When Do You Need a Comma?

Instructor: Shelly Merrell

Shelly has a Master's of Education. Most recent professional experience is an educational diagnostician. Prior, she taught for 8 years.

Commas are a critical part of grammar, but they can be tricky to use. In this lesson, we will learn a few of the basic rules of using a comma to make our writings clearer for readers.

Introducing the Comma

  • Let's take a picture of koalas trees and mountains.
  • I want to eat Grandma!
  • She left the states on May 21 1999.

Some of these sentences sound odd, don't they?

Let's read on to learn about applying commas in the appropriate places to make our writing easier to understand.

The Comma

The comma is a punctuation mark that indicates a soft stop, or pause, between parts in a sentence. In grammar, a comma can be used for many things like separating parts of a date, items in a list, or words that gain direct attention. In this lesson, we'll only focus on a few of the basic comma rules.


Comma in a Series

Use a comma to separate three or more words or phrases in a sentence.

  • They went to buy ice cream toppings and cake.

While ice cream toppings sounds delicious, in this sentence, it is unclear if three items were being purchased or just two.

  • They ran to get ice cream, toppings, and cake.

Now, it is obvious that three items were being purchased.

  • The zoo had roaring lions playing bears and zebras

Without commas, we might think that roaring lions are playing with bears and zebras.

  • The zoo had roaring lions, playing bears, and zebras.

With the addition of the commas, it is clear that 'playing' is describing what the bears are doing.

  • She hit the ball, ran to first base, scored, and did a happy dance.

This sentence shows how commas can be used to separate three or more phrases, the same way commas are used to separate a list of three or more.

Let's go back to the first example:

  • Let's take a picture of koalas trees and mountains.

Now we know to use the comma to separate three or more items.

  • Let's take a picture of koalas, trees, and mountains.

That makes more sense than something called koalas trees!

Coordinating Conjunctions

We also use a comma to separate parts of a sentence that can stand alone as complete thoughts when they are connected with one of seven coordinating conjunctions: for, and, nor, but, or, yet, so.

  • I wanted to go down the slide too, but I had to watch from the window.

('I wanted to go down the slide too' is one complete thought and can be a sentence by itself; the same is true of 'I had to watch from the window.')

Here's another one:

  • I didn't want to run to school, nor did I want to walk.

Introductory Phrases

Place a comma after introductory phrases that tell where, when, why, or how.

  • Last night, I went roller skating!

Did you notice the comma after we were told when?

  • Exhausted from the day, I went to bed.

The reader understands that the person was exhausted and that is why he or she went to bed.

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