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Commas are important.  Consider the following sentences:

  • Let’s eat, Grandma.
  • Let’s eat Grandma.

Perhaps the best way to determine comma use is to remember the comma’s fundamental function: it is a separator. Once you know this, the next step is to determine what sorts of things generally require separation using commas:

  • lists
  • transition words
  • descriptive words and phrases
  • dates and places


Use commas to separate items in a list, e.g.:

  • Four-year-old Harry liked hot dogs, real dogs, and dog-eared pieces of paper.
  • Pick up milk, bread, butter, eggs, fruit, and sausage for breakfast tomorrow.

Note that there is a comma before the “and” in the sentences above.  Using a comma before the linking word and last list item is actually a debated issue (among grammarians, at least).  That last comma before the linking word and last item is called an Oxford comma and/or a serial comma.  It’s good to get used to using it, because there are situations in which that last comma really helps to clarify the sentence.

The following example is adapted from an actual coupon for a restaurant that offered four breakfast sandwich options – cheese, vegetable, bacon, and sausage:

  • This coupon is good for cheese, vegetable, bacon and sausage breakfast sandwiches.

Without that last comma, it seems that the restaurant offers a sandwich containing both bacon and sausage.

Here’s another example, from a speech in which an award recipient is thanking her sisters as well as the performers Beyoncé and Rhianna, who both aided her career:

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

Without that last comma, it seems as though Beyoncé and Rhianna are the award recipient’s sisters instead of the performers.

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 potential confusion.

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:

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

Note: As we mentioned, transition 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.

Descriptive Phrases

Descriptive phrases often need to be separated from the things they describe. Descriptive phrases tend to occur 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.

Dates and Places

Use a comma to separate day and year, and to separate year from the rest of the sentence, if more of the sentence follows.

Use a comma to separate a city and state, and to separate the state from the rest of the sentence, if more of the sentence follows.

For example:

  • The river caught fire on July 4, 1968, in Cleveland, Ohio.
  • We visited New Paltz, New York, on our tour of SUNY Colleges.

For additional explanations and examples, view the following video.

Note: Some content in the video “#Grammar Doctor – Comma Rules” is presented visually. You may listen to this video with audio description.


The commas have been removed from the following sentences. Retype 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.

Because comma use is so important, here’s some additional practice.


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

  1. Victor and Ava were house-sitting for Ava’s uncle while he was on vacation.
  2. Ava had purchased food at a grocery store and Victor decided to cook Ava one of her favorite meals.
  3. Ava’s favorite meals are cauliflower soup steak and eggs lasagna and chicken parmigiana.
  4. Victor thought about the work needed for each meal. Unfortunately his skills were mostly limited to eating buying or serving food.
  5. Victor and Ava decided to choose a restaurant and go out to eat.