In fact, precise rules govern when to use this punctuation mark. When followed, they lay the groundwork for clear written communication.
We’ve compiled a list of all of the times when you need the mighty comma.
1. Use a comma before any coordinating conjunction (and, but, for, or, nor, so, yet) that links two independent clauses.
Example: “I went running, and I saw a duck.”
You may need to learn a few grammatical terms to understand this one.
An independent clause is a unit of grammatical organization that includes both a subject and verb and can stand on its own as a sentence. In the previous example, “I went running” and “I saw a duck” are both independent clauses, and “and” is the coordinating conjunction that connects them. Consequently, we insert a comma. See More . . .
Punctuation Must Be Parallel
When punctuation is parallel it means that interrupting a main clause with a dash or a comma requires using the same punctuation at the beginning and end of the clause.
Incorrect: The teenagers, students from Mrs. Smith’s art class—went on a field trip to the museum.
Correct: The teenagers, students from Mrs. Smith’s art class, went on a field trip to the museum.
Correct: The teenagers—students from Mrs. Smith’s art class—went on a field trip to the museum.
This rule also means that you should not use a semicolon to set off just one item in a list.
Incorrect: I have lived in Des Moines, Iowa, Seattle, Washington; and Boise, Idaho.
Correct: I have lived in Des Moines, Iowa; Seattle, Washington; and Boise, Idaho.
An Emdash is a Strong Comma
An emdash (the longest of the three dashes) can be used for many of the same purposes as a comma. A pair of emdashes can be used if the sentence already contains commas or to mark off information for emphasis; while a single emdash draws attention to a modifier or an extra piece of information.
Sarah hated walking to school—it was all uphill—but she had no choice, she had missed the bus again.
For his birthday, Mark received a sweater, a jacket, a savings bond—and a new bike!
Pizza, chocolate, and ice cream—these are my favorite foods.