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Comma usage can be tricky for writers. The following rules will help writers understand when commas are necessary.
1. Commas are needed to separate items in a list or series. These items can be nouns, verbs, adjectives, adverbs, phrases, or clauses. (When creating lists, items should have the same grammatical structure to keep the list parallel. For example, a list should contain three nouns instead of two nouns and one verb.)
--I bought oranges, milk, bread, and pasta.
--Toby plays soccer in the fall, wrestles in the winter, and plays baseball in the spring.
--The running back sprinted toward the sideline, down the field, and into the end zone.
--Doing homework, getting to class on time, and studying for tests are necessary to pass the class.
--Jamal vacuumed the floor, Kiesha dusted the furniture, and Maurice washed the dishes.
2. A comma and a coordinating conjunction are
needed to separate two independent clauses in
--Willy read the book, but he did not
--Quincy needs to be home by nine, or he will be grounded.
--Nasri saved her money, and she bought a computer.
A comma is not needed to separate two verbs in a simple sentence.
--I cleaned the house and cooked dinner.
--The professor explained the assignment and answered questions.
Compare the following correctly-written sentences.
--Willy read the book, but he did not understand it. (compound sentence)
--Willy read the book but did not understand it. (simple sentence)
3. A comma is needed after an introductory element such as
an introductory dependent clause
--Because Mohammed has to travel frequently for work, he hired Gene to mow the lawn in the summer and shovel the driveway in the winter.
--Although both of his parents went to the University of Iowa, Raul plans to attend the University of Minnesota.
an introductory adverb
--Quietly, Joe closed the baby's door.
--First, you need to melt the butter.
--Kendra studied hard for the test. However, she did not pass it.
an introductory prepositional phrase
--From Minneapolis, we drove to New York.
--With a steady hand, the surgeon operated.
--Amina plays many sports. For example, she plays tennis, volleyball, and basketball.
an introductory present participial phrases
--Watching television late into the night, Milika neglected her homework.
--Sprinting down the court, Ansel twisted his knee.
an introductory past participial phrase
--Locked out of his house, Stuart waited at his neighbor's house until his parents returned home.
an introductory absolute phrase
--Their children asleep, Demarcus and Mary watched a movie.
--His car in the shop, Keith took the bus to work.
4. Commas are needed to set off elements that interrupt independent clauses. Many of the elements above can interrupt independent clauses.
--Mohammed, because he has to travel frequently for work, hired Gene to mow the lawn in the summer and shovel the driveway in the winter.
--Amina plays many sports. She, for example, plays tennis, volleyball, and basketball.
--Milika, watching television late into the night, neglected her homework.
--Rosa, finished with her math test, worked on her history homework.
--Demarcus and Mary, their children asleep, watched a movie.
5. Commas are needed to set of parenthetical or non-essential elements. Unlike essential elements, non-essential elements can be removed without changing the overall meaning of a sentence. Non-essential elements are important details, but the essence of sentences remain intact without them. It is sometimes tricky to decide if an element is essential or non-essential. Basically, if the element is not necessary to understand the word it describes, the element is non-essential.
--Central High School, which is right next to Interstate 94, has a strong International Baccalaureate program.
Since the subject, Central High School, is understood without the relative clause, the relative clause is non-essential.
--The high school that is right next to Interstate 94 has a strong International Baccalaureate program.
Since the subject, the high school, is not understood without the relative clause, the relative clause is essential.
--Professor Giles, who has taught creative writing for twenty years, plans to retire soon.
Since the subject, Professor Giles, is understood without the relative clause, the relative clause is non-essential.
--The professor who has taught creative writing for twenty years plans to retire soon.
Since the subject, the professor, is not understood without the relative clause, the relative clause is essential.
appositives are usually non-essential.
--Jason's house, a two-bedroom bungalow near the city, was built in 1948.
--Doug bought his car, a silver Toyota Camry, from a dealership in Chicago.
--Molly, my wife, worked in banking before getting her teaching license.