an icon showing a commaCommas: these little demons haunt the nightmares of many a professor after an evening of reading student papers. It seems nearly impossible to remember and apply the seventeen or so comma rules that seem to given out as the standard. (For example: “Use commas to set off independent clauses joined by the common coordinating conjunctions.” or “Put a comma before the coordinating conjunction in a series.”)

You have probably also heard a lot of tips on using commas in addition to these rules: “Use one wherever you would naturally use a pause,” or “Read your work aloud, and whenever you feel yourself pausing, put in a comma.” These techniques help to a degree, but our ears tend to trick us, and we need other avenues of attack.

Perhaps the best and most instructive way for us to approach the comma is to remember its fundamental function: it is a separator. Once you know this, the next step is to determine what sorts of things generally require separation. This includes most transition words, descriptive words or phrases, adjacent items, and complete ideas (complete ideas contain both a subject and a verb).

Transition Words

Transition words add new viewpoints to your material; commas before and after transition words help to separate them from the sentence ideas they are describing. Transition words tend to appear at the beginning or in the middle of a sentence. By definition, a transition word creates context that links to the preceding sentence. Typical transition words that require commas before and after them include however, thus, therefore, also, and nevertheless.

  • Therefore, the natural gas industry can only be understood fully through an analysis of these recent political changes.
  • The lead prosecutor was prepared, however, for a situation like this.

Note: As was mentioned, these words require commas at the beginning or middle of a sentence. When they appear between two complete ideas, however, a period or semicolon is required beforehand:

  • Clint had been planning the trip with his kids for three months; however, when work called he couldn’t say no.
  • Sam was retired. Nevertheless, he wanted to help out.

As you can see from these examples, comma is always required after transition words.

Descriptive Phrases

Descriptive phrases often need to be separated from the things that they describe in order to clarify that the descriptive phrases are subordinate (i.e., they relate to the sentence context, but are less responsible for creating meaning than the sentence’s subject and verb). Descriptive phrases tend to come at the very beginning of a sentence, right after the subject of a sentence, or at the very end of a sentence.

  • Near the end of the eighteenth century, James Hutton introduced a point of view that radically changed scientists’ thinking about geologic processes.
  • James Lovelock, who first measured CFCs globally, said in 1973 that CFCs constituted no conceivable hazard.
  • All of the major industrialized nations approved, making the possibility a reality.

In each example, the phrase separated by the comma could be deleted from the sentence without destroying the sentence’s basic meaning. If the information is necessary to the primary sentence meaning, it should not be set off by commas. Let’s look at a quick example of this:

  • Jefferson’s son, Miles, just started college.
  • Jefferson’s son Miles just started college

You would write the first sentence if Jefferson only has one son and his name is Miles. If Jefferson only has one son, then Miles is not needed information and should be set off with commas.

You would write the second sentence if Jefferson has multiple sons, and it is his son Miles who just got into college. In the second sentence, Miles is necessary information, because until his name is stated, you can’t be sure which of Jefferson’s sons the sentence is talking about.

This test can be very helpful when you’re deciding whether or not to include commas in your writing.

Adjacent Items

Adjacent items are words or phrases that have some sort of parallel relationship, yet are different from each other in meaning. Adjacent items are separated so that the reader can consider each item individually.

The river caught fire on July 4, 1968, in Cleveland, Ohio.

The dates (July 4, 1968) and places (Cleveland, Ohio) are juxtaposed, and commas are needed because the juxtaposed items are clearly different from each other. This applies to countries as well as states: “Paris, France, is beautiful this time of year.”


The commas have been removed from the following sentences. Re-type them, adding the correct commas back in.

  1. Sergi Sousa the top-ranked shoe designer in Rhode Island is going to be at the party tonight.
  2. Sergi only wears shoes that he created himself.
  3. Nevertheless he is incredibly courteous and polite to everyone he meets.
  4. He was born in Barcelona Spain on April 19 1987.

Coordinating Conjunctions: FANBOYS

We learned about coordinating conjunctions earlier in the course. These are words that join two words or phrases of equal importance. The mnemonic FANBOYS helps us remember the seven most common: for, and, nor, but, oryet, and so.

When these conjunctions join two words or phrases, no comma is necessary (for more than two, take a look at “Commas in Lists” just below):

  • Paula and Lucca had a great time on their date.
    • “Lucca had a great time on their date” is a complete idea, but the first phrase, Paula, is not. No comma is required before and.
  • Minh turned off the lights but left the door unlocked.
    • “Minh turned off the lights” is a complete idea; “left the door unlocked.” No comma is required before but.
  • Danny studied the lifespan of rhinoceroses in their native Kenya and the lifespan of rhinoceroses in captivity.
    • “Danny studied the lifespan of rhinoceroses in their native Kenya” is a complete idea; “the lifespan of rhinoceroses in captivity” is not. No comma is required before and.

