The colon is a punctuation mark that serves multiple functions. Here are five common uses of the colon:
1. To introduce a list, speech, or quotation
The witches’ potion contains hideous ingredients: bats’ eyes, bogies, fangs, and unicorn blood.
Speaking at Shane’s funeral, Stephen addresses the crowd: “Family, friends, guests….”
Timothy Smith has argued about the importance of self-empowerment: “We must be brave enough to face that which frightens us.’
2. To express a contrast
God is good: The Devil is evil.
Hot weather is lovely: cold weather is awful.
Friends are good: foes are bad.
3. To make a pointed connection
Emily joined the Police Force: her father was a copper.
Nigel knew he was going to fail his driving test: his enemy’s grandfather was his examiner.
Andrea was arrested and imprisoned for possession: her father was a drug addict.
4. To introduce a concluding clause or climax
After considering the options before her, she came to a decision: she joined the circus.
Timothy could take his father’s negative criticism no longer: he packed his bags and moved out.
After struggling to choose between a red car and a yellow motorbike, he called the company: he placed an order for the red car.
5. To add emphasis to an idea
Consider the following sentences:
a. The one thing humanity cannot live without is love.
b. There is one thing that humanity cannot live without: love.
Both of these sentences are grammatically correct, but the second is more persuasive, as the colon adds emphasis to the statement. (You might also recognize the second sentence as a cleft sentence).
Notes
1. In British usage, a colon is not usually followed by a capital letter, unlike in American usage, which prefers to use a capital.
2. It is important to note that colon construction may, on occasion, be inverted, with a list preceding a general summary or statement:
Charles Dickens, William Shakespeare, J.K. Rowling: all three have contributed to English literature.
3. Do not use a colon when a list is incorporated into the flow of a sentence.
Correct: The music store specializes in glam rock, punk and heavy metal.
Incorrect: The music store specializes in: glam rock, punk and heavy metal.
Conclusion
Colons are powerful pieces of punctuation when used properly, as they aid word flow and add weight to statements and arguments, but they should be used with care.