The CommaScribendi.com's editors explain what a comma is and highlight some common comma rules

A comma is the most important punctuation mark for ensuring clarity in a sentence. However, it is often incorrectly used, which can sometimes have comical results.

Using commas correctly ensures that the reader understands the meaning the author intends to convey. There are a few strict comma rules concerning usage, but many of the conventions are merely typical practices.

Exceptions exist, so authors should make the best decisions possible in the interest of clarity. Nonetheless, here are the most common comma rules:

Comma Rule #1: Separating items in a series with a comma

Three or more items (single words or phrases) in a series should be separated by commas, including the final item, which comes after the conjunction (almost always and or or). This final comma is known as a serial comma.

Consider the following example of a comma series:

I must remember to buy flour, eggs, milk, and chocolate if I'm going to bake that cake.

Comma Rule #2: Joining independent clauses with a comma

An independent clause is a group of words that can stand alone as a sentence. Two examples of an independent clause are:

We would all love to see the movie. I think we can still make it on time if we hurry.

When two independent clauses are joined by a coordinating conjunction (and, but, or, nor, for, so, and

yet), a comma precedes the coordinating conjunction.conjunction.

We would all love to see the movie, and I think we can still make it on time if we hurry.

However, when both independent clauses are short and there is no danger of misreading the sentence, the comma can be omitted.

The meeting ended and I went to the park.

Comma Rule #3: Joining dependent clauses with a

comma

A dependent clause is exactly what it sounds like: a group of words that depends on another clause to form a complete sentence. When a dependent clause follows an independent clause to make one sentence, no comma is needed.

We shuffled into the dark theater and noticed the previews were just ending.

However, some sentences begin with a dependent clause. A comma is needed following this clause, as is shown in the following example.

If you don't want to play the recorder, please raise your hand.

Comma Rule #4: Using a comma following an introductory

word group

Some sentences open with a group of words that explain when, where, why, or how the main action of the sentence occurs. A comma follows this introductory word group and explains to the reader that the main part of the sentence is about to begin. Here's a good example:

On the edge of the stream, a male frog croaked out his mating song.

Some sentences begin with a phrase describing the nounor pronoun that immediately follows. A comma follows this introductory phrase.

Knowing he was allergic to melon, Paul did not eat the fruit salad.

Some sentences begin by directly addressing someone. A comma follows the name.

Elise, I love your dress!

Some sentences begin (or end) with words that answer or ask a question. A comma follows this word or phrase if it is at the beginning of the sentence and precedes it if the phrase is at the end.

Yes, he is going to the play.

That dog behaved well, didn't he?

Some sentences begin with mild interjections, which should be followed by a comma.

My, he is tall.

Comma Rule #5:Inserting interrupters

Phrases that interrupt the sentence to provide information that is not necessary to the main idea of the sentence (also known as non-restrictive phrases) are set apart with commas.

Here are a few examples:

The band, which won several awards last year, played at the stadium all night long.

The garden, with its tall wooden fence and muddy pathways, produced a large crop of tomatoes.

The current manager, it seems, was not the best one for the job.

Comma Rule #6: Using commas in direct

quotations

Expressions preceding or following direct quotations are set apart by commas.

"I will have a glass of red wine," she told the waiter.

"A rose by any other name would smell as sweet," William Shakespeare wrote.

For such an inconspicuous little mark, the comma performs a wide variety of functions in a sentence. If you are still unsure about commas, consider taking our top-notch online grammar course, GrammarCamp.com.

Using Commas

Commas remove ambiguity and ensure that readers understand the meaning the author wants to convey. Let's continue looking at some additional grammatical constructions that call for comma usage.

A comma separates the month and date from the year.

On March 23, 2009, David and Alice will be married.

However, if the date is written in the inverted style, or if only the month and year are given, no comma is needed.

The new law goes into effect 30 May 2010.October 2006 was the month we went over our budget.

Using Commas: Dates

A street address, city, and state or province are separated by commas.

I am moving to 45 Magnolia Lane, Toronto, Ontario.

Using Commas: Addresses

In numbers longer than four digits, commas separate the numbers into groups of three, starting from the right side.

15,000

10,000,000

This convention is predominantly found in North American and British English. Numbers may be punctuated differently in other languages.

Using Commas: Numbers

If a title follows a name, a pair of commas

separates it from the rest of the sentence.

Michael Smith, paleontologist, will lead

the excavation.

Using Commas: Titles

Coordinate adjectives are adjectives that modify a noun on their own. Commas separate two or more coordinate adjectives.

It's going to be a long, hot, busy summer.

Cumulative adjectives depend on one another for meaning. Do not use commas to separate two or more cumulative adjectives.

Three large red trucks were headed for the entrance ramp.

Using Commas: Coordinate Adjectives (But Not Cumulative Adjectives)

What if you aren't sure whether you're dealing with coordinate or cumulative adjectives? Scribendi.com's editing services suggest trying these two tests:

1. If you insert the word "and" between the adjectives, does the sentence still make sense?

2. If you list the adjectives in a different order, does the sentence still make sense?

If you answered yes, you have a list of coordinate adjectives, and they should be separated by commas. If you answered no, you have a list of cumulative adjectives, and they should not be separated by commas.

An appositive is a noun or noun phrase that renames a nearby noun. The need for commas around an appositive depends on whether it is restrictive or non-restrictive.

Using Commas: Non-Restrictive Appositives (But Not Restrictive Appositives)

A non-restrictive appositive is a phrase that restates information already given.

The phrase my oldest son can only refer to one person, so the addition of his name is not necessary for us to understand the meaning of the sentence. The appositive could be removed, and we would still know who won the race. Commas are used to set apart non-restrictive appositives.

For example:

"My oldest son, Michael, won the race."

Shakespeare's play Romeo and Juliet is a classic tale of forbidden love.

Since Shakespeare wrote more than one play, we need the appositive Romeo and Juliet to clarify which play the author is discussing. If the appositive were removed, the meaning of the sentence would be unclear. Commas are not used to set apart restrictive appositives.

A restrictive appositive is a phrase that clarifies an ambiguity in the information already given.

For example:

Commas can ensure clarity and eliminate wordiness. Sometimes a comma will prevent what grammarians call mistaken junctions, when a reader groups words in a way other than that which the author intended.

Using Commas: Ensuring Clarity

Soon after the dinner was interrupted by a robbery.

She saw the spider that climbed the wall and gasped.

To Sally Frank was an insufferable person.

Soon after, the dinner was interrupted by a robbery.

She saw the spider that climbed the wall, and gasped.

To Sally, Frank was an insufferable person.

VS.

VS.

VS.

Notice the difference in clarity when commas are used properly:

The comma is a powerful punctuation mark with an impressive array of uses. No matter how the comma is used, its purpose is to make meanings clear. Authors struggling with a gray area of comma usage should consider the meaning they hope to convey and make the choice that seems best. Remember, clarity always wins out over strict adherence to comma rules.

To learn more about commas, check out GrammarCamp.com, a grammar training course that covers everything you need to know about English grammar.

To sum it all up . . .

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