Comma Rules
Contrary to popular belief, commas don't just signify pauses in a sentence.
In fact, precise rules govern when to use this punctuation mark. When followed, they lay the groundwork for clear written communication.
1. Use a comma before any coordinating conjunction (For, And, Nor, But, Or, Yet, So – FANBOYS).
· Example: "I went running, and I saw a dog."
An independent clause (or main clause) is a unit of grammatical organization that includes both a subject and verb and can stand on its own as a sentence.
In the previous example, "I went running" and "I saw a dog" are both independent clauses, and "and" is the coordinating conjunction that connects them. Consequently, we insert a comma.
If we were to eliminate the second "I" from that example, the second clause would lack a subject, making it not a clause at all. In that case, it would no longer need a comma: "I went running and saw a dog."
2. Use a comma after a dependent clause that starts a sentence.
· Example: "When I went running, I saw a dog."
A dependent clause is a grammatical unit that contains both subject and verb but cannot stand on its own, like "When I went running ..."
Commas always follow these clauses at the start of a sentence. If a dependent clause ends the sentence, however, it no longer requires a comma.
Only use a comma to separate a dependent clause at the end of a sentence for added emphasis, usually when negation occurs.
3. Use commas to offset appositives from the rest of the sentence.
Appositives act as synonyms for a juxtaposed word or phrase.
· Example: "While running, I saw a golden retriever, a kind of dog."
"A kind of dog" is the appositive, which gives more information about "a golden retriever."
If the appositive occurs in the middle of the sentence, both sides of the phrase need a comma. As in, "A golden retriever, a kind of dog, ran up to me."
Don't let the length of an appositive scare you. As long as the phrase somehow gives more information about its predecessor, you usually need a comma.
· "A golden retriever, the kind of dog I saw when I went running, ran up me."
There's one exception to this rule. Don't offset a phrase that gives necessary information to the sentence. Usually, commas surround a non-essential clause or phrase.
For example, "The dog that ran up to me scared my friend" doesn't require any commas. Even though the phrase "that ran up to me me" describes "the dog," it provides essential information to the sentence. Otherwise, no one would know why the dog scared your friend. Clauses that begin with "that" are usually essential to the sentence and do not require commas.
4. Use commas to separate items in a series.
· Example: "I saw a dog, a magician, and a parade when I went running."
That last comma, which is known as the serial comma or Oxford comma, causes serious controversy. Although many consider it unnecessary, others insist on its use to reduce ambiguity or uncertainty.
Ms. Cross recommends using the Oxford comma to avoid confusion.
5. Use a comma after introductory adverbs.
· "Finally, I went running."
· "Unsurprisingly, I saw a dog when I went running."
Many adverbs end in "ly" and answer the question "how?" How did someone do something? How did something happen? Adverbs that don't end in "ly," such as "when" or "while," usually introduce a dependent clause (refer back to rule #2).
Also insert a comma when "however" starts a sentence, too. Phrases like "on the other hand" and "furthermore" also fall into this category.
Many careful writers, however, discourage starting a sentence with “however”. A better method would be to use "however" within a sentence after the phrase you want to negate, as in the previous sentence.
6. Use a comma when attributing quotes.
The rule for where the comma goes, however, depends on where attribution comes.
If attribution comes before the quote, place the comma outside the quotations marks.
· The runner said, "I saw a dog."
If attribution comes after the quote, put the comma inside the quotation marks.
· "I saw a dog," said the runner.
7. Use a comma to separate each element in an address. Also use a comma after a city-province combination within a sentence.
· "I go to school at 2145 Jones Avenue, North Vancouver, BC.”
· "Vancouver, BC, is a great city."
8. Also use a comma to separate the elements in a full date (weekday, month and day, and year). Also separate a combination of those elements from the rest of the sentence with commas.
· "March 15, 2013, was a strange day." Even if you add a weekday, keep the comma after "2013."
· "Friday, March 15, 2013, was a strange day."
· "Friday, March 15, was a strange day."
You don't need to add a comma when the sentence mentions only the month and year. For example, "March 2013 was a strange month."
9. Use a comma when the first word of the sentence is freestanding "yes" or "no."
· "Yes, I saw a dog when I went running."
· "No, the dog didn't bite me."
10. Use a comma when directly addressing someone or something in a sentence.
My students often ask, "Ms. Cross, have you marked our quizzes?"
This clever meme shows the problem with incorrect placement of this comma. "Stop clubbing baby seals” reads like an order to stop harming infant mammals of the seal variety.
The version with a comma, however, instructs them to stop attending hip dance clubs. "Stop clubbing, baby seals." You can dance if you want to, baby seals.
11. Use a comma between two adjectives that modify the same noun.
· Example: "I saw the nice, friendly dog when I went running."
Only coordinate adjectives require a comma between them.
Two adjectives are coordinate if you can answer yes to both of these questions:
a. Does the sentence still make sense if you reverse the order of the words?
b. Does the sentence still make sense if you insert "and" between the words?
Since "I saw the friendly, nice dog " and "I saw the nice and friendly dog" both sound fine, you need the comma.
Sentences with non-coordinate adjectives, however, don't require a comma.
· Example, "I lay under the powerful summer sun."
"Powerful" describes "summer sun" as a whole phrase. This often occurs with adjunct nouns, a phrase where a noun acts as an adjective describing another noun — like "chicken soup" or "dance club."
12. Use a comma to offset negation in a sentence.
· Example: "I saw a dog, not a cat, when I went running."
In this case, you still need the comma if the negation occurs at the end of the sentence. "I saw a dog, not a cat."
Also use commas when any distinct shift occurs in the sentence or thought process. For example, "The cloud looked like an animal, perhaps a baby seal."
13. Use commas before every sequence of three numbers when writing a number larger than 999. Two exceptions to this rule are writing years and house numbers.
· Examples: 10,000 or 1,304,687.