Using Colons (Grammar and Punctuation)

The Quick Answer

Colons are used:

To extend a sentence to expand on something previously mentioned in the sentence (e.g., I'm looking for just one personal trait: discipline. )
After an introduction (e.g., I've seen the following: ants, a cockroach, and a rat. )
In references, times, and titles (e.g., Read Genesis 1:1 before 07:30. )
With quotations (e.g., He said: "Curiosity killed the cat, but for a while I was a suspect." )

Using Colons

Colons (:) are quite versatile. It is worth learning how to use them — especially how colons allow you to expand on an idea previously mentioned in the sentence. (If you can master this idea, you'll have a useful tool in your writing armoury.)

A Video on Using Colons

Here is a video summarizing this lesson on colons:

Using Colons to Extend a Sentence

Think of a colon (:) as the language version of an equals sign (=) in mathematics. The information on the left of the colon equals the information on the right.

Usually, the information on the right is an expansion of whatever is mentioned on the left. For example:

He blamed his divorce on one thing: beer.
There are two reasons why I don't believe the alibi: there is no visa in his passport, and he is petrified of flying.

Sometimes, the ideas either side of the "equals sign" are a little harder to marry up. For example:

I have made an important discovery: alcohol, taken in sufficient quantities, produces all the effects of intoxication. (Oscar Wilde)

You cannot introduce a new idea with a colon. For example:

I have made an important discovery: it's my first important discovery this year.

Using Colons after Introductions

A colon can be used after an introduction. The wording to the left of the colon will introduce whatever follows on the right. For example:

The Victorian printing set is missing the following characters: Q, R, K, and the question mark.
He voted for the following films:

(1) Jaws
(2) The Princess Bride
(3) Shawshank Redemption

Note: You cannot use a semicolon (;) for this purpose.

Read more about colons for introductions
Read more about using bullet points

Using Colons in References and Times

Colons can be used to divide the parts of references, titles, and times. For example:

I am currently reading "How To Get Your Own Way: Who's Manipulating You?".
Genesis 1:1 starts "In the beginning God created the heavens and the earth."
07:30 - Breakfast
08:30 - Meet at the lake and prepare the kayaks
09:00 - Select teams

Using Colons with Quotation Marks

Colons can be used to introduce quotations. For example:

It's hard to disagree with Frank Zappa, who said: "Art is making something out of nothing and selling it."

In this example, the quotation is introduced with a colon. However, it could have been introduced with a comma or with nothing. There is a useful guideline out there which states that if your quotation is longer than six words (and you're not worried about controlling the flow of text), then use a colon. (Note: This is just a guideline to remove the need to think about what punctuation to use. It's definitely not a strict rule.)

Read more about colons before quotations