A common error with commas is to sprinkle them where they don’t belong. Here are five examples of this type of comma error.
Incorrect: The laptop on the table, is mine.
Correct: The laptop on the table is mine.
Do not separate a subject from its verb. The subject is “The laptop on the table.”
Incorrect: Motel rooms, that are dirty, ought to be illegal.
Correct: Motel rooms that are dirty ought to be illegal.
Do not set off a restrictive clause. The clause “that are dirty” is essential to the meaning of “motel rooms.” No commas are needed.
Incorrect: The dog understood at once, what his handler wanted.
Correct: The dog understood at once what his handler wanted.
Do not separate a verb from its direct object or complement. The clause “what his handler wanted” is the object of the verb understood.
Incorrect: Jethro wanted to be either a brain surgeon, or a fry cook.
Correct: Jethro wanted to be either a brain surgeon or a fry cook.
Do not use a comma to separate paired elements joined by coordinate conjunctions. The paired elements are “a brain surgeon” and “a fry cook.” No comma is needed.
Incorrect: The famous author lives in a small town, because she doesn’t like the noise of a big city.
Correct: The famous author lives in a small town because she doesn’t like the noise of a big city.
Do not set off an introductory independent (main) clause from a following dependent clause. “The famous author lives in a small town” is the main clause.
Note: if the dependent clause comes first, a comma is needed: “Because she doesn’t like the noise of a big city, the famous author lives in a small town.”