Ah, the comma. Along with the period, it is one of the most commonly used forms of punctuation. But commonly used does not always transfer to correctly used. Commas can be tricky and knowing when to use them, and when not to, is important. Commas serve a variety of purposes. A comma is used to indicate a pause and allows a reader or speaker to catch their breath. Commas are also used to separate words or word groups in lists of three or more things. Commas are really important. Using commas correctly is even more important. Here are some uses for commas:
Commas are used to separate geographical locations, such as city, state or city, country.
Phoenix, Arizona, USA
Lake Mead, Nevada
When they are embedded in a sentence, you’d put a comma after the state or country, too.
Phil is from the Phoenix, Arizona, area.
We drove through Sioux Falls, South Dakota, and it was beautiful!
Commas are used in dates to separate the day and month from the year. Try saying the date out loud—do you hear how there’s a natural pause between the day of the month and the year? We don’t pause after the month, we pause after the day of the month. So correct comma usage would be: February 10, 1992.
If there’s a day of the week included, there’s a comma to separate that as well: Saturday, April 1, 2017.
If the date is listed in the middle of a sentence, there is a comma after the year as well: The concert scheduled for Tuesday, June 16, 1998, had to be rescheduled after the performer came down with bronchitis.
If the date is listed as day month year, then no commas are used: 23 October 2012.
Commas are used as place holders in numbers greater than 999. For example: 1,200 or 7,402,598,230,837. For numbers smaller than four digits, no comma is used (387 or 23). However, there are some exceptions. Do not use commas when writing out the year (2017), page numbers in a book or other long text, or in street addresses (1234 S. Main Street).
Commas are used to separate certification or degree from a person’s name when it is listed after their name. For example, Mrs. Susie Lu, Esq. or Dr. James Joyce, Ed.D.
It is not considered necessary to use commas for labels in a name like James Joyce Jr. or James Joyce Sr. even if it’s well down the generational line, like James Joyce IV.
When you directly address someone or something, the name or title should be set off by commas.
Thank you, Mr. Dansforth.
Members of the jury, thank you for your service.
And now, ladies and gentleman, I present to you Mr. and Mrs. Whitby!
This includes greetings in email or letters: Hi, Sam.
Commas are used to separate a series of words, phrases, or independent clauses when they are joined by conjunctions.
Brad studied English, Algebra, Chemistry, and French.
The candidate promised to lower taxes, rebuild the infrastructure, and cut the number of unemployed citizens.
Molly will bring the food, Marcus will set up the tables and chairs, Zach will put up the streamers, and Seamus will bring Mom and Dad to the party for the big surprise.
Please note: the Oxford comma or serial comma is the comma that comes right before the conjunction. Its use is stylistic; some institutions require it and some prefer you not use it. Please be sure to check with your instructor or institution about their preference. If in doubt and you have no authority to consult, it is usually expected in formal writing, so write items in a series with a comma before the conjunction, like this:
The strangest things we saw at the aquarium were the squid, octopus, and jellyfish.
Cows do not have feathers, wings, or claws.
If there is a list of adjectives or adverbs, commas are appropriate to separate independent modifiers of the noun; but if they don’t each modify the noun on their own, they do not get separated by commas. To determine if they are independent modifiers, see if you can switch their order without losing meaning. If you cannot, do not use a comma between them.
Sarah’s warm, fuzzy, dark blue sweater was her favorite to wear on cold days.
The swamp let off a fetid, damp smell in the early morning hours.
Mom’s bright blue bud vase was perfect for the bouquet of wildflowers. (There are no commas here because bright is actually modifying blue and not the bud vase. If you tried to change the order of the adjectives to Mom’s blue bright bud vase it wouldn’t make sense so we don’t interrupt the description with commas.)
When a word or phrase appears at the beginning of a sentence but is not actually part of the main clause of the sentence, it should generally be set off by a comma.
No, you shouldn’t have to go if you don’t want to.
Yes, I do expect him to finish the job before he leaves.
Well, it is probably okay this time.
In my opinion, that restaurant’s service was awful!
