The comma is a much misused and often over used piece of punctuation. The complexity of its usage stems primarily from the fact that there are several different situations in which the comma is the correct piece of punctuation to use. The trick is to identify those situations so as not to use the comma in places where it really should not be.
The following are some of the situations in which a comma should be used:
1. To separate the elements in a list of three or more items.
The potion included gobstoppers, chewing gum, bran flakes and coleslaw.
There appears to be some debate about whether or not to include a comma to separate the last two items in the series. Personally I was taught to omit the comma before the final 'and' unless there is a danger that the last two items in the series will merge and become indistinguishable without the comma.
His favourite puddings were ice apple pie, rhubarb crumble, and jelly and ice cream.
In this sentence it is acceptable to use a comma after the word crumble in order to indicate that the jelly and ice cream is considered as a single item in the series. This is called the Oxford comma. There are occasions where it is definitely needed in order to avoid unnecessary confusion. In the sentence below, the inclusion of the Oxford comma would have avoided some confusion.
I dedicate this work to my parents, Marie Smith and God.
2. Before certain conjunctions.
A comma should be used before these conjunctions: and, but, for, nor, yet, or, so to separate two independent clauses. They are called co-ordinating conjunctions.
She was a fantastic cook, but would never be as good as her mother in law.
He hated his neighbours, so he never invited them round.
A common mistake is to put the comma after the conjunction.
It is not usually necessary or indeed correct to use a comma with the conjunction 'because'.
We all had to move to higher ground because the floodwaters were rising quickly.
She really didn't feel hungry because she had already eaten a hearty lunch.
However, there are occasions when a 'because clause' needs to be set off with a comma in order to avoid any confusion of meaning.
I knew she would not be hungry, because my sister works in a restaurant and had seen her eating a huge meal earlier in the day.
In this example the reason for the person in question not being hungry is nothing to do with the sister's working in a restaurant as might be indicated if the comma were omitted.
3. To separate introductory elements in a sentence.
Use a comma to separate introductory elements in a sentence from the main part of that sentence.
Given the appalling weather conditions, Michael was lucky to survive the storm.
As the night drew to a close, the clubbers wandered home.
Having mastered the use of the colon, it is important to make it work for you in your writing.
If the introductory element of the sentence is very short, it is permissible to omit the comma. If the introductory phrase is more than about three words, the comma is recommended.
Shortly we will be leaving for the port.
After his nap Sam felt a lot better.
After a deliciously long nap in his hammock, Sam felt a lot better.
If a brief introductory phrase, however short, is likely to merge with the rest of the sentence and confuse the reader, the comma is required.
Inside the house was a total mess.
Inside, the house was a total mess.
Until the summer lectures will take place in the main building
Until the summer, lectures will take place in the main building.
The comma is also required if the introductory phrase, however short, appears to modify the meaning of the sentence.
Sadly, the whole building was beginning to crumble.
On the other hand, the new extension looked fantastic.
4. To separate parenthetical elements in a sentence.
A comma is used to set off parenthetical elements in a sentence. The parenthetical element (also known as an aside) is part of the sentence that can be removed without changing the essential meaning of the sentence.
Sarah, the most intelligent pupil in the class, was always late for school.
The pyramids, one of the wonders of the ancient world, lie just outside Cairo.
If you are using a comma to do this, it is important that the aside is opened and closed with a comma. A common mistake is to omit the second comma.
If the parenthetical element in the sentence is closely identified with the subject the comma may not be necessary.
His wife Jill was a high flyer in the city.
Jill, his wife, was a high flyer in the city.
Tick the correctly punctuated sentences.
5. To separate direct speech or quoted elements from the rest of the sentence.
Commas are used to separate direct speech or quoted elements from the rest of a sentence. Use a comma to separate the quoted material from the rest of the sentence.
"That house there," he whispered, "is where I grew up."
"Give me the money," he snarled, "unless you want to meet your maker."
Note that a comma is not always needed in direct speech if another punctuation mark serves to separate the quoted element from the rest of the sentence. Look at the following example:
"Give me the money!" he snarled.
Take care to avoid the comma splice. Look at the following example:
"That cake looks delicious," she said. "Where can I get the recipe?"
"That cake looks delicious," she said, "Where can I get the recipe?"
The two quoted elements are separate sentences and as such need to be separated by a full stop. A comma alone is not enough.
6. Commas are used to separate elements in a sentence that express contrast.
He was first attracted by her money, not her stunning looks.
She is intelligent, not pretty.
He thought the building was enormous, but ugly.
7. Commas are used for typographical reasons to separate dates and years, towns and counties etc.
His home was in Streatham, East London.
My father was born on March 13, 1949.
8. Commas are used to separate several adjectives.
The old, ramshackle, dilapidated house had a charm of its own.
That rather dull-looking, badly-dressed, clumsy man is actually a university professor.
As a general rule, if you can put the word 'and' or 'or' between the adjectives, then the comma is appropriate. If you cannot, the comma should be omitted.
The little old house was in a beautiful wood.
The comma has specific uses and, like all punctuation marks, can make your writing more precise and persuasive. Many tutors and academics complain that the comma is over used or inappropriately used. Take good care that you do not simply sprinkle your work with commas without good reason. Many people think that a pause in reading is reason enough to insert a comma. I would advise against this and only use a comma if there is a more concrete reason for doing so.
Test your understanding of the comma with this exercise.
Find out more about the comma splice.