Colons and Dashes

Simple Rules for Usage [1]

The basic difference between a colon and a dash is that a colon throws the reader's attention forward, whereas the dash throws the reader's attention backward.

Colons

The colon signifies that what follows is a specification of what was formally announced in the clause on the left-hand side of the colon.

  1. A colon must follow a grammatically complete lead-in sentence or independent clause. What falls before the colon must make grammatical sense on its own. Examples:
    Correct Incorrect
    The courses I am taking this semester are as follows: English, sociology, economics, political science, and psychology. The courses I am taking this semester are: English, sociology, economics, political science, and psychology.

    An independent clause precedes the colon.

    There is no independent clause.

  2. A colon may precede a word or phrase, a clause, a series, or a lengthy quotation. Examples:

    Word

    The reaction of the crowd signified only one thing: apathy.

    Clause

    His approach works like this: after displaying his product and extolling its virtues, he asks the housewife if she has a small rug that she would like to have cleaned

    Series

    Examples of the diction used to evoke the horror of the scene include vivid images like these: "coughing like hags," "thick green light," "guttering," "white eyes writhing in his face," "gargling from froth-cupped lungs."

    Lengthy quotation

    Toward the end of the Preface, Dr. Johnson confessed that he abandoned his earlier expectation that his dictionary would be able to "fix the language":

    Those who have been persuaded to think well of my design will require that it should fix our language and put a stop to those alterations which time and chance have hitherto been suffered to make in it without opposition. With this consequence I will confess that I flattered myself for a while; but now begin to fear that I have indulged expectation which neither reason nor experience can justify.

  3. After the colon, quoted sentences regularly begin with a capital letter; however, other independent clauses that follow the colon can begin with either a capital letter or a lower-case letter.
  4. When using the colon to separate two main clauses, the second should explain or amplify the first: a colon can also imply that the second clause is a result of the first.

    Example:

    What falls after the colon can amplify or explain the first clause:

    The American conceives of fishing as more than a sport: it is his personal contest against nature.

  5. The colon is also used in referencing scriptures, between titles and subtitles, and in the salutation of business letters:

    Scripture

    The text of the sermon was Matthew 6:10.

    Title: Subtitle

    I had just read On Being Funny: Woody Allen and Comedy by Eric Lax.

    Business Letter

    Dear Sir or Madam:

Dashes

  1. Word processors create a dash from two hyphens placed between two words, with no spaces. (In handwriting, a dash should be made slightly longer than a hyphen.)
  2. A dash signals a different relationship between the word-groups that precede them and those that follow them. Note the distinction between the two sentences:

    Colon

    Dash

    The reaction of the crowd signified only one thing: apathy.

    The crowd clearly indicated their indifference to the provocative speech—an apathy that later came back to haunt them.

  3. Use a dash to set off an introductory phrase when the word or word-group that follows it constitutes a summation, an amplification, or a reversal of what went before it.

    Examples:

    English, psychology, history, and philosophy—these were the classes I took last quarter.

    If he was pressured, he would become sullen and close-lipped—a reaction that did not endear him to the Senate.

  4. Use a dash to show an abrupt shift in tone, or hesitation in speech.

    Examples:

    Could she—should she even try to—borrow the money?

    "Well, I—uh—I just think there are other ways to look at it."

  5. Use a dash to set off introductory lists and added explanations or illustrations.

    Example:

    Allison, Becky, Robin—those are the advisors working on Sunday.

  6. Use a pair of dashes to add qualifying or rectifying information in abrupt parenthetical elements.

    Using a dash to set off a parenthetical phrase emphasizes the contents of the parenthetical more than using a comma.

    Example:

    In some instances—although no one will admit it—the police overreacted to the problem.

  7. Use the dash cautiously in formal writing. Do not use a dash when a comma, semicolon or period is more appropriate. What about Commas?
    Commas are used to set off the mildest kind of interrupting element—they tend to place less emphasis or importance on the interrupting clause than the dash.

    Example:

    The agency, we have just learned, had previously reported the incident to the Department of Justice.

[1] Compiled from rules and examples found in The Little Rhetoric & Handbook With Readings by Edward P.J. Corbett, Writing Well by Donald Hall, & The Harbrace College Handbook, by John C. Hodges and Mary E. Whitten.