8.10 Punctuation: Commas
When it comes to using commas, you have likely heard the guideline to ‘place a comma wherever there’s a pause.’ This advice is helpful to a degree, but it’s important to understand some of the rules that govern that advice. However, it can seem daunting as a writer to learn and apply the seventeen or so rules for comma usage, so we’re only going to look at a few of the most common ones. It’s helpful to remember the comma’s primary function: it separates. The comma separates complete ideas, descriptive phrases, items in a list, and before and after most transition words.
RULE 1. Use commas to separate independent clauses when they are joined by any of these seven coordinating conjunctions: for, and, nor, but, or, yet, so (FANBOYS). The comma comes after the first clause and before the conjunction.
EXAMPLES:
| The game was over, but the crowd refused to leave. |
| The student explained her question, yet the instructor still didn’t seem to understand. |
| Yesterday was her brother’s birthday, so she took him out to dinner. |
RULE 2. Use commas after introductory clauses, phrases, and words that come before the main clause.
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- Introductory clauses:
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EXAMPLES:
| While I was eating, the cat scratched at the door. |
| Because her alarm clock was broken, she was late for class. |
| If you are ill, you ought to see a doctor. |
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- Introductory phrases (note how the main subject and verb follow the comma):
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EXAMPLES:
| Having finished the test, he left the room. |
| To get a seat, you had better come early. |
| After the test but before lunch, I went jogging. |
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- Introductory words:
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EXAMPLES:
| Well, perhaps he meant no harm. |
| Yes, the package should arrive tomorrow morning. |
| However, you may not be satisfied with the results. |
RULE 3. Use commas in the middle of a sentence to separate nonessential clauses, phrases, and words. Use one comma before to indicate the beginning of the pause and one at the end to indicate the end of the pause.
EXAMPLES:
| Clause: | That Tuesday, which happens to be my birthday, is the only day when I am available to meet. |
| Phrase: | The food, on the other hand, is rather bland. |
| Word: | This time, however, you seem to be falling behind. |
*NOTE: To determine if a clause, phrase, or word is essential, ask yourself if the sentence still makes sense if you leave it out. If it does, then it’s nonessential and should be set off with a pair of commas. Nonessential elements are sometimes called parenthetical.
RULE 4. Use commas to separate three or more words, phrases, or clauses written in a series.
EXAMPLES:
| The Constitution establishes the legislative, executive, and judicial branches of government. |
| The candidate promised to lower taxes, protect the environment, reduce crime, and end unemployment. |
*NOTE: The comma before the and at the end of a list is called an Oxford Comma; some writers choose to leave off the final (Oxford) comma in a series. For example, in both of the sentences above, the last comma could be left off and still be correct (just be sure to be consistent in your usage).
RULE 5. Use commas to separate two or more coordinate adjectives that describe the same noun. Coordinate adjectives are adjectives with equal status in describing the noun.
EXAMPLES:
| He was a difficult, stubborn child. (coordinate adjectives) | |
| Your cousin has an easy, happy smile. (coordinate adjectives) | |
| They lived in a white frame house. (*non-coordinate adjectives, so no comma) |
*NOTE: To determine if two adjectives are coordinate, ask yourself if the sentence still makes sense if you reverse the order of adjectives or put and between them. If so, then it needs a comma. For instance, in the example above, a white frame house wouldn’t make sense if we wrote instead, a frame white house or a white and frame house.
RULE 6. Use commas to indicate speech or a quotation.
EXAMPLES:
| John said without emotion, “I’ll see you tomorrow.” |
| “I completed the assignment,” she answered. |
| According to E.B. White in The Elements of Style, “When you say something, make sure you have said it.” |
A FINAL RULE to consider is to use commas wherever necessary to prevent possible confusion or misreading.
EXAMPLE:
| To George, Harrison had been a sort of idol. (*the comma here eliminates potential misreading of George Harrison, the late guitarist for The Beatles.) |
| Let’s eat, Grandma. (*the comma here saves Grandma from being eaten.) |
As you read, revise, and edit your writing, do so with comma correctness in mind. It’s also important to remember that commas have much to do with sentence structure and wording, which is always in the writer’s control.
Take the following short quiz to test your knowledge of comma rules and correct comma usage:
Additional Resources
- “Notes on Punctuation,” a guide from writer Lewis Thomas on using commas effectively and how to word a lengthy sentence without overusing commas
- “Punctuation Matters,” a guide from Technical Writing Essentials.
