The Colon

The colon represents a screeching halt in the sentence at which you could substitute words like "that is to say."

  • Usually, it introduces a list.

Students cited three things they liked most about Union: the small classes, the opportunity to get to know their professors, and the beautiful campus.

The colon should not be used every time you introduce a list.  In particular, it should not be used after the verb "to be."  The following is incorrect: The eight parts of speech are: nouns, pronouns, verbs, prepositions, conjunctions, adjectives, adverbs, and interjections.

  • Sometimes, it introduces an expansion or clarification of a point just made. 

She made her point forcefully: students should not be required to pay library fines before graduating.

Notice that this use resembles the use of a semicolon to join two closely related sentences when no conjunction is used.  The distinction is not always clear, but if you can't substitute the words "that is to say," don't use a colon.

The colon has certain other specific uses, including

  • after the salutation in a formal letter.  
    Dear Mrs. Rivera:
  • between the title and subtitle
    Style: Ten Lessons in Clarity and Grace
  • in expressions of time
    12:15 P.M.
  • to introduce a quotation (although commas or no punctuation at all is also common).
    The valedictorian ended his speech with these words:  " We are entrusted with the future.  Let us not betray that trust." 
  • between volume and page number, or chapter and verse.
    College English, 32: 221.
  • in ratios.
    Dilute the chemical 3:1.

Spacing after a colon.

Use one space after a colon (and a period).  Rules change.