The comma is the most commonly used punctuation mark in standard written English. Yet, it is the most misused.
I have good news about commas and bad news. The bad news? Hundreds of rules regarding correct comma usage exist. The good news? You only need to know six of them for 99% of commercial writing purposes.
Rule #1: Use a comma with an introductory element, i.e., a word, phrase, or clause before the main part of a sentence. The element usually tells something about the main clause.
When the waltz was over, Ewan released his partner.
Once he produced an heir, his major responsibility to the family was over.
If Buddy cannot control his temper, he may lose his job.
Running as fast as she could, Maureen caught up to the suspect and threw him onto the ground.
Rule #2: Use a comma to set up a strong contrast. Potential hint words include but, yet, not, or never.
He admitted to strangling her, but not intentionally.
She was plagued by indecision, yet would act out impulsively.
Carmen, never the subtle flower, forced Lord Sagemore to her.
Wilma, not Betty, had the necklace made of rocks.
Rule #3: Use a comma before a coordinating conjunction (and, but, for, nor, yet, or, so) that joins two independent clauses.
Anne wants a life of freedom, but her father wants to use her as a pawn in marriage.
Beatrice’s hair smoked in the middle of dinner, and the sight brought tears to my eyes.
Tomorrow began his trial, so they hammered on his testimony all night.
The plant is called bleeding hear, for it’s poisonous to cattle.
Rule #4: Use a comma to separate consecutive words, phrases, and clauses.
Dedicated on a cold, raw day in January, the memorial soothed everyone’s hearts.
Carrie Ann’s closet was full of old, worn clothes.
We found the message scrawled on the garage door, beneath a window sill, and above the mantel.
Figure out how much the band trip will cost, how much time it will take, and how much fundraising it will require.
Exception: If one of the adjectives modifies another word in the series, do not separate them with a comma.
Mandy wore a bright blue gown.
Bright modifies blue.
Mandy wore a bright blue evening gown.
Bright modifies blue, and blue modifies evening gown. Note: evening gown is considered one thing, i.e., compound noun.)
Mandy wore an amazing, unique evening gown for the awards ceremony.
Amazing does NOT modify unique.
What about that pesky serial comma? No specific rule regarding this exists. Go with your personal preference.
That being said, sometimes a serial comma (sometimes referred to as an Oxford comma) is necessary to avoid confusion, usually with words used in pairs but set off as one item.
Desiring dinner on the train to London, Cecily noted all meals came with salad, soup, entrée, two vegetables, bread, ice cream and cake, and coffee.
Here, ice cream and cake are one dessert. So, to avoid confusion, a serial comma is necessary.
Rule #5: Use a comma around nonessential elements that could be removed without changing the meaning of the rest of the sentence.
Carmen, twice Argon’s age, refused a divorce.
Adrian wanted to run into the airplane propeller, an act that would have dramatically shortened his life expectancy.
Angie shoved Connie, who appeared restless, out the back door into the storm.
Bryant, who never expected to get caught, fainted when the guilty verdict was revealed.
Rule #6: Use a comma to set off dialog tags such as she said or he explained.
“Thomas confessed to the crime,” Roman said.
Blaise said, “Why don’t you join us?”
“You must have been moving at a pretty good clip,” Baz remarked.
“How,” Margaret asked,” can you always be so darn impulsive!”
Still not sure about when to and when not to use commas?
Try this: First, during the draft stage, read your sentences aloud or at least slowly enough so that an audience could easily understand you. As you read, place commas where you think they go—trust your instincts. Go ahead and put the commas where you “hear” them.
Then, go back and justify every single comma you used according to the rules listed here.
If you know the reasons to use commas and can’t think of a reason a comma should be there, leave it out.