Commas separate clauses and phrases in a sentence.
Unlike colons and semi-colons, commas do not always separate grammatically complete clauses. Commas are often described as representing natural pauses in speech and help define meaning by distinguishing between clauses. However, take care with this rule of thumb - commas are frequently used where they are not necessary.
Commas are used to create different kinds of list:
- All they needed to play the game was a bat, a ball, the backyard and a sunny afternoon.
- The Labour party is promising to improve health services, raise performance in schools and pour millions of pounds into public transport.
- It was a bright, sunny, beautiful day.
Note that there is no comma before the 'and' which introduces the final item in these lists. Whether a comma should be used before 'and' in a list is debated, but there are some situations where a comma is needed to avoid ambiguity. For example:
- The police wanted to speak to the company's owners, the secretary, and the finance manager.
Without the comma before 'and', this sentence could be interpreted as meaning the secretary and the finance manager are the company’s owners, rather than additional people the police want to question. Commas are also used to avoid ambiguity or clarify meaning in a number of other situations. Consider how the following would read without a comma:
- As long as he is working, the children will eat;
- It is easier to hurt than love, my mother always says.
A comma is always needed before and when it is being used as a conjunction, i.e. to join two clauses or phrases which could standalone. This is also true of words like but, while, yet and although:
- Some people still support the government, while others say they want them out;
- It was a shame it rained last weekend, but everyone had fun anyway.
- I was happy with the shirt my mum gave me, although I would have preferred a coat, and red is not my favourite colour.
Missing out the conjoining words in such examples is not acceptable in formal written English, even when the sense is obvious from just using a comma. Also avoid the trap of using this construction with words such as however and nevertheless; these start distinct sentences or clauses, and must always follow a full-stop, colon or semicolon.
Commas are used to separate subordinate and relative clauses in sentences:
- I'd heard that the film, which had earned rave reviews, was not very good;
- The worst thing about her, and I don't say this lightly, is that she never took any pride in her work.
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