Standard Accepted Guidelines for Comma Usage
Based on the Chicago Manual of Style, Bedford Handbook, Harbrace College Handbook, and Words into Type.

This is not a comprehensive list—just the most common usages you might run across. As a writer, you can choose whether or not to apply these rules to your writing. Just make sure whichever you choose to do, do it consistently. Don’t use a serial comma sometimes and not others. Either always use it or never use it. That way, when an editor sees your work, they will know you have made a deliberate choice instead of thinking you don’t know grammar well.

1. The Serial Comma. You might also hear this referred to as the Oxford comma. In a list of three or more items, a comma should precede the and:
          Please go to the store and get apples, bananas, and pears for the fruit salad.
          We came, we saw, and we conquered.
          She got up, got dressed, brushed her teeth, put on makeup, dropped the overdue books off at the library, went to the grocery store, got gas, and arrived home before her kids got out of the bed.

Exception 1: Do not use commas when all items in a series are joined by a conjunction:
          We are going to Bermuda or Jamaica or Barbados. 

Exception 2: No comma is used with an ampersand (&):
          He stepped into the offices of Folse, Bordelon & Guidry.

2. Independent Clauses. When two independent clauses (two complete thoughts that could stand alone as sentences) are joined by a conjunction (and, but, or, nor, for, so, yet, if, because*), a comma precedes the conjunction.
          The reporter turned in her story, but she missed the deadline.
          We didn’t get to go to the park, because* it was raining by the time Dad got home.
          Do you want to go swimming, or do you want to go horseback riding?

Exception 1: If the clauses are very short and very closely related, no comma is needed:
          She knelt down and she prayed.

Exception 2: If one or both of the clauses contain internal commas, use a semicolon before the conjunction:
          If you want to continue working here, Jim, we would like to keep you; but we can no longer put up with your greasy hair, ratty jeans, and Moses sandals that show off your nasty toe-jam.

*Because is a recent addition to this list and currently has the status of a style choice rather than a rule. The rule used to state that no comma came before because in a sentence, whether or not what followed it was an independent clause. However, by definition, because is a conjunction and most copy editors are beginning to treat it as such. Be careful, though, that you do not confuse it with because of, which is a preposition.

3. Introductory Phrases. Use a comma after an introductory phrase at the beginning of a sentence. These are typically adverbial (beginning with adverbs such as before, after, never, always, not, very, or –ly words) or participial (beginning with the participial form of a verb) phrases:
          At the stroke of midnight, the coach turned back into a pumpkin.
          Hoping to stop the horses, he jumped on the near one’s back and pulled the reins as hard as he could.

Exception 1: A single word or very short (2–3 words) phrase does not require a comma unless a pause is intended (when read aloud) or to avoid misreading.
         Before eating, the family always says grace. 
(not Before eating the family . . .)
          Before eating we always say grace.

Exception 2: A comma is not used after an adverbial or participial phrase that immediately precedes the verb it modifies (in other words, the phrase becomes the subject of the sentence):
          Out of the cave came the most horrific shriek.
          Growing in the median are some pretty wildflowers.<

4. Oh, Ah, Yes, No, Well, and Direct Address.  A comma follows the exclamatory oh or ah at the beginning of a sentence (before and after if it comes in the middle). A comma follows yes, no, well, or other such words at the beginning of a sentence. A comma precedes and/or follows a name/title used in direct address.
           It is, oh, such a wonderful thing!
          Well, I thought so.
          What is it, Lassie? Timmy fell down the well?
          I wonder, sir, if you would please refrain from stepping on my foot again.

Exception 1: No comma needed if it is a short phrase:
          Ah yes! Oh no! Oh well.

Exception 2: No comma is needed with the poetic O:
          O Lord, how wonderful are thy ways.

5. Restrictive and Nonrestrictive Phrases. This element includes Parenthetical Elements, Interjections, Dependent Clauses, Relative Clauses, Appositives, Not…But. If a phrase is Restrictive (i.e., necessary to the meaning of the sentence) it should not be enclosed in commas. If a phrase/clause is Nonrestrictive (i.e., supplemental information, can be left out without changing the meaning of the sentence), it is enclosed in commas.
          Brandilyn Collins, the best selling author, will be here for a book signing tomorrow. (nonrestrictive)
          Richard Armitage the British actor is young and good looking. Richard Armitage the former U.S. Deputy Secretary of State is older and not so good looking. (restrictive)
          Starbucks, which has really expensive coffee, is a national chain. (nonrestrictive)
          The book that I had to read for class is due back to the library today.(restrictive)
           (Which is typically nonrestrictive, That is usually restrictive)
          My sister, Michelle, is two years older than me. (nonrestrictive—I only have one sister)
          My mother’s sister Rinn lives in Florida. (restrictive—her sister Becky lives in North Carolina)
          It is, indeed, the most wonderful time of the year. (interjection)
          This, I think, is where we turn. (interjection)

6. Coordinate and Cumulative Adjectives. Remember these from the quiz? Coordinate adjectives are those whose order can be changed (or that can be joined by and) without changing the meaning of the phrase and they need a comma. If changing the order of the adjectives changes the meaning of the phrase, they are cumulative (or compounding) adjectives and do not need a comma.
          He was a mad, bad, dangerous-to-know man.
          He was mad, bad, and dangerous to know.
          We marveled at the enormous blue diamond necklace.

