Definition: a punctuation mark (,) indicating a pause between parts of a sentence. It is also used to separate items in a list and to mark the place of thousands in a large numeral.
Note: Do not rely on grammar or spelling checkers to identify missing or misused punctuation. Although a checker may flag possibly missing or incorrect marks, it cannot do much else. While I still recommend using these AI checkers while you’re writing, I insist that you also trust a qualified human being to copyedit any work that you are working toward publishing.
Commas are one of the most, if not the most, commonly used punctuation within sentences and know that they often indicate a pause. While there are occasions when a comma is required, sometimes you just have to use your judgement; if you would pause in speaking, use a comma in writing.
In Compound Sentences:
One main use for a comma is to separate two main clauses in compound sentences, paired with the conjugations and, but, or, nor, for, so, and yet.
- e.g. Carl selected one roll of wrapping paper, and Beth selected two.
- e.g. The weather was nice, but no one was at the park.
Note: Be careful not to confuse a compound predicate with a compound sentence. A compound sentence has two main clauses, meaning two distinct sentences.
- e.g. Carl selected one roll of wrapping paper and paid with debit.
In this compound predicate, there is only one subject (Carl), who is performing two actions (selecting wrapping paper and paying for it). The part “and paid with debit” doesn’t have its own subject and therefore cannot stand alone as a sentence.
You may omit the comma if the clauses that make up the compound sentence are closely related, if both clauses are short, or if the second relies on the first for its sense. However, if the sentence sounds better with a comma (if there is a natural pause) add it in.
- e.g. I want to go but I can’t.
- e.g. I write and she draws.
After Introductory Phrases and Clauses:
Introductory adverbial clause
- e.g. When it snows, the children play outside.
Introductory infinitive phrase
- e.g. To build a snowman, roll two large snowballs and stack them.
Long introductory phrase
- e.g. Four months after the end of the flu season in 2022, Stacy still aggressively sanitizes her hands everywhere she goes.
Note: How long is long? If you would pause after the phrase, use a comma.
Short introductory phrase (if confusion could exist without the comma)
- e.g. In 2022, 4,680 people died of Covid-19 in British Columbia, Canada.
- e.g. In Canada, geese are far more common than bears.
Note: Do not use a comma after an introductory phrase in an inverted sentence (one where the subject follows the verb).
- e.g. On the sidewalk of Pine Street sat a little boy with his bicycle.
NOT On the sidewalk of Pine Street, sat a little boy with his bicycle.
Before Adverbial Clauses:
Do not use a comma if the adverbial clause follows the main clause.
- e.g. The children play outside when it snows.
If the adverbial clause following the main clause is introduced by whereas, although, or because (subordinating conjunctions), use a comma only if one seems necessary.
- e.g. Maxine drove to the store to buy groceries because her mother asked her to.
Since a strong relationship appears between the two clauses, no pause occurs, and therefore no comma is needed. Sometimes, however, a comma is needed for sense; without a comma (without a pause), the sentence says something other than what the author means.
- e.g. Don’t worry about the wolves, because they live further north.
As opposed to:
- e.g. Don’t worry about the wolves because they live further north.
One sentence (with the comma) tells you not to worry about wolves, with the reason being that they live further north, and the other sentence (without the comma) tells you to worry about the wolves for reasons other than the fact that they live further north.
When using the word because, you must ask yourself each time whether there needs to be a pause. Usually, if the clause that introduces because is positive, you don’t need a comma.
- e.g. I bought tickets to the cinema because I love watching movies.
- e.g. Harold couldn’t go on the next ski trip, because he had to sell his skis.
To Set Off Transitional and Special Elements:
Use a comma after any parenthetical element that serves to break up the continuity. Within the sentence, use commas on both sides of the element.
- e.g. Oh, how wrong I was.
- e.g. However, we were unable to find the receipt to return the item.
- e.g. John, in fact, had two ways to get up the mountain.
- e.g. Vicki asked, amid the chaos, how to best discipline her children.
A comma may be omitted if there is no break in continuity.
- e.g. Greg finished Hal’s homework in addition to his own.
- e.g. Dave was able to afford a new house and furthermore able to afford a new car.
There must be a comma after however except as an adverb (“however hard I tried, I couldn’t beat Jan at baseball”).
Use a comma to set off etc.; yes or no at the beginning of a sentence; and the conversational well, now, or why.
- e.g. I asked the kids, aunts, uncles, grandparents, etc., what they wanted for Christmas, but forgot to ask my wife.
- e.g. Yes, Matt is the best in the business.
- e.g. Now, what do you think of that?
- e.g. Please, Arlene, think of the children.
- e.g. Goodbye, Chelsey.
Titles or degrees
- e.g. Linda Garvey, M.D.
In a Series:
Use commas to separate all elements in a series.
- e.g. Nancy packed swimwear, towels, and sunscreen for her trip to the beach.
Note: The comma before the and is called the series comma, or Oxford comma. Textbook publishers almost always use a series comma, magazine publishers almost never. The absence is also British style. Trade book publishers typically follow the author’s preference.
- e.g. Sally visited Germany, France, and Switzerland on her trip. [style with the series comma]
- e.g. He waited two hours, stood up in a rage and sprinted out of the room. [style without the series comma]
Use a comma between coordinate adjectives if the word and logically could be read between them.
- e.g. The crowd was filled with young, beautiful people. [young and beautiful]
Do not use a comma to separate an adjective from a word group.
- e.g. Alice walked up the wobbly wooden stairs. [not wobbly and wooden; “wooden stairs” is a word group]
- e.g. Ellie joined the others at the popular cop bar. [not popular and cop; “cop bar” is a word group]
Do not use a comma to separate an adjective from the noun it modifies.
