precede a conjunction
- Offset an interjection
- Offset an appositive
A comma does not:
- Separate the subject from the predicate
- Follow the last item in a list
Commas That Separate
When a comma is used to separate a list of nouns the first comma should appear after the first item in the list. A comma should not come before the first item in the list.
Correct examples of commas separating a list of nouns:
- I packed my black dress, green bathing suit, and blue flip flops for the trip to the beach.
- Jack, Mike, and Chris went to the park yesterday.
- I'll have the salad, soup, and breadsticks for lunch.
Notice that there is a comma between each of the items in the list, however, there is no comma after the last item in the list.
The comma following the second to last item in each list, the comma preceding "and" in each of the above sentences, falls into a gray area. It is acceptable for the comma to be there because the comma functions as a separator within a list of nouns, however, the comma is not absolutely necessary. The best advice for whether or not to use the comma in questions is to follow the directions of the instructor, teacher, tutor, or style guide currently being used. It is most important to understand why the comma is appropriate and why it may be extraneous.
While the examples above all utilize nouns, commas may also separate a list of adjectives, phrases, or subordinate clauses:
- The black, white, and red polka dots give the purse a playful appearance.
- Today I need to empty the dishwasher, wash a load of laundry, and cook dinner.
- I wanted to go to the football game, but the tickets were too expensive.
Commas Before Conjuctions
Taking a closer look at the last example above, the comma precedes the conjunction "but."
In longer compound-complex sentences the comma before the conjunction is required, however, in shorter compound sentences the comma is not always required, although it is never wrong to place a comma before a conjunction.
Commas That Offset
Commas may also be used to offset interjections and appositives:
- Stop, don't take one more step!
- The car, a 1973 Volkswagon beetle, was painted a bizarre shade of yellow.
Comma Usage
The general rule of thumb is every comma gets a pause but not every pause gets a comma.
Learning how commas function and where commas should be placed within a sentence can greatly improve writing skills. Knowing how to properly use commas allows writers to craft sentences that are more easily understood by readers because commas separate larger parts of a sentence, items within a list, and multiple ideas within a sentence.
More Resources for Comma Usage
The Deluxe Transitive Vampire: A Handbook of Grammar for the Innocent, the Eager, and the Doomed by Karen Elizabeth Gordon (Pantheon; August 10, 1993)
The Elements of Style by William Strunk and E.B. White (Longman; September 3, 1999)
Eats, Shoots & Leaves: The Zero Tolerance Approach to Punctuation by Lynne Truss (Gotham; April 11, 2006)
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