Colons have two main uses: to introduce a list when the list follows a complete sentence and to introduce an explanation or example, particularly for emphasis. Colons are not used after forms of the verb to be or after prepositions or in sentences that use such as or like to set up a list.
Colons are used to introduce a list when the list follows a complete sentence.
- Susan intended to cut down on her grocery bills by eliminating three luxuries: ice cream, Twinkies, and Perrier.
There is a complete sentence before the list. Colons are not used before lists that are set up with such as or like because these words create an incomplete sentence, and as stated above, you need a complete sentence before a list to use a colon. Use a comma before such as or like.
- She likes the simple things in life, such as diamonds, yachts, and limos.
For the same reason, no colon is used following forms of the verb to be or after prepositions.
- My favorite places are Hawaii, San Diego, and Rome. (“are” is a to be verb and the portion before the underlined portion is not a complete sentence, so no colon)
- I earned As in my English, government and math classes. (“in” is a preposition and the portion before the underlined portion is an incomplete sentence)
Introducing Explanations or Examples
Colons may be used to direct the reader’s attention to an important explanation or add emphasis to the statement. Again, what comes before the colon must be a complete sentence.
- Tom craved only one thing: absolute power.
This statement is a little more forceful than other phrasing:
- Tom craved only absolute power.
Note: this is grammatically correct, but lacks the emphasis of the first example.