Punctuation

The Comma

The comma is the most misused punctuation mark. This is probably because there are several uses for the comma, and it’s hard to remember all of them. This section will review the comma’s uses, offer examples of those uses, and highlight the most common comma mistakes.

Comma Rule #1: Combining Independent Clauses

Use a comma before a conjunction that joins two independent clauses. In simpler terms:

A conjunction is a connecting word. It is used to link two words or groups of words. A good acronym for remembering the seven most common conjunctions is FANBOYS: for, and, nor, but, or, yet, so.

Other Common Conjunctions: because, since, as, while, although, even though, though, nor, whereas

Think of an independent clause as a complete thought or a complete sentence. It can stand on its own and make sense.

So, when you've got a conjunction, and there is a complete thought on both sides of that conjunction, you need to use a comma. If there is not a complete thought on both sides of the conjunction, no comma is necessary.

Usage Examples

1. Many developing countries need agriculture , but  their farmers often lack adequate tools and supplies.
(a complete thought)   (a complete thought)
  • But is the conjunction.
  • "Many developing countries need agriculture" is a complete thought.
  • "Their farmers often lack adequate tools and supplies " is a complete thought.
  • A comma is needed before but.
2. It is important to communicate effectively , for  the world is becoming a more interconnected place.
(a complete thought)   (a complete thought)
  • For is the conjunction.
  • "It is important to communicate effectively" is a complete thought.
  • "The world is becoming a more interconnected place" is a complete thought.
  • A comma is needed before for.
3. Agronomists study soil  and  develop ways to protect it from erosion.
(a complete thought)   (an incomplete thought)
  • The conjunction is and.
  • "Agronomists study soil" is a complete thought.
  • "Develop ways to protect it from erosion" is not a complete thought. It doesn't make sense on its own.
  • A comma is not needed before and.

Comma Rule #2: After an Introductory Clause

Use a comma after an introductory clause (a group of words that leads into the main part of the sentence). An introductory clause will not be able to stand on its own as a complete thought.

Usage Examples

1. When the dam breaks , there will be mass flooding.
(an incomplete thought) (a complete thought)

 

2. Beneath the soil,  ancient artifacts were discovered.
(an incomplete thought) (a complete thought)

 

3. When a new species is introduced into an ecosystem , the entire ecosystem can become vulnerable.
(an incomplete thought) (an incomplete thought)

 

Comma Rule #3: Separating Items in a Series

Use a comma to separate items in a series.

Usage Examples

  1. Deer, moose, pheasants, and many other animals make their habitats on farmland.
  2. Agronomy involves the sciences of biology, chemistry, and ecology.
  3. The farmer plans on milking the cows, watering the animals, and plowing the field.

Comma Rule #4: Setting Off Non-Essential Information

Use a comma before and after nonessential information. Nonessential information is a word or phrase that interrupts a sentence, oftentimes to provide more information. If you take a it out of the sentence, the sentence still maintains its same basic meaning. You can also think of nonessential elements as interrupters.

Other Common Conjunctions: because, since, as, while, although, even though, though, nor, whereas

Usage Examples

1. Ethanol which is a biofuel , is made from corn and a variety of grains.
  (interrupter)  

The interrupter can be eliminated: Ethanol is made from corn and a variety of grains.

 

2. Food borne illnesses,  like Salmonella , can result from poor handling or inadequate storage of food.
  (interrupter)  

The interrupter can be eliminated: Food borne illnesses can result from poor handling of food or inadequate storage of food.

 

3. Rural development initiatives,  such as government loans , are important for local food economies.
  (interrupter)  

The interrupter can be eliminated: Rural development initiatives are important for local food economies.

 

4. No, clover is not a grass.
(interrupter)

The interrupter can be eliminated: Clover is not a grass.

 

5. Well, if clover is not a grass, is it a forb?
(interrupter)

The interrupter can be eliminated: If clover is not a grass, is it a forb?

 

Comma Rule #5: Separating Multiple Adjectives

Use a comma between two or more adjectives (describing words) that modify the same noun. In other words, if you have two or more adjectives describing the same noun, you need to separate those adjectives with a comma.

A good rule of thumb is to use a comma if the adjectives could also be connected with "and".

Usage Examples

  1. Laboratory work can be a grueling, tedious job.
    • Grueling and tedious are both adjectives.
    • Grueling and tedious both describe job.
    • In accordance with our rule of thumb, you could reword the sentence as such: "Laboratory work can be a grueling and tedious job."
  2. Big Bluestem is a tall, reddish grass that can grow in many environmental conditions.
    • Tall and reddish are both adjectives.
    • Tall and reddish both describe grass.
    • In accordance with our rule of thumb, you could reword the sentence as such: "Big Bluestem is a tall and reddish grass that can grow in many environmental conditions."
  3. Detasseling corn is laboriousfilthy, tiresome work.
    • Laborious, filthy and tiresome are all adjectives.
    • Laborious, filthy and tiresome all describe work.
    • In accordance with our rule of thumb, you could reword the sentence as such: "Detasseling corn is laborious and filthy and tiresome work."

Comma Rule #6: Addressing Someone

Use commas when addressing someone/something directly.

Usage Examples

  1. Class, please put away your materials.
  2. Listen, people, I need you to concentrate.
  3. When will a prairie burn be necessary, Dr. Waters?

Comma Rule #7: Before/After Direct Quotations

Use a comma to set off direct quotations from the rest of a sentence.

Usage Examples

  1. Explaining his position on global warming, Al Gore asserts, "I don't really consider this a political issue. I consider it to be a moral issue."
  2. "The reality," states Garcia"is that there are no easy solutions."
  3. "Imagination is more important than knowledge," said Einstein.

Common Comma Mistakes

  1. Placing a comma before a conjunction when the conjunction does not join independent clauses (see Comma Rule #1).

     

    Example:  Procrastinating can cause a person stress , and  will probably lower the quality of his/her work,
      (a complete thought)   (an incomplete thought)

    Correct: Procrastinating can cause a person stress and will probably lower the quality of his/her work.

  2. Omitting a comma before a conjunction that joins two independent clauses (see Comma Rule #1).

     

    Example:  The oil spill continued for several months  and  its consequences were devastating.
      (a complete thought)   (a complete thought)

    Correct: The oil spill continued for several months, and its consequences were devastating.

  3. Using a comma to join two complete thoughts (sentences) — you must use a conjunction with a comma in order to join two complete sentences. Using only a comma will result in a run-on sentence.

     

    Example:  We did some fieldwork it was a good learning experience.
      (a complete thought) (a complete thought)

    Correct: We did some fieldwork, and it was a good learning experience.

  4. Using a comma that separates the subject (who/what the sentence is about) from the verb.

     

    Example:  The Midwestern states , are now considered leaders in wind energy.
      (subject) (verb)

    Correct: The Midwestern states are now considered leaders in wind energy.

  5. Using commas randomly — remember: a comma should have a purpose. Think of commas as road signs that help guide your reader through a sentence. After all, without proper comma placement, sentences can take on multiple meanings or can even be confusing to readers.

The following examples demonstrate why commas have a place (literally!) in writing.

  1. Incorrect: To survive a war must be waged.
    Correct: To survive, a war must be waged.
  2. Incorrect: For most other people can sometimes be hard to read.
    Correct: For most, other people can sometimes be hard to read.
  3. Incorrect: Several weeks before a tornado leveled the town.
    Correct: Several weeks before, a tornado leveled the town.
  4. Incorrect: Inside the child was nervous.
    Correct: Inside, the child was the nervous.