Commas: Learn It 1

  • Demonstrate how to use commas as separators
  • Demonstrate how to use commas with conjunctions and in lists
  • Recognize the correct uses of commas

Commas as Separators

In writing, commas act as dividers that set apart ideas, details, or transitions to prevent confusion.

Transition Words

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 of a sentence, but they can also be found in the middle or at the end.

Transitions

  • 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.
  • The use of commas does not need to be difficult, however.

When transition words appear between two independent clauses (or two sentences that could stand alone), however, a period or semicolon is required beforehand.

Transitions between independent clauses

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

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

The key here is to ask yourself whether the transition word connects two sentences.

Does it connect two sentences?

  • The food, however, is delicious.

“The food” is not a complete sentence, nor is “is delicious.”

  • The food is delicious; however, I am full.
  • The food is delicious. However, I am full.

“The food is delicious” is a complete sentence. “I am full” is a complete sentence.

Descriptive Phrases

Descriptive phrases add extra information about the nouns they describe, and they are usually set off with commas. If the extra information can be removed without changing the core meaning of the sentence, it should be separated by commas.

  • Near the end of the eighteenth century, James Hutton introduced a point of view that radically changed scientists’ thinking about geologic processes.
    • The phrase “Near the end of the eighteenth century” is extra information and is correctly separated by a comma.
  • James Lovelock, who first measured CFCs globally, said in 1973 that CFCs constituted no conceivable hazard.
    • The phrase “who first measured CFCs globally” adds extra information about James Lovelock and is enclosed in commas.
  • All of the major industrialized nations approved, making the possibility a reality.
    • The phrase “making the possibility a reality” explains the result of the approval and is correctly separated by a comma.

If the descriptive phrase contains information that is necessary to identify the subject, it should not be set off by commas.

Consider the difference in the following sentences:

  • My sister, who is beautiful and brilliant, is ten years older than I am.
    • The phrase “who is beautiful and brilliant” is extra and removable—it’s an additional detail, it’s not essential to know which sister is being referred to.
  • My sister, who is ten years older than I am, is beautiful and brilliant.
    • The phrase “who is ten years older than I am” is only extra if you have one sister. If you have multiple sisters, this phrase identifies which sister, so it should not be enclosed in commas.

A name or phrase should not be set off by commas if it is essential to identify the person or thing being discussed.

For these examples, let’s say you have three sisters and one brother:

  • My sister Susan is a great baseball player.
    • The name “Susan” is essential information because you have multiple sisters. No commas are used.
  • My brother, Ilton, is a fantastic piano player.
    • Since you have only one brother, his name is not essential to identify him, so commas are appropriate.

One way to test if a phrase is nonessential (and should be set off by commas) is to see if the sentence still makes sense when the phrase is removed.

  • My sister, Susan, is a great baseball player.

    • Removing “Susan” gives us: My sister is a great baseball player. If this version is unclear (because you have more than one sister), then the commas are incorrect. Therefore, My sister Susan is a great baseball player.” is correct. 

Commas with Dates and Locations

We use commas with dates, between a city and state in the United States, and cities and other countries. Consider the following examples:

  • The river caught fire on July 4, 1968, in Cleveland, Ohio.
  • Paris, France, is beautiful this time of year.