Commas are horrible things. They confuse everyone. People just tend to throw them in whenever the sentence is getting too long, but you have to have a reason for a comma, and “too long” ain’t one of them. Here’s the rules:
- Between two complete sentences joined with a conjunction (subject/verb, and subject/verb). Yes, identify the subjects and verbs. Come on, you can do it. “He ate.” That’s a subject and a verb. Who and what.
- When you have several prepositional phrases at the beginning of the sentence (“On the first of the year before the party, we bought dresses”). I was taught to put one after two prep phrases, but I think that’s relaxed somewhat today.
- After a present participle phrase: “Sitting in the car, the girl looked in the mirror.” BUT make sure the subject of the second part matches the subject of the present participle phrase or you’ll have a dangling modifier: “Applying makeup, the boy couldn’t understand what was taking the girl so long.” The boy is not applying the makeup. The girl is. The boy would be watching the girl: “Watching the girl apply makeup, the boy …”
- In dialog, when one character is saying something to another and says the person’s name: “I love you, Jennifer.”
- Between a dependent clause and an independent clause: “When I smell that perfume, I want to throw up.” Remember, a dependent clause depends on the independent clause — think of it as leaning on the independent clause because it only has one leg and can’t stand alone. Repeat it out loud and see if it sounds complete: “When I smell that perfume …” Sound complete? No? Dependent. Use a comma afterward. (Not a period — that results in a sentence fragment.)
- Before the word “which”: “The dead man’s arm, which was …” I was taught not to use a comma before “that” because it’s a restrictive clause.