14 rules to follow when deciding whether to use a comma
1) If a dependent clause comes at the beginning of the sentence, use a comma after the phrase or clause. This can be tricky because the exact same words don’t need a comma if they come at the end of a sentence.
Correct: Because you’re hungry, I’ll make you a snack.
Incorrect: I’ll make you a snack, because you’re hungry.
In this case, because you’re hungry is the dependent clause. I’ll make you a snack is the independent clause. When the independent clause comes first, there’s no need for a comma. If the dependent clause comes first, you do need one.
2) Whenever you have a list of three or more words, phrases, or clauses, you should use a comma to separate them. It’s up to you to decide whether you want to add a final comma before the word “and” or “or” in your list. Keep in mind that the serial comma, also known as the Oxford comma, has both admirers and critics. Be sure to check with your favorite style guide and make a decision before you write your list. Whatever you decide, be ready for someone to disagree with you!
I study the diet of carnivorous bats, the sleeping habits of nocturnal possums, and the movement of field mice.
I study the diet of carnivorous bats, the sleeping habits of nocturnal possums and the movement of field mice.
I study the diet of carnivorous bats the sleeping habits of nocturnal possums and the movement of field mice.
Notice that the first correct sentence has an Oxford comma. The second sentence omits it. Whichever option you choose, be consistent. Don’t include a serial comma in one paragraph and then omit it in the next.
3) Two independent clauses need a comma when they are connected by a coordinating conjunction. Keep an eye out for the following connectors: and, but, for, or, nor, so, or yet.
Correct: I am hungry, and I am going to eat.
Incorrect: I am hungry, and tired.
Incorrect: I am hungry, I am going to eat.
In the first sentence, the word “and” acts as a coordinating conjunction separating two main clauses. Both I am hungry and I am going to eat could stand alone as independent sentences. On the other hand, tired is not an independent clause, so there’s no need to add a comma before the conjunction in the second example.
In the third sentence, there’s no coordinating conjunction. Without the word “and,” you would need a semicolon or a period to separate two independent clauses. If you tried to replace those punctuation marks with a comma, you’d introduce an error called a comma splice.
4) Use commas to mark a parenthetical or interruption. Ask yourself whether the phrase or description has anything to do with the rest of the sentence. Does it contain essential information needed to understand the meaning of the sentence? If not, you may need commas to set it apart from the rest.
Correct: We traveled by ship, even though Margaret prefers flying, across the ocean and into a deep bay.
Incorrect: We traveled by ship, even though Margaret prefers flying across the ocean and into a deep bay.
The two sentences above have very different meanings. In the first example, the phrase even though Margaret prefers flying is a nonessential addition to the sentence. In the second example, the reader might infer that Margaret wants to fly into a deep bay. What a difference one comma makes!
5) Set off direct quotations with a comma. Be sure to refer to your favorite style guide once again! Different style manuals advocate variations in punctuation, but it’s typical to see a comma used in the following way.
Correct: “I love commas,” he said.
Incorrect: “I love commas” he said.
Incorrect: He told me that he “loves,” commas.
Use a comma to separate the quotation from the attribution. If you’re using quotation marks around a word or phrase that fits within the syntax of a longer sentence, you don’t need to use a comma.
6) Use a comma with coordinate adjectives, two or more adjectives that describe the same noun. Neither of the adjectives should modify the other; instead, both should describe the noun.
Correct: He has a red, four-bedroom house.
Incorrect: He has a bright, red car.
In the first sentence, both red and four-bedroom describe the house. The second example involves an adjective modifying another adjective, so there’s no need for a comma. Because the word bright modifies red, these words are non-coordinate adjectives.
7) Add a pair of commas around an appositive. You can think of an appositive as a word or phrase that renames a noun or pronoun. Usually, it appears right after the noun or pronoun in question.
Correct: My science professor, Mr. Winslow, teaches on Tuesdays and Wednesdays.
Incorrect: My science professor, teaches on Tuesdays and Wednesdays.
You only need commas when you’re renaming the noun. Of course, you don’t have to literally use a name. In the correct sentence above, you could replace Mr. Winslow with another descriptive phase, and you would still need two commas.
8) Use a comma, or a pair of commas, to set a conjunctive adverb apart. Some conjunctive adverbs include indeed, instead, likewise, finally, and however.
Correct: Finally, I learned to tie my shoes.
Correct: I learned to tie my shoes, finally, after many years of effort.
Incorrect: I learned to tie my shoes; finally, after many years of effort.
A conjunctive adverb should be set off by two commas when it appears in the middle of the sentence. You should only introduce a semicolon if two independent clauses flank the conjunctive adverb. In the example above after many years of effort is not an independent clause, so a semicolon would be inappropriate.
9) Include a comma in numbers above 999. Also, use a comma when writing the date in American formatting.
Correct: August 8, 1985
Incorrect: 8, August 1985
If you write the date so that the day of the month comes first, you don’t need to use a comma.
10) Commas should separate the names of cities and states or countries.
Correct: Denver, Colorado
Incorrect: Denver Colorado
11) Use a comma before a question tag, a short phrase added to the end of the sentence to turn it into a question.
Correct: You like New York, don’t you?
Incorrect: You like New York don’t you?
Comma use alerts the reader that he or she should pause after New York.
12) When you address someone, use a comma.
Correct: Elizabeth, I hope you understand.
Incorrect: Elizabeth I hope you understand.
Again, a comma helps to avoid confusion. It’s clear that you’re addressing Elizabeth in the first example; whereas, in the second example, your readers won’t know where to pause.
13) Use commas around a nonrestrictive clause, which gives inessential information. Often, a nonrestrictive clause begins with who, which, or such as. If you omit the clause, nothing else about the sentence would need to change.
Correct: The study, which lasted for three years, proved that the medicine worked.
Incorrect: The study which lasted for three years, proved that the medicine worked.
If the nonrestrictive clause appears at the beginning of the sentence, you place a comma after it. When a nonrestrictive clause concludes a sentence, include a comma before the clause.
14) You can use a comma with an introductory phrase or word. Introductory words include transitions like meanwhile, later, and furthermore. Introductory phrases may include prepositional phrases, participial phrases, and adverbial phrases.
Correct: Later, I managed to find a phone.
Correct: After the movie ended, I managed to find a phone.
Incorrect: On the floor, sat the puzzle.
If you’re using an introductory phrase that’s less than four words, you may choose to include the comma or omit it. If the phrase is more than four words, you definitely need a comma. There’s one tricky exception to remember. Never use a comma after an introductory phrase that’s immediately followed by a verb. The incorrect example above does not need a comma because the verb sat comes directly after the phrase.
Tips for Remembering the Rules
To conclude, the rules around comma usage may seem complicated. We’ve listed a large number of situations and exceptions you’ll need to remember. Still, it’s worth learning how to use a comma properly. By including commas only where they belong, your writing will become clearer and easier to read. Don’t be intimidated! Start off slowly by eliminating the commas that you don’t need.
After you’ve eliminated unnecessary commas, decide whether you love or hate serial commas. Will you use them when you write lists? Next, you can move on to memorizing the coordinating conjunctions. After that, learn how to recognize prepositional phrases, conjunctive adverbs, and coordinate adjectives. Focus on one rule at a time, and you’ll be a grammar expert before too long. At the very least, you’ll know when it’s appropriate to use a comma!
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