commas
Writing Center
SMC Campus Center
621 W. Lombard St. Room 307
www.umaryland.edu/writing
410-706-7725
1
Version 3.0
Commas are tiny marks that can cause big problems. This handout will help you know when and how to use commas.
General Information
Most often, commas show readers how the words or phrases contained in a given sentence fit together.
They also help to signify a break in the action or, for example, when a reader should pause. In
addition, commas distinguish what information is absolutely necessary in a sentence.
The Oxford Comma
Also known as a serial comma, the Oxford comma is placed immediately before the conjuncon—usually “and,”
“or,” or “nor”—in a series of three or more terms.
Without the Oxford comma: Would you like steak, chicken or pork for dinner?
With the Oxford comma: Would you like steak, chicken, or pork for dinner?
While this might seem like a trivial disncon, the Oxford comma can eliminate confusion.
Confusing: I have invited my parents, Lloyd and Marilyn.
Note: Without the Oxford comma, it is not clear whether Lloyd and Marilyn are the parents or separate
invitees. In other words, it is not clear if there are four invitees or two.
Better: I have invited my parents, Lloyd, and Marilyn.
Note: The Oxford comma makes it clear that Lloyd and Marilyn are separate invitees.
The 6th edion of the APA Publication Manual requires the Oxford comma.
Combining Elements
When combining elements, the comma indicates where one element ends and another begins.
Note: For more information on clauses, please see our handout on this topic.
Combining Independent Clauses
To join two independent clauses, you must use a comma and a coordinating conjunction, such as “and,”
“but,” “or,” etc. Place the comma at the end of the first sentence, just before the conjunction.
Example: It’s terribly cold outside, but I think I’ll leave my jacket at home.
Version
Writing Center
SMC Campus Center
621 W. Lombard St. Room 307
www.umaryland.edu/writing
410-706-7725
2
Note: For more ways to combine independent clauses, please see our “Comma Splices” or “Run-ons”
handouts.
Combining Independent and Dependent Clauses
Subordinate clauses are dependent clauses which begin with a subordinating conjunction. If the
subordinate clause comes before your independent clause, use a comma at the end of the
subordinate.
Example: Because I have a big day tomorrow, I have to get plenty of rest
Note: “Because I have a big day tomorrow” is a subordinate clause.
However, when joining a subordinate clause to the end of an independent clause, do not use a comma
with the subordinating conjunction.
Example: I have to get plenty of rest because I have a big day tomorrow.
Note: “Because I have a big day tomorrow” is a subordinate clause.
Introductory Elements
When adding an introductory element to your sentence, use commas to help your readers distinguish the
introduction from the rest of the sentence.
Introductory clauses are subordinate clauses, which means they begin with a subordinating conjunction,
such as “if,” “since,” “when,” etc.
Clause: If I get up early enough, I will make it to your gym class.
Clause: Since she had already eaten, she did not order anything during lunch.
Note: For more information about subordinating conjunctions, please see our “Conjunctions” handout.
When a sentence begins with an introductory phrase of three or more words, insert a comma after the
phrase.
Phrase: After the party, she went home and fell asleep on her bed.
Phrase: The clear choice of the people, the candidate humbly accepted her nomination.
Note: For more information on phrases, please see our handout on this topic.
Some introductory words also require a comma. Usually, these words are conjunctive adverbs, like
“additionally,” “however,” and “therefore.”
Word: However, we must not ignore other possibilities.
Word: Therefore, she should act now.
Items in a List
When joining three or more items in a list, use commas to distinguish the words, phrases, or clauses in the
series. Be sure to use an Oxford comma before the conjunction.
Example: I need to purchase peaches, strawberries, tomatoes, and cucumbers at the farmers’ market.
Coordinate Adjectives
Coordinate adjectives are adjectives which describe the same noun. If the word “and” can be inserted
Writing Center
SMC Campus Center
621 W. Lombard St. Room 307
www.umaryland.edu/writing
410-706-7725
3
between two adjectives, or if the order of the adjectives can be reversed, they need to be
separated by a comma.
Example: Mrs. Elderberry is a kind, generous woman.
