Commas

Commas are mostly used to ensure clarity and give emphasis.

Three or More Items in a List

Separate items in a list when the list has at least three items. The last comma before the conjunction (“and” or "or") is optional and often preferred for clarity. This comma is called an Oxford Comma or Serial Comma and can be used to equally emphasize each item in the list.

Example, with Oxford Comma: This effort is called the Common Core State Standards Initiative (CCSSI), and its College- and Career-Readiness Standards for English would include demonstrating a command of grammar, usage, and mechanics in Standard Written English (CCSSI, 2010).

Example, without Oxford Comma: This effort is called the Common Core State Standards Initiative (CCSSI), and its College- and Career-Readiness Standards for English would include demonstrating a command of grammar, usage and mechanics in Standard Written English (CCSSI, 2010).

Use the Oxford Comma when needed to prevent issues with clarity.

Example: For breakfast, I ordered scrambled eggs, toast and butter, coffee, and water.

The comma after "coffee" clarifies that coffee and water are two separate items and not a unit like "toast and butter."

Introductory Words, Phrases, and Clauses

Commas can follow words and phrases that begin a sentence. This comma is optional but can be used to clearly distinguish where the introductory element ends and the main sentence begins.

Example: Hopefully, poverty will one day cease.

Example: Within this conversation, all of the authors agree that the topic of first-year composition is worth discussing and that a first-year composition course cannot and should not prepare students to write across the university.

Example: On the contrary, VHS tapes have been non-existent in stores for quite some time.

Commas must follow introductory clauses, which have their own subject and verb.

Example: Even though Ruth moves out, she is only able to raise her children in the same kind of environment, with the poverty that shapes each character in the novel.

Example: Because the show was already sold out, everyone must have bought tickets the very first day.

Proofreading Tip

Introductory words, phrases, and clauses can be completely removed, and the sentence will still make sense. When you find an introductory element, find where it ends and follow it with a comma.

Example: After we had the big snow storm salt was needed on the icy roads.

After we had the big snow storm, salt was needed on the icy roads.

Multiple Adjectives

Commas separate two or more adjectives before a noun, if at least one of the following situations is true:

  • the order of the adjectives can be reversed

AND/OR

  • the adjectives could be separated by the conjunction "and"

Example: Edna marries not for love but for childish, selfish reasons.

Comma is used because these adjectives pass both tests: they can be reversed (selfish, childish reasons), and they can be combined by "and" (childish and selfish reasons).

Example: Jesse picked the blue bouncy ball from the basket.

Comma is not used because these adjectives fail both tests: they cannot be reversed without sounding "off" (bouncy blue ball), and they cannot be combined by "and" (blue and bouncy ball).

Conjunctive Adverbs (Transition Words)

Conjunctive adverbs help you transition between ideas and complete sentences. Here are some examples:

  • therefore
  • however
  • furthermore
  • thus
  • rather
  • moreover
  • nonetheless
  • likewise
  • similarly
  • accordingly
  • unfortunately
  • consequently
  • additionally
  • still

Use commas to set off transition words from the sentence, no matter their location.

Example: The process should still be prompt, however, and the departments should complete their investigations within 30 business days.

Example: Unfortunately, some of Casa Loma's interior was left unfinished after Sir Henry Pellatt went bankrupt.

Commas should follow transition words that combine two sentences. A semicolon should be placed before the transition word.

Example: The reliability of the survey may be questionable; however, the research is valid.

Non-Essential Descriptions

Commas set off extra words, phrases, or clauses that are not necessary to understand the sentence.

Example: The Titanic's Grand Staircase, whose architecture has been brought to life in several museums, no longer exists on the ocean floor.

Example: Slinky, Woody’s most loyal friend, believed in him when the other toys didn’t.

Example: I have only one brother. My brother, who is in Iraq, will be coming home soon.

Don't use commas around descriptive information that is necessary to understand exactly whom or what you are talking about.

Example: I have two older brothers in the military: my brother who is in Iraq will be coming home soon.

"Which" vs "That"

"Which" clauses provide additional, unimportant information and need to be preceded by a comma.

Example: Tourists have never been allowed on the second floor of Graceland Mansion, which was opened in 1982.

This "which" clause provides an extra explanation of when Graceland Mansion was opened, but it is not necessary to understand the main point of the sentence.

"That" clauses, on the other hand, introduce sentences that are necessary to the meaning of the sentence and would not be preceded with a comma.

Example: The Model T was created for Henry Ford’s dream that high-quality, low-priced cars would be available to the general public.

This "that" clause describes Henry Ford's dream, which is the main point of the sentence and is necessary to understand the sentence.

Proofreading Tip

Use Microsoft Word's Find feature to locate "which" and "that" in your paper.

  • When "which" is followed by a verb, make sure "which" is preceded by a comma.
  • When "that" is followed by a verb, make sure "that" is not preceded by a comma.

Two or More Complete Sentences

Place a comma before the conjunctions "and," "but," "or," "for," or "yet" when they combine two complete sentences.

Example: Reed and Kellogg published their invention in several books, and their system was easier to understand than the balloon diagram previously in use.

Emphasis and Pauses

Commas can appear around phrases and clauses to slow your reader for emphasis. Commas can provide a little emphasis, while dashes provide more emphasis and parentheses de-emphasize information. 

Example: Daniel, in all fairness, had no choice but to become Mrs. Doubtfire.

Example: Kevin was able to fend off two burglars, even though he was home alone.

Locations and Dates

Commas separate the city from the state. A comma also follows the city and state when they appear together within a sentence.

Example: Oxford, Ohio, is home to Miami University.

Example: Oxford is home to Miami University.

Example: Ohio is home to Miami University.

Commas appear in the following places when listing out dates.

Example, with month first: Friday, December 25, 1988

Example, with day first: 25 December 1988

Commas follow a full date used within a sentence.

Example: September 11, 2001, marks the worst terrorist attack in U.S. history.

But don't use commas when writing just the month and year.

Example: September 2001 marks the worst terrorist attack in U.S. history.