Commas – how (and how not) to use them 

The main purpose of commas is to make the meaning of a sentence clear. If a comma is omitted or inserted in the wrong place, it can change the meaning of a sentence, so it does not appear as the writer intended. Similarly, if a comma is inserted when not necessary, it can also change the meaning. Look at this example about instructions given in an email from a householder to a decorator: 

Please paint the door red and green, for the window frames also need to be painted. 

The householder was surprised to return home to find that the door had been painted in alternate red and green stripes!  The window frames had not been painted at all. When the householder complained to the decorator, he replied, ‘This is what you told me to do, but you didn't tell me what colour the window frames are to be, so I left them to wait for further instructions.’ This happened because the householder put the comma in the wrong place. The sentence should have been. 

Please paint the door red, and green for the window frames which also need to be painted. 

Although there are grammar rules for the use of commas, these are flexible. This is because fashions and trends change, and also because the use of commas is sometimes a matter of personal preference. If you have written a piece of work, whether it be a dissertation or a novel, a good way to test if you have used commas correctly is to read the piece aloud to yourself (or to another person) and ask yourself ‘Does this make sense?’ or ‘Is it clear?’ When reading aloud, we are more conscious of where the breaks are needed than we would be simply reading it silently from a page. You will of course have used commas while writing the work, but I can guarantee that when you read it aloud, you will start to ask yourself, ‘Is this comma really necessary’ or ‘Would this make more sense if I added a comma here?’  

Should I use a comma before ‘and’?

Commas are naturally used to separate words in a list or sequence. For example, 

The following may not be brought into the exam room: laptops, mobile phones, cameras and notebooks. 

 This sentence follows the convention that a comma is not necessary before ‘and’. However some would claim that a comma should be used here, so the sentence would be:  

The following may not be brought into the exam room: laptops, mobile phones, cameras, and notebooks.   

When a comma is used before ‘and’; it is known as the Oxford or serial comma. Some style guides insist that the Oxford comma should be used, whereas others insist it should not be; therefore, it you are writing an essay, be sure to consult the style guide. The Oxford comma is more commonly used in the United States than it is in the United Kingdom and Australia. However, if you are not required to follow a style sheet then the choice is yours, but you should be consistent. My own point of view is that the Oxford comma is not necessary unless it is needed to clarify the meaning of the sentence. Consider these two sentences, where the Oxford comma is used in Sentence 1. 

1.     On Tuesday I shall be having lunch with two company directors, Sylvia, and George.

This is saying the that writer will be having lunch with four people, and that Sylvia George are not directors. 

2.     On Tuesday I shall be having lunch with two company directors, Sylvia and George.

This is saying that the writer will having lunch with two people, Sylvia and George who are both directors. 

So it can be seen that if the Oxford comma is not used, the meaning is completely changed. 

Commas used in pairs

Commas are often used in pairs to separate a clause from the rest of the sentence. Here are some examples, one from an essay and one from a novel. 

The experiment, which was conducted by six chemistry students, verified the hypothesis. 

A tall lady, who was wearing a red hat, answered the door. 

If the commas in the second example were not used, the meaning could be changed with hilarious results! 

Use of commas with link words

Academic writing frequently uses link words to connect sentences. These usually come at the start of a sentence and are followed by a comma; for example, 

Consequently, the report was translated into English, French and German. 

Commas and semi-colons

Sometimes commas and semi-colons can be confused. Semi-colons are used in longer sentences where too many commas could make the sentence unclear. Also, commas can be used in conjunction with semi-colons when link words are used; for example, 

Only 10 percent of the participants answered the questionnaire; therefore, it was considered to be invalid. 

Use of commas in citations

Each of the various referencing styles has its own requirement for the use of commas in citations; for example, a comma is inserted between the name and the date, (Brown, 2005). Where multiple names are cited, both commas and semi-colons are used, (Brown & Smith, 2010; Williams & Green, 2012). The style guides of the referencing systems should be consulted for more details.

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