Note: You can tell that “kind” and “generous” are coordinate adjectives because you could very easily write
that Mrs. Elderberry is a “kind and generous woman” or a “generous and kind woman.”
You do not need to use commas with cumulative adjectives—adjectives that build on each other to modify
a noun. In other words, if the adjectives cannot be reordered, do not use commas.
Example: It is an ancient Mayan legend.
Note: You can tell that “ancient” and “Mayan” are cumulative adjectives because they build on each other.
“Mayan” modifies “legend,” and “ancient” modifies the resulting phrase “Mayan legend.”
Indicating Supplemental Information
When used in pairs, commas indicate information that is non-essential or supplemental. Think of the
commas as handles—you could use them to remove the clause from the sentence without aecting
its basic meaning.
Adjective (Relative) Clauses
Adjective clauses (also known as relative clauses) act as adjectives, meaning that they provide additional
information about nouns. These clauses usually begin with a relative pronoun (e.g., “who/whom,”
“that,” or “which”).
There are two types of adjective clauses: restrictive and nonrestrictive. Restrictive clauses provide
essential information about the nouns they modify and cannot be removed from the sentence
without altering its meaning. Non-restrictive clauses do not restrict the nouns they modify—they
add supplemental but nonessential information.
Do not use commas to set o restrictive adjective clauses.
Restrictive: The guests who were seated ate the pie.
Note: This sentences means that only the guests who were seated ate the pie. The sentence would not mean
the same thing if the restrictive clause “who were seated” were removed.
Use a pair of commas to set o non-restrictive adjective clauses.
Non-restrictive: The guests, who were seated, ate the pie.
Note: This sentence means that all of the guests ate the pie and that they happened to be seated. The
nonrestrictive clause could, in theory, be removed and the sentence still retain its meaning.
Note: For more information on adjective clauses, please see our “Clauses” and “Pronouns” handout.
Appositives
Apposition occurs when two nouns or noun phrases which refer to the same person, place, or thing are
placed side-by-side. Within this appositive pair, the second noun essentially explains or expands
the meaning of the first.
Example: This is my friend Dale.
Note: “My friend” and “Dale” are appositives.
Writing Center
SMC Campus Center
621 W. Lombard St. Room 307
www.umaryland.edu/writing
410-706-7725
4
Like adjective clauses, apposition can be either restricve or non-restricve. Use commas for non-
restrictive apposition. Do not use commas to set o restrictive apposition.
Restrictive: My brother Jon will meet you there.
Note: Since “Jon” restricts the phrase “my brother,” this sentence suggests that the speaker has multiple
brothers and that Jon is the specified one who will be meeting the listener.
Non-restrictive: My brother, Jon, will meet you there.
Note: Since “Jon” could in theory be removed, this sentence suggests that the speaker has only one brother.
Direct Address
When addressing someone directly, set that person’s name in commas.
Example: Let’s eat, Grandma, before our dinner gets cold.
Signaling Contrast
Tag Questions
Somemes statements end in brief quesons. When this happens, use a comma to separate the two parts of
the sentence.
Example: You’re not really going to punish me, are you?
Final Elements
Use a comma to highlight the contrast in short elements at the end of a sentence.
Example: The bike belongs to my brother, not you.
Introducing Quotations
Before Quotations
Use a comma to separate what is being said from who said it. If used before a quotaon, the comma should go
aer the last word before the quote begins.
Example: He said, “I think it’s time for us to go.”
After Quotations
If used at the end of a quotaon, the comma should go aer the last word of the quote but before the end
quotaon marks.
Example: “I’m not sure I’m ready to leave,” she retorted.
Interrupting Quotations
If a full sentence in a quotation is interrupted, one comma should be placed aer the last word in the rst
part of the quote, (i.e. inside the quotaon marks) and another aer the last word of the interrupng
material.
Example: “I don’t care if you’re ready,” he hissed, “or if you don’t want to for whatever reason!”
Writing Center
SMC Campus Center
621 W. Lombard St. Room 307
www.umaryland.edu/writing
410-706-7725
5
Other Quotation Mark Use
In all cases in which quotation marks are used but they are not setting o a direct quotation, the comma
goes inside the quotes.
