Punctuation: Commas

The convict said the judge is mad.
The convict, said the judge, is mad.

A general rule of thumb – when a pause is needed in a sentence for the meaning to be clear, you probably need a comma. Many people rely on this rule of thumb entirely. However, the rule of thumb method does not always work. This handout shows the rules around comma use.

The 6 Rules For Using Commas 

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1. Commas separate introductory parts of sentences from the main sentence.

A comma is used after introductory words, phrases or clauses. Another way to look at it is that commas come before the main subject of a sentence. In this way, the comma is a sign to the reader that the main subject is coming.

Words: Unfortunately, our picnic was rained out.
Phrases: Laughing to himself, he drew a cartoon.
At 6:00, the family sat down to dinner.  
In conclusion, the law needs to be changed.
Clauses: After she finished her paper, she fell into bed and slept.
If I won the lottery, I would travel.
Because we had never met, we felt awkward at first.

2. Commas separate items in a list of 3 or more items. (optional commas before the coordinator/item)

She invited Amanda, Amy, Nick and Claire to her party.
Strawberries, watermelon and apricots are my favorite fruits.
A student has to go to class, take notes, read textbooks and write exams.
The shift changes at midnight, eight in the morning and four in the afternoon.

Note
: In these lists, a comma has not been used before the and. However, some people prefer to use commas before the and.

For example:

She invited Amanda, Amy, Nick, and Claire to her party.
Although either with or without the comma is acceptable, it is good to be consistent.

3. Commas are used with coordinators (and, so, but, for, yet, or, nor) to separate two complete ideas.

A comma is used before a coordinator which joins two independent clauses. An independent clause expresses a complete thought, like a simple sentence. The only coordinators are for, and, nor, but, or, yet, and so.

A good way to remember these coordinators is to remember the phrase FAN BOYS.

For They went to a fancy restaurant, for it was his birthday.
And He ordered salmon, and she ordered pasta.
Nor He didn’t have soup, nor did he order anything to drink.
But She wanted to have oysters, but the restaurant had run out of them.
Or Would you like dessert, or would you prefer to get your bill?
Yet They loved the chocolate cake, yet the pieces were too big to finish.
So The service was excellent, so they left a big tip.

Note: The comma is optional when both independent clauses are short.

Remember that commas are used only when the coordinator joins two separate subject/verb combinations. If a sentence has one subject with two verbs, you should not use a comma.

For example, She sat down and ordered a coffee.

This does not need a comma as there is only one subject.

Similarly, if the sentence has two subjects but only one verb, no comma is used.

For example, The angry woman and her crying children left the store without any groceries.

4. Commas separate words that interrupt the flow of a sentence.

When information is added to a sentence and that information interrupts the flow of ideas of the sentence, commas are used to separate the interruption from the rest of the sentence.

Here are some examples:

Julie Payette, for example, is an excellent role model for girls.
Marc Garneau, on the other hand, is famous because he was Canada’s first astronaut.
John A. McDonald, Canada’s first Prime Minister, had a drinking problem.
Justice Institute of British Columbia is in New Westminster, B.C.’s first capital.
A salmon, its sides gleaming, struggled up the river.
Nick, who struggled with grades in high school, is doing quite well in college.
Many downtown eastside residents use the Carnegie Centre, which sits at Hastings and Main.

To decide whether something is an interrupter, you should try taking those words out of the sentence. If you can take them out and the meaning of the sentence is still clear, you have an interrupter. However, if you take the words out and the meaning is no longer clear, there is no interrupter, and you don’t need commas.

For example:

Sir Wilfred Laurier, who was a past prime minister of Canada, is pictured on our five dollar bill.

Notice that if you take out who was a past prime minister of Canada, the meaning of the main sentence is still clear. Who was a past prime minister of Canada is extra information, not essential to understanding the main sentence. Even without it, we know whose picture is on the five dollar bill.

However, look at this sentence:
The man who lives down the street got arrested.

Notice if you take who lives down the street out of this sentence, you don’t know anymore who was arrested. Who lives down the street is needed to identify the man. For this reason, who lives down the street is essential information, and no commas are used.

5. Commas separate a direct quotation from the rest of a sentence.

Commas separate direct quotes from your own writing.

She said, “Pasteur really made a difference.”
Expect snow overnight,” predicted the TV weather reporter.
Hockey,” explained Sam, “is my favorite winter sport.”

Commas are used when you directly quote a complete idea. When only a word or phrase is quoted, you don’t need commas.

She described the television as an “idiot box”.

Commas are also not used when you report what someone said using indirect speech.

Sam explained that hockey was his favorite winter sport.

6. Commas separate components of dates, numbers and addresses.

Time: September, 1980
January 1, 2000
Monday, June 14, 1999
4:30, December 31
6:42 a.m., July 27, 1985
Numbers: 1, 364
23,900,000

Note that commas with numbers have become optional in science and mathematics.

Place: Paris, France
Moose Jaw, Saskatchewan
3652 Main Street, Vancouver
700 Royal Ave., New Westminster, BC, V3L 5B2, Canada


Proofreading For Commas

The most straightforward way to proofread for commas is to read your writing out loud. When you need to pause slightly to make the writing make sense, you probably need a comma. However, be cautious because over-use of commas is a more common problem than under-use. Whenever you are in doubt about whether a comma is needed, refer back to the rules in this handout to help you make your decision.  Remember that when you have a list of two items in a list, there is not a comma befor the second item.

Adapted from Douglas College’s Commas without exercises

For Further Practice

Eats, shoots & leaves: the zero tolerance approach to punctuation by Lynne Truss. Available at JIBC Library.

Last updated December 17, 2015