Colons introduce material that amplifies the preceding statement or elements. The element following the colon begins with a capital letter if it is more than one sentence long, a formal statement, or a quotation.
We found this to be extraordinary: young people are very enthusiastic about our study.
The study revealed an unexpected result: Sleep-deprived people are more effective at driving with their eyes closed. Well-rested people are more cheerful.
Do not place a colon in the middle of a sentence, between the verb and object or between a preposition and object.
Wrong: You will need: your best attitude and a good night’s sleep.
Correct: You will need your best attitude and a good night’s sleep.
Wrong: We will be traveling to: New York, Idaho, and Rhode Island.
Correct: We will be traveling to New York, Idaho, and Rhode Island.
Place a colon after the salutation in a business letter or address or to introduce a list or series:
Dear Alumni and Friends:
Please include the following items in your suitcase: socks, ties, and underwear