Commas are punctuation marks used to separate words, phrases, and clauses for clarity and pacing. Specific grammar rules in different style guides determine where to place commas, and some rules vary by discipline. While this handout lists general concepts, always work with your audience and assignment in mind.

Between Independent Clauses Separated by a Conjunction

An independent clause is a group of words that can form a complete sentence on its own. Two independent clauses connected by a coordinating conjunction (for, and, nor, but, or, yet, so) must have a comma before the conjunction.

• Example: Sabaa woke up sick again, so I told her to sleep
• Example: I went to Mexico, and I visited Honduras and Belize afterward.

After an Introductory Dependent Clause

A dependent clause is a group of words that depend on an independent clause to form a complete sentence. They often begin with a subordinating conjunction (although, after, because, if, until, when, as, while, etc.). A comma will generally come before the subject if other content comes before the subject of the sentence.

• Example: Although blue is his favorite color, he is wearing red today
• Example: When I get home from work, I will eat dinner.

After Introductory Adverbs and Phrases

Commas are usually used after introductory 1) adverbs (often words that end in -ly); 2) participial phrases (phrases that begin with a verb ending in -ing or -ed); 3) infinitive phrases (when the word to precedes a verb); and 4) prepositional phrases (phrases that begin with a preposition and end with a noun).

• Example: Incidentally, I was not late this morning. (adverb)
• Example: Hoping for the best, the child asked for more dessert. (participial phrase)
• Example: To arrive on time, we must leave here by six. (infinitive phrase)
• Example: In the dark, you can see the stars more clearly. (prepositional phrase)

Around Nonessential Words and Phrases

Words, phrases, and clauses that can be removed from a sentence without changing its meaning are nonessential and are set off with commas. Appositives are words or phrases that rename a noun. Commas set off nonessential appositives, which provide nonessential information about a noun.

• Example: The quality of the material, however, was beyond question. (word)
• Example: Ms. Green is, in my opinion, very successful in sales. (phrase)
• Example: The award was given to Olivia, Maria’s daughter. (appositive)
• Example: Lacrosse, a sport played hundreds of years ago, is still popular. (appositive)

In contrast, commas do not set off essential words and phrases, which provide necessary information.

• Example: I have two sisters; my sister Jane is coming to visit. (no commas because there are two sisters, the word Jane is necessary for clarity.)
• Example: The committee reached a decision that was not popular. (The adjective clause that was notpopular is necessary to know which decision was reached.)

Around Nouns of Direct Address

Commas set off the name or names of individuals being addressed.

• Example: Tell us, Mr. Gutenberg, how you came up with this marvelous machine. (name)
• Example: Jamie and Luke, please clean your room. (names)

Between Three or More Items in a Series

Commas separate words and phrases in a list or series of three or more items. Some style guides or disciplines omit the comma before the coordinating conjunction (also called the Oxford comma).

• Example: Mr. Ng wanted us to bring apples, milk, and bread. (words)
• Example: Rehearsals are held before school, during lunch, and at night. (phrases)

Between Coordinating Adjectives

Commas separate coordinating adjectives, which are multiple words that modify the same noun. Their order can be reversed, and they can be separated by the word and instead of a comma.

• Example: His excited, eager manner impressed us. (comma; the adjectives work if reversed. His manner is eager and excited.)
• Example: Everyone loved our former math teacher. (no comma; the adjectives do not work if reversed.)

With Quotations

Commas are used to offset quotations in a sentence.

• Example: “Research,” she said, “has found that being outside has many health benefits.”

With Places and Dates

For places, a comma should separate the name of a city from its state, province, or country. If a city is listed with its state, province, or country, include a comma after the name of the state, province, or country as well. No comma is needed for only one place element.

• Example: They moved here from Salt Lake City, Utah, three months ago. (comma)
• Example: We traveled to Mali two years ago. (no comma)

For dates, a comma is needed between the date (August 18) and year (1980) and between the day of the week (Monday) and its date. If a day of the month (13), month (April), and year (1998) are listed together, a comma is needed after the year as well. No comma is needed for only one or two date elements. These comma rules use U.S. style; date formatting varies by country.

• Example: Their sister was born on Monday, August 18, 1980. (comma)
• Example: I visited Peru on April 13, 1998, and stayed for one week. (comma)
• Example: Will you visit us in January? (no comma)
• Example: In November 2002, we went on a tour of Europe. (no comma)