Skip to main content

2.1 The comma

The comma indicates structural breaks in a sentence. As we saw in the ‘Sentence Structure’ section of The Little Red Writing Book, commas are used:

Similarly, the comma is used:

Commas are also used:

Notice that the comma before the ‘and’ at the end of a list is optional. Be consistent; either use the comma before ‘and’ all the time or not at all.

The advantage of putting a comma before ‘and’ is that it avoids potential ambiguity. For instance, in the following sentence, how many people did the journalist interview?


Did the journalist interview one person (the CEO of Coca-Cola, who is a millionaire and a Harvard graduate) or is it three separate people. It is difficult for the reader to decide. Using a comma before ‘and’ avoids this confusion.

The Comma With ‘Which’ And ‘Who’

When a phrase beginning with ‘which’ or ‘who’ is a support unit providing additional (but non-essential) information about the control unit, it needs to be marked off from the control unit with a pair of commas. In the following examples, the control unit is highlighted in orange. The support units add to the main meaning of the sentence.


Phrases beginning with ‘which’ or ‘who’ can also be an integral part of the subject. If we omit the phrase, we change the main meaning of the sentence. Therefore, we do not in these instances put a comma before ‘which’ or ‘who‘. In the following two examples, the subject is highlighted in green.


In Examples 3 and 4 the word ‘which’ may be replaced by ‘that’; however, it would not be correct to replace ‘which’ with ‘that’ in Example 1 because in Example 1 it is not an integral part of the subject.

Make sure that you don’t accidentally change the intended meaning by inserting a pair of commas. In the following example, the subject of the sentence is in bold letters.



In the first version of the sentence, the subject is ‘students; the sentence implies that all students are drunk and should be expelled. In the second version, the subject is ‘students who are drunk; it is only this particular group of students who should be expelled.



Previous Page Next Page