Punctuation Rules: Commas

You may have heard it said, “put a comma where you take a breath in a sentence,” but this is an ineffective rule that can lead to more comma errors. Instead, follow the comma guidelines in this handout to separate introductory phrases, listed items, independent and dependent clauses, and parenthetical expressions.

Introductory Phrases

Use a comma after introductory phrases to indicate the main thought of the sentence is beginning.

• However, they needed a weekly team meeting to organize the project.
• In 2018, the school of business added new initiatives to support student work.

Listed Items

Use commas to separate three or more items that appear in a list. This includes a comma before the coordinating conjunction (e.g., “and”), which is called the Oxford comma.

• Toni Morrison employs imagery, metaphor, and symbolism to highlight racist ideals of beauty in the South.
• Effective business plans include a problem statement, a research summary, and recommendations for solutions.

Independent Clauses

Use a comma and a coordinating conjunction (for, and, nor, but, or, yet, so) to separate independent clauses.

Keep in mind that independent clauses can stand on their own as a complete thought and contain both a subject and a predicate.

• She led her high school club’s meetings, so she knew how to keep discussions on topic.
• Daniel Heath Justice argues that scholars should remain humble, and they should remember that the more they learn the less they know.

Dependent Clauses

Use a comma after dependent clauses that appear at the start of a sentence. *Keep in mind that dependent clauses cannot stand on their own as a complete thought because they rely on an independent clause to make sense

• If the project was going to get done on time, they needed to schedule a weekly team meeting.
• Because they had a tight deadline, they planned weekly team meetings to complete the project.

However, do not use a comma before a dependent clause that appears at the end of a sentence.

• They needed to schedule a weekly team meeting if the project was going to get done on time.
• They planned weekly team meetings to complete the project because they had a tight deadline.

Parenthetical Expressions

Put commas around expressions that can be removed from the sentence without changing the meaning of the sentence.

• Edgar Allen Poe’s work, which was dark and moody, captured the imagination of his readers.
• Some restaurants, especially those close to campus, are providing takeout this fall.
• The textbooks, however, were more expensive than I expected.

For more information about grammar, consult the following handout from Writing Services:

• Sentence Types

In addition, see Maxine Ruvinsky’s book, Practical Grammar: A Canadian Writer’s Resource.

Writing Services, Wilfrid Laurier University, CC By-NC 2023