Repeated Adjectives also get a comma:
          You’re a bad, bad boy.

There are so many more rules and guidelines when it comes to commas usage (and don’t worry, we’ll get into where they go when there are quotation marks and other punctuation in a later post). This barely scratches the surface, but are most likely the most standard scenarios in which you’ll use commas in your writing. Is there a comma usage you struggle with that I haven’t listed? Something marked on your contest entry you don’t understand or disagree with? Let me know, and we’ll look into it.

Here are the rest of the answers (and explantions) for the pop quiz:

6. The Declaration of Independence, which was signed on July 4, 1776, served as the catalyst for the Revolutionary War.
    d. Comma needed after 1776.

Comma needed after 1776: While only one answer was correct on this question, there are two explanations for why the comma is needed. The first would be because the phrase which was signed on July 4, 1776 is an interjection, which is explained in the answer to question 1. It is also a rule that when a date is used in text, a comma comes before and after the year (Bedford 32i, CMS 6.48).

7. I went to the store and got asparagus and cauliflower and broccoli.
    d. No commas needed.

Items in a series joined by conjunctions: We saw a couple of examples (numbers 1 & 3) of the need for the serial comma before the and when we have a list of three or more items. However, when a series of items are all joined by conjunctions, no commas are needed (Bedford 33h, CMS 6.20). In this case, the and serves the same function as a comma in separating the items in the list, making the use of the comma unnecessary.

8. The spy betrayed not only his country but his comrades.
    d. No commas needed.

Antithetical elements: Not . . . but is one of the most difficult sentence constructions when it comes to figuring out if it needs a comma or not. The general rule of thumb goes back to the rule about restrictive and nonrestrictive phrases. If the meaning of the sentence is dependent upon the not . . . but phrases, no commas are needed. Conversely, if the not . . . but phrase is supplemental to the meaning of the sentence, two commas are needed, before the not and before the but (Bedford 32e, CMS 6.41):
    The spy’s crime was unforgivable, not only betraying his country, but also his comrades.

9. When she entered the room, she was dressed in black velvet, and she was wearing a huge, sparkling diamond necklace.
    d. Both (b) and (c).

Comma needed after room: This is the introductory phrase comma (see explanation on #2). Comma needed after velvet. This is the independent clause comma (see explanation on #2).No comma needed after sparkling. This is the cumulative adjective rule (see explanations for #s 4 & 5). The name of the object is “diamond necklace”: a diamond, huge, sparkling necklace doesn’t make sense, therefore, no comma is needed after sparkling.

Here are the answers (and explantions) for the pop quiz:

1. Football, which is called soccer in America, is very popular in South America, Europe, and Africa.
    d. Commas needed after America and Europe.

Comma needed after America: The phrase which is called soccer in America is what is called an “interjection” (CMS 6.30-31, 6.38)—basically, it’s an additional piece of information about the subject of the sentence (football). To determine whether or not a comma is needed, we first have to determine if the phrasal adjective is necessary (“restrictive”) or supplemental (“nonrestrictive”) to the sentence. If we drop the entire phrase, does it change the meaning of the sentence? Football is very popular in . . . No. So this is a nonrestrictive phrase. According to both CMS and Bedford, nonrestrictive phrases need to be enclosed in commas (or preceded by a comma if it comes at the end of the sentence). Therefore, a comma is needed after America, to enclose this nonrestrictive phrase.

Comma needed after Europe: This is a rule that is most controversial when it comes to commas: the serial comma. Many people probably did not think that a comma was needed here. If this sentence appeared in a newspaper or magazine, you would be right. It is journalistic style (AP Stylebook) to drop the serial comma. However in academic and fiction writing, 99% of the time, you will find the serial comma is expected (Bedford 32c, CMS 6.19). What is the definition of a serial comma? It is the comma that comes before the and in a list of three or more items: apples, bananas, and oranges. In an example below, we will see how the omission of the serial comma actually changes the meaning of the sentence!

2. After lunch, the jury was called back to the courtroom, and they heard testimony on behalf of the defendant.
    d. Commas needed after lunch and courtroom.

Comma needed after lunch: Introductory phrases are followed by commas (Bedford 32b, CMS 6.25). Why? To quote from Bedford: “A comma tells readers that the introductory clause or phrase has come to a close and that the main part of the sentence is about to begin” (pg. 427). To give another example:
    After she finished eating her dog got all the scraps.
She ate her dog???? Of course not! It should read:
    After she finished eating, her dog got all the scraps.
See how one little piece of punctuation makes all the difference?

