Colons

Posted on 9 January 2015 by Lucy Gregory

 

How to use a colon

The important rule to remember when using colons is that the wording before the colon, must form a complete sentence. If it’s only a phrase or a sentence fragment, then you can’t use a colon. (There are a couple of exceptions to this rule, which I discuss in more detail below.)

Correct use of colon
We discuss four key risks: (1) sustainability of the business model, (2) stability of the core business, (3) management focus, and (4) competition.

Wrong use of colon
Key risks include: (1) sustainability of the business model, (2) stability of the core business, (3) management focus, and (4) competition.

In the second example, the wording before the colon doesn’t constitute a complete sentence, which means the colon doesn’t work. You can either remove the colon or add the words ‘the following’. This does the job of completing the sentence and making the colon work.

Correct use of colon
Key business risks include the following: (1) sustainability of the business model, (2) stability of the core business, (3) management focus, and (4) competition.

 

Introducing a list

There are two types of lists you can write: lists that flow normally in your text and vertical lists (eg bullet or numbered lists).

If you use a colon for a list that flows normally in your text, remember to follow the rule above and make sure the words before the colon form a complete sentence.
 

Correct use
 
I asked Jane to bring three items to the meeting: the agenda, the team’s latest report and biscuits.
 
The property has the following attributes: excellent transport links, high footfall and secure income.
Wrong use
 
I asked Jane to bring: the agenda, the team’s latest report and biscuits.
 
 
The property has: excellent transport links, high footfall and secure income.

 
 
 
Some people follow the complete sentence rule when writing vertical lists (such as bullet lists) as well. However, there’s more flexibility here and it’s common to see vertical lists introduced with a colon where the introductory wording is a phrase or sentence fragment. For more on this, read our post Punctuating bullet lists.
 

Emphasising or clarifying an idea

You can use a colon to give the reader more detail about the idea that came before or to clarify your point. You can’t use a colon to introduce a new idea.

Examples of correct colon use

Sam knew there was only one way to survive the day: a lot of caffeine.

There are only two rules for being successful: one, work out what you want to do, and two, do it. (Mario Cuomo)

I’d like to introduce our two new board members: Tony and Angela.

Harry’s research revealed an important finding: his client is a crook!

An easy way to test your colon is by replacing it with the word ‘namely’*. If the sentence still makes sense, your colon is probably correct.
 

Introducing quoted material or direct speech

There is no definitive rule for choosing whether to use a colon or a comma or nothing at all. I think the easiest practice is to follow the complete sentence rule above. So if the words before the quote constitute a complete sentence, use a colon. Otherwise, go with a comma.

With colon
The Department for Education is responsible for education and children’s services in England: ‘We work to achieve a highly educated society…’

With comma
The Department for Education issued a statement saying, ‘We work to achieve a highly educated society…’

If you have a long quote, you might want to set it apart from the main text as a new and indented paragraph. If you do this, introduce the quote with a colon.
 

Separating parts of a heading, title, reference or contact detail

This is another occasion when you don’t need to follow the complete sentence rule.

Examples of correct colon use

Table 3.2: Average age of European citizens, 2014

Market research survey: how good is your grammar?

How to use hyphens: part 1

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Contact us: 020 3282 7872

 

Capital letter after a colon?

In British English, the word after a colon should start with a lowercase letter unless the word has a capital letter for other reasons (for example, you’re writing a proper name).

You might also want to capitalise the start of a subheading. This is personal preference, but make sure your use is consistent with your organisation’s house style and within the document.
 

Should you put a dash after a colon?

In a word, no.

You might see a colon written like this :– but it’s wrong. There’s no such punctuation mark, and it has no meaning.
 
 
 
*I credit Grammar Girl Mignon Fogarty with this tip.