There are several types of dashes, each with specific uses. For our purposes here, there are three types to know: the em dash, the en dash, and the hyphen. Most document creation programs have em and en dashes available. For those that don't, use two hyphens to represent an em dash, and a hyphen to represent an en dash.

The em dash is the longest and denotes an abrupt change, interruption, or emphatic phrase. Do not place spaces before or after the dashes:

  • The professor's hypothesis—though rejected by scholars—actually had merit.

The en dash is shorter than the em dash and is used to connect continuing or inclusive numbers:

  • 1968–1972
  • 10:00 a.m.–5:00 p.m.
  • pp. 38–45

En dashes should be used in complex adjectival phrases to avoid confusion:

  • the post–Civil War period
  • non–brain-injured patients
  • Winston-Salem–based company
  • physician-lawyer–directed program

The hyphen is used for numbers that are not inclusive, such as Social Security numbers or for hyphenated compound words, names, or modifiers:

  • word-of-mouth, Joseph Gordon-Levitt, a fast-moving car