Commas are important punctuation marks in written English and knowing how to use them correctly will help you to become a better writer. They are also one of the most misused punctuation marks, so read on to learn how to use commas correctly and avoid mistakes.

Separating Items in a Series

Commas should be used to separate each item in a series of three or more, except for the last one. Let’s look at an example.

Shondra’s favorite cities are Boston, Chicago, and Toronto.

So, this sentence contains three items: Boston, Chicago, and Toronto. Notice the comma after the first two. A period is needed after the last one because it is the last word in the sentence.

Note, however, that a series that contains only two items should not contain a comma.

Shondra’s favorite cities are Boston and Toronto.

You will sometimes see sentences with series in which a comma is omitted after the next-to-last item. This is more of a journalism style common in newspapers and magazines. However, traditionally, a comma is placed after each item except for the last one.

Also, keep in mind that the items in a series may contain more than just one word.

Every Saturday, my friends and I meet at Starbucks for a coffee, go to the mall to shop, and then have lunch at our favorite pub.

After the Names of Cities and States

A comma is always place after the names of cities when followed by either the name of a state or country.

We found many great restaurants to enjoy in Osaka, Japan, last summer.

Also, notice the comma after the name of the country. Yes, a comma is needed there as well. So, we place a comma after the name of the city, and the country if the sentence continues.

The same applies to city-state pairs.

We should make it to Lexington, Kentucky, by sundown if we don’t too many stops along the way.

With Dates

Be sure to place a comma after the name of a month and the day of the month. Also, place one after the year if the sentence continues.

Shellie opened her business on March 17, 2012, and it is very successful to this day.

It’s very common to forget the comma after the year, but one is necessary to be entirely correct. However, if only a month and year are used (with no day), then no comma is needed after the month.

Jason’s birthday is in September 1975, but I am not sure of the day.

Following Introductory Elements

Introductory elements set up a sentence for what is follow, usually the main point of the sentence. You can usually spot introductory elements by looking for the following words:

after, although, as far as, as soon as, because, before, now that, once, since, though, unless, until, when, whenever, where, wherever, while

A comma often does for us in written English what our voices do for us in spoken English. As you read a sentence aloud, note where the natural pauses in your voice occur. It is usually there that a sentence is needed.

As we entered the conference room, a loud cheer suddenly erupted.

If you read the sentence above aloud, you will notice your voice naturally wants to pause after the word “room.” Therefore, it is here that a comma is needed in the written sentence.

Unless you have any questions, you may go ahead and start.

It would sound awkward to say this sentence aloud without the pause after the word “questions;” thus, it would also look awkward (and would be confusing) to leave off the comma in its written form.

After Transitions and the Phrase “For Example”

Commas should always be placed after words known as transitions. These are words to lead into a new sentence or paragraph. Examples of transition words include:

however, therefore, thus, additionally, in addition, on the other hand, first, second, third, finally, in conclusion, moreover

It’s a good idea in general to use transitions at the beginning of a new paragraph or when switching topics in a sentence.

I like Jenna’s idea so far; however, I need more details before a finally decide.

Notice the semi-colon before the transition word “however” and the comma after it.

In addition to transitions, place a comma after the phrase “for example.” 

For example, there’s a nice cafe right at the end of the street.

Also, place a comma before this phrase if it comes at the end of a sentence.

You can choose between a green one and an orange, for example.

To Set Off Nonessential Clauses

Sometimes, a sentence will contain a clause (a “chunk” of a sentence) that provides more information or serves as an example but is not absolutely necessary for the sentence to still make perfect sense. We need to set these off by placing a comma both before and after them.

The boy’s father, who moved to Boston at the age of 15, was awarded the prize by the mayor.

We could have just written

The boy’s father was awarded the prize by the mayor.

This sentence is still perfectly clear and logical. The clause that is separated by commas — “, who moved to Boston at the age of 15,” — adds some interesting information, but is not critical for understanding the sentence. 

There are many other uses for a commas but the points in this post will help you learn how to use commas in the five cases discussed here.