The comma is the most commonly used and abused punctuation mark. People often insert commas between subject and verb or when they reach the end of a thought, without regard for the rules of comma usage.
Commas are used to separate words or groups of words in a list or parallel construction; to set off introductory elements, interruptions, and words moved from their usual position; and to coordinate such grammatical structures as compound predicates, coordinate adjectives, and descriptive appositives and modifiers. On the other hand, some comma uses have little to do with the meaning of a sentence and are inserted to prevent misreading or to create emphasis. In a few cases, they simply represent tradi- tional ways of punctuating various grammatical elements.
This section discusses some of the more common uses and abuses of this often troublesome punctuation mark.
Commas separate items in a series. The items can be single words, phrases, or clauses. Although current practice allows the final comma to be dropped before the final conjunction (or, but, nor, and and), including the comma can avoid possible confusion for the reader.
- We brought sandwiches, wine, cold soup, and chocolate cake on the picnic.
- The conductor set up his stand, took out the score, and lifted his baton. (verb phrases)
- She is vice president of operations, sales and resources and personnel. (Are the final categories sales and resources, and personnel or are they sales, and resources and personnel? A final comma would make the categories clear.)
When two independent clauses are joined by and, but, or, nor, or for, use a comma before the conjunction. However, no comma is needed if the clauses are very short.
- Her gymnastics routine was brilliant, and the judges gave her a 99.46.
- Yolanda knew we’d be late, but she left anyway.
- He can play the guitar, or he can do his magic show.
- Stir the batter and add the eggs slowly.
- They came early and they stayed late.
A comma is not used when and, but, for, or, or nor joins two verbs that share the same subject.
- Kerry Wood pitches with the best of them and bats better than most outfielders.
- Shelly has never cooked a meal nor washed her own clothes.
Introductory Clauses, Phrases, Expressions
Use a comma after introductory phrases or clauses unless they are very short. When expressions such as no, yes, in addition, well, and thus begin a sentence, they are followed by a comma.
- When Ansel Adams took a photograph, he knew exactly what would appear in the picture.
- Speaking of food, isn’t anybody hungry?
- In summer we always try to get outside more. (Short phrase in summer does not require a comma.)
- Well, losing one game doesn’t ruin an entire season.
- Thus, I feel your qualifications make you perfectly suited for this job.
Nonrestrictive Clauses and Nonessential Material
Commas set off nonrestrictive clauses and expressions that interrupt the sentence or that add incidental information or description.
- The rodeo, always held in August, draws tourists from all over. (Always held in August is a nonrestrictive clause.)
- We wanted to finish, of course, but didn’t know how.
- The new officer, I’m sure you remember him, locked himself out of his car.
Words used in direct address are set off by commas regardless of their posi- tion in the sentence.
- Greg, can you fix my e-mail?
- They heard about the trouble, Jean, and wanted to help.
- Please sign this receipt, Ms. Liang.
Commas and Clarity
At times commas are used to avoid confusing the reader when a sentence can be read in more than one way.
- In autumn nights grow steadily longer. (On first reading, autumn and nights appear to go together. It’s evident from the rest of the sentence, however, that they are separate. A comma after autumn would make the meaning clear immediately.)
- In autumn, nights grow steadily longer.
Traditional Comma Uses
Commas are used in certain conventional situations including dates, addresses, the salutations and closings of informal letters, and certain forms of proper names or names followed by a title.
- We were married June 22, 1941, in Los Angeles. (When only the day and month are used, no commas are necessary. We were married on June 22 in Los Angeles.)
- Send your rebate coupon to Harvard House, Suite 2920, 467 West Rhine Street, Portland, Oregon.
- Dear Harriet,
- Sincerely yours,
- Truly yours,
- Samuel Stanislaw, Jr. (but Samuel Stanislaw III) Judith Gallagher, PhD
- Linda Marks, director
Many people use commas incorrectly. The following guidelines point out common errors in style.
- Never use commas to separate subject and verb.
- Incorrect: Finding a lead singer for the band, has been an ordeal. (The noun phrase Finding a lead singer for the band is the subject and should not be separated from the verb has been.)
- Correct: Finding a lead singer for the band has been an ordeal.
- Never use commas to separate two phrases or subordinate clauses joined by a conjunction.
- Incorrect: The waiter suggested that we order a white wine, and that we try the Cajun appetizers.
- Correct: The waiter suggested that we order a white wine and that we try the Cajun appetizers.
- Incorrect: Ming-Jie painted her room, but not the hallway.
- Correct: Ming-Jie painted her room but not the hallway.
- Incorrect: After the treaty was signed, both sides pulled back their troops, and reduced their armored divisions.
- Correct: After the treaty was signed, both sides pulled back their troops and reduced their armored divisions.
- In a series, never use a comma to separate a modifier from the word it modifies.
- Incorrect: They drove through a damp, cold, eerie, fog.
- Correct: They drove through a damp, cold, eerie fog.
- Incorrect: That is a ridiculous, immature, wicked, suggestion.
- Correct: That is a ridiculous, immature, wicked suggestion.