Summary of Commas

There are four types of comma: the listing comma, the joining comma, the gapping comma and bracketing commas.
A listing comma can always be replaced by the word and or or:

Vanessa seems to live on eggs, pasta and aubergines.

Vanessa seems to live on eggs and pasta and aubergines.

Choose an article from the Guardian, the Independent or the Times.

Choose an article from the Guardian or the Independent or the Times.

Stanley was an energetic, determined and even ruthless figure.

Stanley was an an energetic and determined and even ruthless figure.

A joining comma must be followed by one of the connecting words and, or, but, yet or while:

The report was due last week, but it hasn't appeared yet.

The motorways in France and Spain are toll roads, while those in Britain are free.

A gapping comma indicates that you have decided not to repeat some words which have already occurred in the sentence:

Jupiter is the largest planet and Pluto, the smallest.

Bracketing commas always come in pairs, unless one of them would come at the beginning or the end of the sentence, and they always set off a weak interruption which could in principle be removed from the sentence:

My father, who hated cricket, always refused to watch me play.

We have a slight problem, to put it mildly.

If you're not sure about your commas, you can check them by using these rules. Ask yourself these questions:

1. Can the comma be replaced by and or or?

2. Is it followed by one of the connecting words and, or, but, yet or while?

3. Does it represent the absence of repetition?

4. Does it form one of a pair of commas setting off an interruption which could be removed from the sentence?

If the answer to all these questions is `no', you have done something wrong. Try these questions on the following example:

The publication of The Hobbit in 1937, marked the beginning of Tolkien's career as a fantasy writer.

Can that comma be replaced by and or or? No — the result would make no sense. Is it followed by a suitable connecting word? No — obviously not. Have some repeated words been left out? No — certainly not. Is it one of a pair? Not obviously, but maybe the interruption comes at the beginning or the end. Can the words before the comma be safely removed? No — what's left is not a sentence. Can the words after the comma be removed? No — the result would still not be a sentence.

We get the answer `no' in every case, and therefore that comma shouldn't be there. Get rid of it:

The publication of The Hobbit in 1937 marked the beginning of Tolkien's career as a fantasy writer.

Try another example:

Josie originally wanted to be a teacher, but after finishing university, she decided to become a lawyer instead.

Let's check the first comma. Can it be replaced by and or or? Certainly not. Is it followed by a suitable connecting word? Yes, it's followed by but. So the first comma looks OK at the moment. Now the second comma. Can it be replaced? No. Is it followed by a connecting word? No. Does it stand for a repetition? No. Is it one of a pair? Possibly — but can we remove the words set off by the pair of commas? Let's try:

Josie originally wanted to be a teacher she decided to become a lawyer instead.

This is clearly wrong. Is there an interruption at the end of the sentence?

Josie originally wanted to be a teacher, but after finishing university.

This is even worse. (It does make sense of a sort, but the wrong sense.) There's something wrong with that second comma. Try getting rid of it:

Josie originally wanted to be a teacher, but after finishing university she decided to become a lawyer instead.

This makes perfect sense, and it obeys all the rules. The comma after teacher is a joining comma, but that second comma was a mistake.

In fact, there's another way of fixing this sentence. The words after finishing university actually make up a weak interruption. So you can, if you prefer, put a pair of bracketing commas around these words:

Josie originally wanted to be a teacher, but, after finishing university, she decided to become a lawyer instead.

Check that this new version is also correct by removing the words set off by the pair of bracketing commas:

Josie originally wanted to be a teacher, but she decided to become a lawyer instead.

This is a good sentence, so the version with three commas is also correct. Remember, you don't have to set off a weak interruption with bracketing commas, as long as the meaning is clear without them, but, if you do use bracketing commas, make sure you use both of them.

In sum, then:

• Use a listing comma in a list where and or or would be possible instead.

• Use a joining comma before and, or, but, yet or while followed by a complete sentence.

• Use a gapping comma to show that words have been omitted instead of repeated.

• Use a pair of bracketing commas to set off a weak interruption.

Finally, commas are used in writing numbers and dates.

Maintained by the Department of Informatics, University of Sussex