Grammar Monster
Grammar Monster

Using a Colon to Extend a Sentence

The Quick Answer
A colon can be used to introduce some more information about something mentioned earlier in the sentence. For example:
  • He wanted just one thing: revenge.
  • He knew what his wish would be: the ability to turn stones into gold.
A colon is not used to introduce a new idea to a sentence. For example:
  • He wanted just one thing: he wanted it since he was boy.
New ideas are introduced by a new sentence or, if you want a smooth transition between the sentences, a semicolon. For example:
  • He wanted just one thing. He wanted it since he was boy.
  • He wanted just one thing; he wanted it since he was boy.

Using a Colon to Extend a Sentence

You can use a colon to introduce words that offer a more detailed version of something previously mentioned in the sentence.

Examples of Colons Used in Sentences

Here are some examples of colons used correctly and incorrectly in sentences:
  • The cat's fur was found in two rooms: the bedroom and the kitchen.
  • His success is attributed to one thing: determination.
  • It is by the fortune of God that we have three benefits: freedom of speech, freedom of thought, and the wisdom never to use either. (Mark Twain) 
  • He will be the winner of Loughborough's oldest award: the Arthur Scotland Trophy.
  • Ian had caught 3 fish: a perch and 2 gudgeon.
  • Ian had caught 3 fish: this was the first time he had been fishing.
  • (You cannot use a colon to introduce a new idea.)
  • Janice liked to talk: she often exaggerated.
  • (Remember, a colon introduces an idea previously mentioned in the sentence.)
  • Janice liked to talk. She often exaggerated.
  • (A new idea is introduced with a new sentence.)
  • Janice liked to talk; she often exaggerated.
  • (When a slight break is preferable to a new sentence, you can use a semicolon to introduce a new idea, but you cannot use a colon.)
  • I have made an important discovery: alcohol, taken in sufficient quantities, produces all the effects of intoxication. (Oscar Wilde)
  • In this world, there are only two tragedies: one is not getting what one wants, and the other is getting it. (Oscar Wilde)

(Beer mat)

This should be:

"Dot arrived late at Roger's dinner party; she was determined..."

or

"Dot arrived late at Roger's dinner party. She was determined..."

but not

"Dot arrived late at Roger's dinner party: she was determined..."
Beware

Very Occasionally, You Have a Choice between a Semicolon and a Colon

It's not common, but sometimes it is unclear whether the words to the right of the colon are an extension of something to the left or a new idea. Below is an example where either a colon or a semicolon would be acceptable. This doesn't happen too often.
  • No one was seriously hurt in the accident; one man broke his index finger.
  • No one was seriously hurt in the accident: one man broke his index finger.
Read more about extending sentences with colons, dashes, and semicolons.