When these conjunctions are used to join two complete ideas, however, a comma is required:

  • We could write this as two separate sentences, but we’ve chosen to join them together here.
    • Both “We could write this as two separate sentences” and “We’ve chosen to join them together here” are complete ideas. A comma is required before the but.


The commas have been removed from the following sentences. Re-type them, adding the correct commas back in.

  1. Aamir and Tyesha went on a trip to California.
  2. Aamir was nervous but Tyesha was excited.
  3. They had been to East Coast before but never to the West.
  4. Aamir became less nervous after he looked up a few tourist guides and journals online.
  5. When they came home Tyesha had not enjoyed herself but Aamir had.

Commas in Lists

The serial comma is used to separate adjacent items—different items with equal importance—when there are three or more. This is so the reader can consider each item individually. Let’s look at a few examples

  • Weathering may extend only a few centimeters beyond the zone in fresh granite, metamorphic rocks, sandstone, shale, and other rocks.
  • This approach increases homogeneity, reduces the heating time, and creates a more uniform microstructure.

In the first sentence, the commas are important because each item presented is distinctly different from its adjacent item.  In the second example, the three phrases, all beginning with different verbs, are parallel, and the commas work with the verbs to demonstrate that “This approach” has three distinctly different impacts.

The Serial Comma (a.k.a the Oxford Comma)

Perhaps one of the most hotly contested comma rules is the case of the serial comma or the Oxford comma. MLA style (as well as APA and Chicago) requires the use of the serial comma—AP style highly recommends leaving it out. But what is the serial comma?

The serial comma is the comma before the conjunction (andor, and nor) in a series involving a parallel list of three or more things. For example, “I am industrious, resourceful, and loyal.” The serial comma can provide clarity in certain situations. For example, if the and is part of a series of three or more phrases (groups of words) as opposed to single words:

Medical histories taken about each subject included smoking history, frequency of exercise, current height and weight, and recent weight gain.

The serial comma can also prevent the end of a series from appearing to be a parenthetical:

I’d like to thank my sisters, Beyoncé and Rhianna.

Without the serial comma, it may appear that the speaker is thanking his or her two sisters, who are named Beyoncé and Rhianna (which could be possible, but isn’t true in this case). By adding the serial comma, it becomes clear that the speaker is thanking his or her sisters, as well as the two famous singers: “I’d like to thank my sisters, Beyoncé, and Rhianna.”

By always using a comma before the and in any series of three or more, you honor the distinctions between each of the separated items, and you avoid any potential reader confusion.

Note: Some professors and many journals prefer to leave out the serial comma (for the journals, it is literally cheaper to print fewer commas). Because of this, the serial comma is not recommend in AP style.


The commas have been removed from the following sentences. Re-type them, adding the correct commas back in.

  1. Ava’s favorite meals are cauliflower soup steak and eggs lasagna and chicken parmigiana.
  2. Victor tried to make dinner for her. Unfortunately his skills are mostly limited to eating buying or serving food.
  3. Victor and Ava decided to choose a restaurant and go out to eat.

Comma Overuse

A sure way to irritate educated readers of your work is to give them an overabundance of commas. It is easy but dangerous to take the attitude that Sally once did in a Peanuts comic strip, asking Charlie Brown to correct her essay by showing her “where to sprinkle in the little curvy marks.”

Perhaps the best way to troubleshoot your particular comma problems, especially if they are serious, is to identify and understand the patterns of your errors. We tend to make the same mistakes over and over again; in fact, many writers develop the unfortunate habit of automatically putting commas into slots such as these:

  • between the subject and verb of a sentence
  • after any number
  • before any preposition
  • before or after any conjunction


Read the following sentences. How many of them have unnecessary commas? Type your corrected sentences in the text frame below?

  1. The bushings, must be adjusted weekly, to ensure that the motor is not damaged.
  2. Many botanists still do not fully appreciate these findings even after 22 years, following the publication of the discovery paper.
  3. Other manufactured chemicals that also contain bromine are superior for extinguishing fires in situations where people, and electronics are likely to be present.
  4. The price of platinum will rise, or fall depending on several distinct factors.

Just as it is common for someone to have to look up the same tricky word dozens of times before committing its proper spelling to memory, you may need to reference comma rules multiple times before they feel natural to use. As with spelling, commas (or the absence of commas) must be repeatedly challenged in your writing.

As you perfect your comma usage, you will learn to recognize and reevaluate your sentence patterns, and the rewards are numerous. There is no foolproof or easy way to exorcise all of your comma demons, but a great place to start is reminding yourself of the comma’s basic function as a separator and justifying the separation of elements. In the end, you simply must make a habit of reading, writing, and revising with comma correctness in mind.