Example: The test groups were termed “heavy users,” ”moderate users,” and “light users.”
My sister says she “surfs,” but she actually just boogie boards.
Note: For more information on how to use quotation marks, please see our handout on this topic.
Other Uses
Dates
Use a comma to separate the day of the month from the year and after the year.
Example: Karen graduated on June 5, 2003, from the University of Maryland.
If any part of the date is omied, leave out the comma.
Example: Karen graduated from the University of Maryland in June 2003.
Place Names
Use a comma to separate the city from the state and after the state in a document.
Example: I lived in Baltimore, Maryland, for 20 years.
If you use the two-letter capitalized form of a state in a document, you do not need a comma after the
state.
Example: I lived in Baltimore, MD for 20 years.
Titles & Degrees
Use commas to surround degrees or titles used with names. Commas are no longer required around Jr.
and Sr. Commas never set o I, II, III, etc.
Example: Silvia Franklin, M.D., knew Sam Jones Jr. and Charles Pointer III.
Common Errors
Comma Splices
A comma alone is insucient to join two independent clauses (i.e., simple sentences). When you join two
sentences with only a comma, you create a comma splice.
Comma Splice: It’s terribly cold outside, I think I’ll leave my jacket at home.
Correct: It’s terribly cold outside, so I think I’ll leave my jacket at home.
Note: For more information on commas splices, please see our handout on this topic.
Unnecessary Commas with Compound Subjects
Unless you have a list of three or more subjects, there’s no need to separate with commas.
Writing Center
SMC Campus Center
621 W. Lombard St. Room 307
www.umaryland.edu/writing
410-706-7725
6
Unnecessary Comma: Bill, and Tom went to the store.
Note: “Bill” and “Tom” are the subjects of the sentence. Since there are only two subjects, there is no need to
separate them with a comma.
Unnecessary Comma: Walking the dog, and buying groceries are my least favorite activities.
Note: “Walking the dog” and “buying groceries” are gerund phrases acting as the subjects of the sentence.
Since there are only two subjects, there is no need to separate them with a comma.
Necessary Comma: John, Paul, and George are my favorite Beatles
Note: “John,” “Paul,” and “George” are the subjects of the sentence. Since there are three subjects, commas
are necessary.
Unnecessary Commas with Compound Predicates
The predicate is the part of the sentence that contains the verb and says something about the subject.
Unless you have a list of three or more predicates, there’s no need to separate predicates with
commas.
People often make this error by thinking they are combining two independent clauses. Remember that,
when joining two independent clauses, each independent clause will have a separate subject and
predicate.
Unnecessary Comma: She went to the post oce, and mailed a letter.
Note: “Went to the post oce” and “mailed a letter” are both predicates connected to the subject “she.”
Since there are only two predicates, there is no need to separate them with a comma.
Unnecessary Comma: He runs on lakes and trails, and swims in rivers and lakes.
Note: “Runs on lakes and trails” and “swims in rivers and lakes” are both predicates connected to the subject
“he.” Since there are only two predicates, there is no need to separate them with a comma.
Necessary Comma: They paint houses, repair fences, and dig ditches.
Note: “Paint houses,” “repair fences,” and “dig ditches” are all predicates attached to the subject “they.” Since
there are three predicates, the commas are necessary.
Omitted Commas with Direct Address
Omitting commas when addressing someone directly can lead to unintentionally humorous sentences. In
fact, remembering these humorous mistakes can help you avoid this problem.
Without Commas (Cannibalism): Let’s eat Grandma!
With Commas (Respect for the Elderly): Let’s eat, Grandma!
References
Fogarty, M. (2008). Grammar girl’s quick and dirty tips for better writing. New York, NY: St. Martin’s Grin.
Straus, Jane. (2008). The blue book of grammar and punctuation: An easy-to-use guide with clear rules, real-world examples,
and reproducible quizzes. San Francisco, CA: Jossey-Bass.
Thurman, Susan. (2003). The only grammar book you’ll ever need: A one-stop source for every writing assignment. Avon, MA:
Adams Media.
Truss, L. (2003). Eats, shoots & leaves: The zero tolerance approach to punctuation. New York, NY: Gotham Books.
