Basic Rules for Using Commas
The purpose of the comma is to prevent confusion. Without commas, readers would often find themselves half-way through a sentence before realizing they have read it wrong, and they would then need to re-read the sentence.
For instance, the following sentence, which contains no comma, could cause the reader to backtrack:
“As Jennifer walked on her cat followed.”
Many readers would misinterpret these words to mean that Jennifer walked on top of her cat. Then, realizing that the sentence doesn’t make sense, they would need to start over.
A simple comma makes a world of difference:
“As Jennifer walked on, her cat followed.”
The comma makes the reader mentally pause after the word on, not after cat. There is now very little chance of confusion.
This article outlines some of the most basic rules for using commas correctly to ensure your readers do not become confused.
1) Commas come between independent clauses.
When a sentence contains two clauses, each of which could stand alone as its own sentence, a comma is required before the conjunction.
Incorrect: “We played basketball and we played volleyball.”
Correct: “We played basketball, and we played volleyball.”
However, when the phrase after the conjunction could not stand alone as a sentence, it is incorrect to use a comma.
Incorrect: “We played basketball, and volleyball.”
Correct: “We played basketball and volleyball.”
2) Commas come after introductory phrases.
This rule does not need to be followed one hundred percent of the time, but you can’t go wrong by using it. Thus, when in doubt, use a comma after an introductory phrase.
A sentence which requires a comma after the introductory phrase was seen earlier in this article:
“As Jennifer walked on, her cat followed.”
As we saw earlier, omitting the comma can easily lead to confusion, and so it is mandatory.
Failing to insert a comma after an introductory phrase can be particularly confusing if the introductory phrase is long. Compare the two sentences below and notice how much easier it is to read with a comma:
Incorrect: “After spending more than half the day doing chores that I really didn’t want to do today I finally had time to eat something.”
Correct: “After spending more than half the day doing chores that I really didn’t want to do today, I finally had time to eat something.”
The introductory phrase in this sentence is so long that it is easy for the reader to incorrectly blend it into the rest of the sentence. The comma signals that the reader should take a needed pause.
There are times when a comma is not required after an introductory phrase. When the introductory phrase is short and there is no potential for the reader to be confused, the comma may be omitted (though it does not have to be).
Correct: “After lunch I’m going for a walk.”
Also correct: “After lunch, I’m going for a walk.”
3) Commas separate transitional phrases and additional information from the rest of the sentence.
When a transitional word or phrase — such as therefore or in other words — is used to link a sentence to the sentence which precedes it, a comma should be placed after the transitional word or phrase in most cases.
Incorrect: “I forgot to add baking powder. Because of that the cake did not rise.”
Correct: “I forgot to add baking powder. Because of that, the cake did not rise.”
The comma signals the natural pause that would occur if one were to say the sentence aloud. For single words acting as transitions, the comma may be omitted, particularly if you would not pause after the word if you were saying the sentence out loud.
Correct: “Of course you could come by for a visit any time on Sunday”
Also correct: “Of course, you could come by for a visit any time on Sunday”
4) Commas separate parts of full dates and locations.
The convention for writing full dates and locations is to insert commas between the individual parts of the date or location. For full dates, commas are inserted after the day of the week and (if the year is also given) after the date itself.
Incorrect: “You are required to pay the rest of your fee before Friday September 29 2017.”
Correct: “You are required to pay the rest of your fee before Friday, September 29, 2017.”
Commas must separate names of cities from names of regions and from names of countries.
Incorrect: “I live in Toronto Ontario Canada.”
Correct: “I live in Toronto, Ontario, Canada.”
5) Commas set off interjections and the names of addressees.
When interjections are not so pronounced that they are followed by an exclamation point, they should be followed by a comma to create a pause before the rest of the sentence.
Incorrect: “Oh I didn’t see you there.”
Correct: “Oh, I didn’t see you there.”
The same applies to the non-interjections yes and no.
Incorrect: “No I don’t think so.”
Correct: “No, I don’t think so.”
Also, when you name the person or a group of people that is being addressed, the word used to address the person or group must be set off by commas on both sides.
Incorrect: “Please, Sally can you give me another chance?”
Also incorrect: “Please Sally, can you give me another chance?”
Correct: “Please, Sally, can you give me another chance?”
There are other uses for commas, but the rules regarding these are quite complex. Thus, other uses for commas will be discussed in the next articles in this series.
Jake Magnum, author of the Magnum Proofreading Tips blog, is dedicated to helping writers perfect their work. In addition to giving free advice on his blog, Jake helps writers by offering very affordable proofreading services at magnumproofreading.com.