Comma needed after courtroom: This is the “independent clause” comma. When two independent clauses (two clauses that could stand alone as complete sentences) are joined by a coordinating conjunction (and, but, or, nor, for, so, yet, and because), a comma should precede the conjunction (Bedford 32a, CMS 6.32). The comma signals the end of one complete clause and the beginning of the next. Exception: if the sentences are very short and very closely related, the comma can be omitted. (e.g., We came and we saw him.)

3. We went to the store, ate, and got gas.
    b. Comma needed after ate.

Serial comma needed: Remember above when I said we’d see how a serial comma can change the meaning of a sentence? With no serial comma in this sentence, the and joins got gas only to ate-–it indicates that the we subject of the sentence only did two things (went to the store and ate) and that the last piece (got gas) is part of the second (ate). Hopefully whoever this “we” is carries some Beano around with them! I wonder if they had Mexican food.

4. It was a dark, stormy night.
    a. No changes needed; sentence is correct.

5. We saw an endangered black rhino.
    a. No changes needed; sentence is correct.

More than one adjective: Whether or not to put a comma between adjectives can be super-confusing . . . unless you learn the secret grammarians (and English majors) around the world learned long ago: switch the adjectives around. If you can change the order of the adjectives without changing the meaning of the phrase, then they are coordinate adjectives and need a comma. If changing the order of the adjectives changes the meaning of the phrase, they are cumulative (or compounding) adjectives and do not need a comma. (Bedford 32d, CMS 6.39)
     It was a dark, stormy night is the same as It was a stormy, dark night. Therefore, the comma is necessary.
     We saw an endangered black rhino is not the same as We saw a black, endangered rhino. “Black rhino” is the name of the animal, which is actually a brownish gray color, therefore, the second sentence changes the meaning.

Reading over these explanations, do you want to change any of your answers for numbers six through ten?

Commas seem to be one of the most daunting pieces of the grammar landscape that any writer deals with. And depending on whether you’re writing academic papers, novels, non-fiction, or newspaper/magazine articles, the rules can differ. However, using a “strict” method will never steer you wrong. For the discussion of punctuation, especially commas, I’ll be referring to rules in the Chicago Manual of Style 15th Edition and the Bedford Handbook 5th Edition and using examples inspired by the book Eats, Shoots & Leaves.

Let’s start out with a pop-quiz, just to see where everyone is. You can post a comment with your answers or you can keep them to yourself, if you’d like. Answers will be posted tomorrow.

1. Football, which is called soccer in America is very popular in South America, Europe and Africa.
    a. No changes needed; sentence is correct.
    b. Comma needed after Europe.
    c. Comma needed after America.
    d. Commas needed after America and Europe.

2. After lunch the jury was called back to the courtroom and they heard testimony on behalf of the defendant.
    a. No changes needed; sentence is correct.
    b. Comma needed after lunch.
    c. Comma needed after courtroom.
    d. Commas needed after lunch and courtroom.

3. We went to the store, ate and got gas.
    a. No changes needed; sentence is correct.
    b. Comma needed after ate.
    c. No comma needed after store.
    d. Comma needed after and.

4. It was a dark, stormy night.
    a. No changes needed; sentence is correct.
    b. Comma needed after stormy.
    c. Comma needed after was.
    d. No comma needed.

5. We saw an endangered black rhino.
    a. No changes needed; sentence is correct.
    b. Comma needed after saw.
    c. Comma needed after saw and endangered.
    d. Comma needed after endangered.

6. The Declaration of Independence, which was signed on July 4, 1776 served as the catalyst for the Revolutionary War.
    a. No changes needed; sentence is correct.
    b. No comma needed after Independence.
    c. Comma needed after signed.
    d. Comma needed after 1776.

7. I went to the store and got asparagus, and cauliflower, and broccoli.
    a. No changes needed; sentence is correct.
    b. No comma needed after asparagus.
    c. No comma needed after cauliflower.
    d. No commas needed.

8. The spy betrayed, not only his country, but his comrades.
    a. No changes needed; sentence is correct.
    b. No comma needed after betrayed.
    c. No comma needed after country.
    d. No commas needed.

9. When she entered the room she was dressed in black velvet and she was wearing a huge, sparkling, diamond necklace.
    a. No changes needed; sentence is correct.
    b. Commas needed after room and velvet.
    c. No comma needed after sparkling.
    d. Both (b) and (c).

10. The writer who was recently signed to a multi-book contract will be here for a book signing on August 28.
    a. No changes needed; sentence is correct.
    b. Commas needed after writer and contract.
    c. Commas needed after writer and signing.
    d. Commas needed after contract and August.