- e.g. The gym attracted hardworking, committed people. [not hardworking, committed, people]
With Antithetical Elements:
An antithetical element contradicts the rest of the sentence or presents two parallel structures.
Do not use commas to set off elements in the not to…but to construction.
- e.g. We come not to stay cooped up but to explore on vacation.
- e.g. I went to Vegas not so much to gamble as to enjoy the lights.
Use commas to set off antithetical elements.
- e.g. Beth, not Georgia, was arrested for tax fraud.
Use commas to separate interdependent elements.
- e.g. The more carefully you listen, the better your understanding of the world will be.
- e.g. The darker the shadows, the brighter the light.
Note: A verb is not essential, but one can be used like in the first example. I did so because the two clauses are not technically parallel; the subject of the first clause is you, and the subject of the second clause is understanding. Whether the verb is used or not is personal preference.
Do not use commas in short interdependent phrases.
- e.g. The sooner the better.
Restrictive Verses Non-restrictive Elements:
First, a quick recap about what restrictive and non-restrictive elements are. A restrictive element cannot be removed from a sentence, as it is necessary for the sentence to make sense. In times when identification is necessary, it will tell you “which one.”
- e.g. The children who ran the race are tired.
This specifies that only the children who ran the race (not all children present or all children in the world) are tired. The sentence answers the question Which ones? and is restricted to only those children.
A non-restrictive element can be taken out of the sentence without changing the meaning. Such an element is surrounded by commas.
- e.g. My daughter, who is in high school, is on the honour roll.
What happens if that element is removed from the sentence?
- e.g. My daughter is on the honour roll. [my only daughter is on the honour roll]
The added text does not answer any question of Which Ones? As the person in question must only have one daughter. If the one speaking has more than one daughter, the added information who is in high school becomes a restricted element (note: only if the other daughter[s] is/are not also in high school).
- e.g. Only the people who aren’t driving are allowed to drink.
Test each sentence to see if it’s restricted to only those or only that; you’ll be able to tell right away whether the sentence is restricted.
With Non-restrictive Elements:
Use commas around non-restrictive elements.
- e.g. The spider caught a fly, which became tangled in the web.
- e.g. The spider, which caught a fly, feasted on its prey.
- e.g. Delilah Perkins, the most popular girl at the school, was unsurprised to be chosen for Prom Queen.
Do not use commas with restrictive clauses. In restrictive clauses, use that instead of which.
- e.g. The children that were in Ms. Hansom’s class were learning about geography. [only those children – not others]
There are some special cases of non-restrictive elements – elements that serve to clarify but are not needed. They are called parenthetical elements.
With Parenthetical Elements:
Use commas around parenthetical elements.
- e.g. Christmastime, Emma said, is a time for family to come together.
- e.g. They purchased pop, chips, candy, and so on, for the party.
Use commas before and after each element after the first in addresses and dates.
- e.g. On December 28, 1895, in Paris, France, the world’s first movie theatre was opened.
Use a comma after the first name of an inverted bibliographic reference.
- e.g. Johnson, Mary, and Franklin Welsh. The Psychological Effects of Living in a Cupboard. San Francisco: Nonexistent Press, 1980. [the first name, Mary Johnson, is inverted, whereas the second name is not; note that this book doesn’t actually exist]
An appositive is a word or group of words that renames the noun or pronoun that follows. There is no verb between a noun and its appositive.
Use commas around non-restrictive appositives.
- e.g. A great supporter of LGBT youth, Kristopher Dunn was appalled by the way Mr. Smith treated his child.
Do not use commas with restrictive appositives.
- e.g. My sister Sally is a writer. [my sister Sue is a doctor; alleges that the speaker has more than one sister]
- e.g. The playwright Shakespeare was a remarkable man. [there are other playwrights].
With Other Punctuation:
Use a comma to introduce or follow a direct quotation.
- e.g. Greg shouted, “Shoo!”
- e.g. “I need to sit down,” Marcus mumbled.
Not everything within quotation marks is a quotation. Do not use a comma to set off material within quotation marks used as a subject, object, or appositive.
- e.g. Olivia calls Harry “Golden Boy” around our friends.
- e.g. “Mayday” is the distress call for planes and ships.
A comma goes inside the end quotation mark of a direct quotation.
- e.g. “I’ll be back,” Arnold threatened.
A comma goes outside a single quotation only if the mark is used to indicate special usage, not if it is used in a quotation.
- e.g. The concept of ‘being’, which we discussed earlier, is difficult to understand.
Note: This is a philosophical usage only. Terms may be enclosed within double quotation marks or single quotation marks, and then the comma goes inside.
- e.g. The “tiny spear,” Bonny quickly found out, was in fact a screwdriver.
- e.g. For the entire trip back from visiting ‘Annoying Arnold,’ Felicia complained about every little thing.
Do not use a comma with an exclamation point or question mark.
- e.g. “Go away!” Jenny shouted at the figure following her.
- e.g. “Where are we going?” Frank asked as he climbed into the car.
A comma never precedes an open parenthesis (except typographically).
- e.g. According to Sarah (who never listened in science class), rainbows are created by leprechauns.
Depending on the style, a comma may be used in dialogue when a sentence trails off in dialogue.
e.g. “If Martha goes out into the woods…,” Max said. / “She may never come back. I know.”
For further information, see my other Punctuation articles:
Aaron, J.E. & Morrison, A. The Little, Brown Compact Handbook, 5th Canadian ed. Pearson, 2013, chap 5
Judd, K. Copyediting, A Practical Guide, 3rd ed. California, CA: Crisp Learning, 2001, chap 4