Pardon me, do you know how to get to the train station?
The same thing is true for words for phrases that appear at the end of a sentence but are not a part of the main clause.
I had a lovely time this evening, thank you.
Cassandra cannot attend practice on Thursday, however.
Pass the gravy, please.
Sometimes, sentences have extra parts that don’t need to be there to make the sentence complete or have it make sense. These nonessential parts are set off by commas to show that they are extraneous information. You should be able to take out what is in between the commas and still have a complete sentence.
I spoke to Margaret, the headmistress at John’s school, about the upcoming school science fair. (While the information included inside the commas helps to describe who Margaret is, that information is not necessary to understand the rest of the sentence, which would be left as “I spoke to Margaret about the upcoming school science fair.”)
Give the report to my assistant, Ms. Lee. (Assuming there is only one assistant, her name is nonessential. However, if this person has multiple assistants, then the comma would be omitted so the recipient would know which assistant she needs to find.)
The driver, knowing he was running late, honked his horn impatiently.
My best friend, Courtney, called me on my birthday.
Do not use commas to set off essential parts of a sentence (including clauses that begin with that) or between independent clauses. That creates what is called a comma splice and those are no good in writing.
Janet forgot her sunscreen, she got a bad sunburn. [These are two independent clauses and that little comma is not strong enough to hold them together. Either create two separate sentences (Janet forgot her sunscreen. She got a bad sunburn.), add a coordinating conjunction (Janet forgot her sunscreen, so she got a bad sunburn.), or join with a semicolon (Janet forgot her sunscreen; she got a bad sunburn.)]
The used car, that John bought, had only 12,000 miles on it. (If you take out the part of the sentence between the commas, this sentence makes no sense. That information is essential to understanding the sentence and cannot be omitted so there should not be any commas used in this sentence.)
Commas are used in sentences where there is a quotation. The comma pauses the reader or the speaker before the quoted material is presented and can introduce a quote or show an interruption in the quote.
“Yes,” Josephine replied, “I can go to the store.”
The epilogue to his book says, “All who work hard will receive great reward.”
First, let’s review types of clauses:
An independent clause is a group of words containing a subject and a verb, and it expresses a complete thought so that it can stand on its own as a complete sentence.
A dependent clause is a group of words that may contain a subject and a verb but does not express a complete thought and therefore cannot stand on its own as a complete sentence.
A simple sentence is one independent clause and no dependent clauses.
Sometimes, there is a conjunction in a simple sentence, so it can be tempting to include a comma when you see one of those. But generally there is no need for a comma in a simple sentence.
The pizza is hot and delicious.
Jorge reads and enjoys online blogs.
A compound sentence is two independent clauses joined by a coordinating conjunction (and, but, so, nor, for, yet, or), conjunctive adverb (therefore, however, nonetheless, etc.), or a semicolon (;). If there is a coordinating conjunction, there also needs to be a comma. Use a semicolon if the joining is by conjunctive adverb or semicolon.
Horatio plays piano, and Mike plays clarinet.
Horatio plays piano; however, Mike plays clarinet.
Horatio plays piano; Mike plays clarinet.
A complex sentence is one independent clause joined to one or more dependent clauses (in any order). The rule with complex sentences is that if the dependent clause comes before the independent clause, they are separated by a comma.
While this has been a lot of fun, I don’t think we’ll be doing it again.
Because the movie had sold out, James and Becca decided to go to the comedy club.
If the independent clause comes first, there is no need for a comma.
I don’t think we’ll be doing this again even though it was a lot of fun.
James and Becca decided to go to the comedy club because the movie had sold out.
If the dependent clause comes in the middle of the sentence, determine if it is essential (no commas) or nonessential (set it off with commas).
A compound-complex sentence is a sentence that includes two or more independent clauses and at least one dependent clause. In the case of a compound-complex sentence, if it starts with a dependent clause that refers to both independent clauses, set the dependent clause off with a comma but do not include a comma between the independent clauses.
If the dependent clause comes between the two independent clauses and applies only to the second one, then set the dependent clause off with commas.