A dash is a little horizontal line that floats in the middle of a line of text (not at the bottom: that’s an underscore). It’s longer than a hyphen and is commonly used to indicate a range or a pause. Dashes are used to separate groups of words, not to separate parts of words like a hyphen does. (learn more about the difference between a dash and a hyphen here). There are three forms of dashes: em, en, and the double hyphen.
The most common types of dashes are the en dash (–) and the em dash (—). A good way to remember the difference between these two dashes is to visualize the en dash as the length of the letter N and the em dash as the length of the letter M. These dashes not only differ in length; they also serve different functions within a sentence.
Em dashes save the day when other punctuation would be awkward. For instance, em dashes can replace parentheses at the end of a sentence or when multiple commas appear in a parenthetical phrase.
Colons enable a writer to introduce a clause that amplifies whatever came before the colon. They are more formal than dashes. However, em dashes are more emphatic than colons. When you want to generate strong emotion in your writing or create a more casual tone, use em dashes. Compare these sentences:
Writers and transcriptionists replace unknown, censored, or intentionally omitted letters with em dashes. In these cases, em dashes appear in pairs or threesomes.
Recall that en dashes are slightly shorter in length than em dashes. En dashes may look similar to em dashes, but they function in a much different way.
Using the En Dash to Indicate Spans of Time or Ranges of Numbers
The en dash is often used to indicate spans of time or ranges of numbers. In this context, the dash should be interpreted as meaning either “to” or “through.” Consider the examples below:
Using the En Dash to Denote a Connection
The en dash may also be used to indicate a connection between two words. Use an en dash when you need to connect terms that are already hyphenated or when you are using a two-word phrase as a modifier. When the dash is used in this way, it creates a compound adjective. See the following examples: