Handout Topic: Commas

What is a comma?

The comma is a frequently utilized, and arguably the most useful, punctuation mark. Commas can be used in a variety of ways in a sentence, and the rules governing comma use are therefore complex. In general, commas are used to adjust the rhythm of a sentence, or to provide greater clarity to a sentence.

When are commas used?Grammar manuals differ in their approach to describing comma use. If you are unsure about a particular rule, please see the Writing Resource Centre for further guidance. The following is a (condensed) list of the six most important (and most common) rules governing comma use.

Rule #1: Use a comma before a coordinating conjunction that is connecting two independent clauses (n.b. an independent clause could stand apart as its own sentence).

e.g. Greg went home to study, but he decided to have a nap instead.
e.g. My parents both went to the punk rock concert, and they even managed to have a good time.

Rule #2: Use a comma between items in a series, including the last one.

e.g. The three workshops being offered this month are on punctuation, the stages of writing a paper, and scientific writing.
e.g. For breakfast I ate pancakes, eggs and bacon, and toast and jam.

Rule #3: Use a comma to separate introductory elements from independent clauses.

e.g. After returning from the store, Bill watched television.
e.g. In fact, he watched TV for thirteen straight hours.

Rule #4: Use a comma (or pair of commas) to set off nonrestrictive or parenthetical elements. (Both parenthetical and nonrestrictive elements are not essential to the overall meaning of the sentence.)

e.g. The chair, which is my father’s favourite, was found downstairs in the basement.

(The information that the chair is my father’s favourite is not essential to the meaning of the sentence, and commas can be used to set it off. Note: nonrestrictive elements are always introduced by which. Restrictive elements are introduced by that.)

e.g. The lawnmower that is in the garage is broken.

(In this case, that is introducing a restrictive element that is essential. Perhaps there is more than one lawnmower that makes this information necessary. In any event, commas are not required to set off this information as they are above).

e.g. Mount Saint Vincent, unlike Saint Mary’s, offers a Bachelor of Education degree. (parenthetical, or non-essential, information)

Rule #5: Use commas to separate coordinate adjectives. (Coordinate adjectives are two or more adjectives that are describing the same noun. Grammar books differ on whether a comma is necessary when only two coordinate adjectives are being used.)

e.g. The position will require dedicated, insightful, accurate work.
e.g. I couldn’t help finding the long, boring, repetitive orientation session sleep-inducing.

Rule #6: Use a comma for certain typographical information, like dates, addresses, and numbers.

e.g. Today’s date is January 31, 2006.
e.g. I live in Halifax, Nova Scotia.