Using the comma

Study guide

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This guide explains how the comma (,) can be used to make your writing clear, unambiguous and easy to read. It gives examples of the main uses of the comma, and highlights some commonly encountered problems.

Other Useful Guides: Using the semi-colon and colon, Using the apostrophe.

Why use commas?

Commas are used to divide or separate parts of a sentence in order to make the meaning clear and the sentence easier to read. They mark a brief pause in the sentence, usually at a point where you would naturally pause if you were speaking rather than writing. They may be used to separate individual words or phrases within the sentence. Some examples of the main types of usage are given below.

Using commas to separate items in a list

Commas are used to separate the individual words or phrases that together make up a list.

The fish kept in the ponds were eels, tench, pike, perch and carp.

The main reasons for the closure were low enrolment, poor learning material, staff recruitment problems and inadequate funds.

Note that a comma is not normally used before the last item in the list, unless it is needed for clarification.

The choices were History and Archaeology, Archaeology and Sociology, and Ancient History.

Here, a comma is used before the last item in the list to avoid confusion.

Separating the parts of a sentence

Commas are used to separate an introductory word or phrase from the main sentence, or to separate a word or phrase that briefly interrupts the flow of the sentence. In the examples below, the introductory and interrupting words or phrases have been italicised.

Nevertheless, many critics see value in this theory.

After the first decade, the changes were fully integrated into the system.

Numerous studies, however, prove that the theory is inaccurate.

The same theory, according to most writers, can be applied to language acquisition.

Similarly, commas are used to separate an afterthought or a final phrase that contrasts with the main part of the sentence.

The war was vitally important for Europe, far more than it was for Britain.

To understand a particular culture we must look at the whole of society, not just its individual parts.

A single sentence can, of course, use commas in more than one way. In the following example, commas are used to separate an introductory phrase, punctuate a list and separate a final contrasting phrase.

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To use the comma effectively, avoid overuse as this can make the sentence difficult to read and understand. Use the comma purposefully, as shown in the example above, and re-read a longer sentence to check the pauses are in the most helpful places.

Using commas to link simple sentences

A series of short, simple sentences can be jerky and tedious to read.

The University is large. It is close to the town centre. There are special rooms available. Advance reservation is necessary.

A way of improving the flow of the writing is to link sentences with a comma

together with a linking word (a co-ordinating conjunction) such as and, but,

so, or, nor or yet.

The University is large, and it is close to the town centre. There are special rooms available, but advance reservation is necessary.

Warning!

A comma cannot be used on its own to join two sentences. A comma only indicates a pause in a sentence; it can not join sentences without the addition of a co-ordinating conjunction. For example, these two sentences, whilst grammatically correct, would read better if joined.

The people followed their own creed. They were willing to die for it.

However, they can not be joined by using a comma on its own, as the comma shows only a pause, not a link.

X The people followed their own creed, they were willing to die for it.  X

A comma together with a co-ordinating conjunction joins the sentences correctly.

The people followed their own creed, and they were willing to die for it.

Sentences can sometimes be joined effectively using a semi-colon (;). The companion leaflet, Using the Semi-colon and Colon provides a guide to its use.

Summary

If in doubt about your use of commas, read each sentence aloud, pausing briefly at each comma. If the sentence flows badly and seems jerky, you probably have too many commas. If you are breathless by the time you have reached the end of the sentence, you might need to insert some commas at appropriate points as shown in this guide. It may even be necessary to divide a very long sentence into two or more separate sentences.

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