Comma: Yes
- Before a coordinating conjunction (and, but, or, nor, so, for, yet) to connect independent clauses (complete sentences). Ex: He frowned, but she did not understand why he was worried.
- After most introductory words, phrases, or clauses. Ex: After the noisy party, the neighbors complained.
- To set off extra information included in the sentence. Ex: My father, a computer programmer, works late at night.
- To set off a transitional expression. Ex: The ending, however, is disappointing.
- To separate three or more items in a series. Ex: the fans applauded, cheered, and whistled.
- Between coordinate adjectives. Ex: We ate a delicious, well-prepared, and inexpensive meal.
- After a verb that introduces a quotation. Ex: She gasped, "We haven't a moment to lose!"
- To clarify meaning. Ex: Of the gymnastic team's twenty, five were injured.
Comma: No
- Not between subject and verb. Ex: The man in the baggy pants is her English teacher. (Some writers will be tempted to place a comma before the verb is)
- Not before part of a compound structure that is not an independent clause. Ex: She won the trophy and accepted it graciously. (The and is not linking two independent clauses, or complete sentences, so it does not call for a comma.)
- Not after a coordinating conjunction connecting two independent clauses but before it. Ex: The movie tried to be engaging, but it failed miserably. (Writers often misplace these commas).
- Not between two independent clauses without a coordinating conjunction. Use either a period, creating two sentences, or a semi-colon instead. Using a comma creates what is known as a comma splice. Ex: He won; she was delighted.
- Not before a clause beginning with that. Ex: They warned us that the meeting would be difficult. (Some writers will be tempted to place a comma before "that").
- Not before and after essential information. If it is information necessary for the sentence meaning to be clear, commas are not necessary. Ex: The player who scored the goal became a hero. (If the fact that he scored a goal is omitted, or separated by commas, we do not understand why he became a hero).
- Not between a verb and its object or complement. Ex: The best gifts are food and clothes. (Some writers may be tempted to place a comma after "are").
- Not after "such as" or "including." A comma may be called for before such words if surrounded by a complete sentence. Ex: Popular fast food items, such as hamburgers and hot dogs, tend to be high in fat. (Commas are only used to set apart the additional information).
