A comma makes the different parts of a sentence clearer by telling the reader to take a short pause. Like all punctuation, its function is to eliminate ambiguity and prevent readers from having to read a sentence twice. It is used in three main ways.

To separate items in a list

Situations like this: “We look at four main areas: general insurance, life insurance and pensions, taxation and financial regulation, and investment.” Here, because some items include the word “and”, a comma is needed before the final “and” to make things clear. There is nothing wrong with putting a comma before the word “and” if it makes the sentence more clear.

If you are using several adjectives to describe a noun, separate them with commas: “a profitable, growing, successful company”. Here three adjectives are applied to one noun. But beware of putting in an unnecessary comma in a situation like this: “a profitable, growing limited company”. Here, the noun is “limited company” (in the sense of “limited liability company”) and it is being described by two adjectives. Putting a comma between “growing” and “limited” would imply that the company is limited in some more damning way than in its liabilities.

To separate major pieces of a sentence

No one likes to read lots of very short sentences in succession, so why not link two together by using a comma followed by “so”, “but” or “and”? For example: “We help companies to improve their writing, and we begin by making sure they know what they want to achieve.”

NOTE: Do not link separate sentences solely with a comma: “Don’t just go straight for the cheapest, choose a computer that will last around five years.” Here the comma should be replaced with a semicolon or a dash.

To separate out extra detail

We often want to give the reader extra information, a comment or an aside. This has to be marked out with commas at the beginning and end:

Taylor-made, in partnership with Acme Ltd, is working on a major new history of mousetraps.

Here “in partnership with Acme Ltd” is a bit of extra information – if you remove it the sentence still makes sense. However, you must be careful to put both commas in – otherwise readers can get very confused. Commas are often used this way to show someone’s position: “Robert Taylor, our managing director, said…” The phrase between the commas is sometimes called a “sentence interrupter”. Common ones are “for example”, “however” and “such as …”. They can, when used sparingly, add variety and interest to your writing.



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