Colons (:) signal to the reader that additional information with follow to elaborate on or to explain a statement. Colons are also used to introduce lists, tables, words, and formal quotations and to show time and ratios.

Rules for using colons

  1. Use a colon to elaborate
    Use a colon after a complete statement if you go further and elaborate on or explain the statement. The information that follows the colon may or may not be a complete statement. If the information that follows the colon is a complete statement, begin the statement with a capital letter
    • Using this program is simple: Open the book and begin.
    • The best part of the week has begun: the weekend.
    • The presidential candidate only spoke about one thing: climate change. 
  2. Use a colon for lists
    Use a colon after a complete statement that introduces a numbered or unnumbered horizontal list.
    • We saw several cars: a Honda, a Ford, and a Toyota. 
    • We saw several cars: (a) a Ford, (b) a Chrysler, and (c) a Honda.
    DO NOT use a colon if the complete statement is followed by a transitional word or phrase such as “namely”, “for example”, “for instance”, or “however”. In this case, use a semicolon (;) before the transitional word and a comma (,) after it.
    • I really liked your initial argument; however, you neglected one major point.
    • We have discussed two options; namely, (1) printing or (2) photocopying..
  3. Use a colon for lists (cont.)
    Use a colon after a statement that introduces a horizontal or vertical list and includes the words “the following”, “as follows”, “these”, or “thus”.
    • We saw the following cars: a BMW, a Jaguar, and a Porsche.
    • Our agenda items are as follows: reading of the minutes, old business, and new business.
    DO NOT use a colon if a horizontal list is introduced by an incomplete sentence. In this case, items in the list complete the sentence.
    • Processing the order requires (1) recording the stock numbers, (2) printing the packing.
  4. Use a colon after a complete statement that introduces a numbered, unnumbered, or bulleted vertical list.
    • You should know these rules:
      • The deadline for applications is July 1.
      • Handwritten applications will not be accepted.
  5. Use a colon when quoting
    Use a colon to introduce a long quotation. Capitalize the first word of the quotation.
    • In her speech, she said: "Success can be measured in many ways. I believe success is finding what you love and making it your life's work."
  6. Other uses for a colon
    • Between hours and minutes in time: 12:30
    • To substitute for the word to in a ratio: 5:1
    • After business letter salutations: Dear Mr. Adams:
    • To separate certain information in citations at the end of a research paper: Diaz–Rico, L. T. (2008). A course for teaching English learners. Boston, MA: Pearson.