Commas
Addresses, Cities, States, and Nations
Use commas to separate street name, city, and state.
Mariah lives at 2601 Main Street, Memphis, Tennessee 37501.
Use a comma to set off cities, states, and countries.
The city of Joplin, Missouri, is the birthplace of poet Langston Hughes.
International singing superstar Edith Piaf was born in Paris, France, and raised in a brothel.
Compound Sentences
Use a comma before a coordinating conjunction (and, but, yet, so, for, or, nor) that joins two independent clauses in a compound sentence.
The engineer designed a new nanosensor to detect brain injuries, and he is applying for a patent.
The students said they benefited from classroom discussion, but many had poor attendance.
A comma is not needed before every coordinating conjunction. In the following example, the conjunction joins two verb phrases, not two independent clauses, so no comma is needed.
The ice storm of 2009 downed power lines and damaged many mature trees around campus.
Coordinate Adjectives
Use a comma between coordinate (equal) adjectives. To test for equal adjectives, insert the word and between the modifiers. If the insertion does not alter meaning or create awkwardness, the modifiers are equal and should be separated with a comma.
The Mississippi is a deeper, wider river than the Red.
Jay could not see that Daisy was a self-centered, egotistical socialite.
Dates
Use a comma to set off the year in a full date. Do not use a comma for month and year only.
Samuel Clemens, better known as Mark Twain, was born November 30, 1835, in Florida, Missouri.
Isaac’s dissertation defense is scheduled for Friday, March 11, 2016.
Twain predicted his passing would come in April 1910 with the return of Halley’s Comet.
Introductory Elements
Use a comma following a subordinate clause, participial phrase, infinitive phrase, prepositional phrase, or adverb that precedes the main clause in a sentence.
When Blake completed his honors thesis, Professor Davis helped him select a graduate program.
Arriving late for physiology, Ethan found the classroom door locked.
To improve her stamina, Caroline began swimming laps in the university pool.
In some instances, writers overlook the comma preceding an introductory phrase.
However, you can keep this handout nearby as a quick reference.
Items in a Series
Use a comma between each item in a series of three or more items. The final comma, required in most style formats is also known as the Oxford comma.
Politico, Gizmodo, and The Huffington Post are three popular blog sites.
John is working on the following issues: punctuating clauses, using parallelism, and citing sources.
Modifying Phrases & Clauses
Use commas to set off modifying phrases and clauses that do not add essential information, also known as nonrestrictive modifiers. Restrictive modifiers add essential information and do not take commas.
The students, who had a review session last Thursday, are taking the final exam this afternoon.
The students who are nominated for scholarships sit in the front row of the auditorium.
Restrictive or non-restrictive? Read your sentence without the modifier. If the essential meaning is preserved, it is nonrestrictive. If the sentence becomes unclear without the modifier, it is restrictive.
Parenthetical Expressions
Use a comma to set off transitional phrases and words, tag questions, and statements of contrast.
The debate last week, however, was so raucous that fights broke out.
The City Council meeting, on the other hand, was civilized and calm.
The faculty’s first responsibility is to the students, isn’t it?
Roxie treated JoBeth as her daughter, not as an employee.
Quotations
Use a comma to introduce or conclude a quotation (exceptions follow).
Dr. Johnson said, “Today we announce the interim department director.”
“Some Tennessee biology teachers were fearful of the Monkey Law,” wrote Keith.
Do not use a comma if the signal phrase ends with the word that. When the language introducing a quotation forms a complete sentence, use a colon, not a comma.
Mason Keller argues that “solar energy will soon replace our fossil fuel portfolio.”
Dr. Johnson urged all in attendance to embrace the new initiative: “We trust all members of our parent organization to help promote the department, the curriculum, and the leadership.”