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.

What are em dashes?

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.

• After a split second of hesitation, the second baseman leaped for the ball (or, rather, limped for it).
• After a split second of hesitation, the second baseman leaped for the ball—or, rather, limped for it.

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:

• He is afraid of two things: spiders and senior prom.
• He is afraid of two things—spiders and senior prom.

Writers and transcriptionists replace unknown, censored, or intentionally omitted letters with em dashes. In these cases, em dashes appear in pairs or threesomes.

• A former employee of the accused company, ———, offered a statement off the record.
• “H—— are all the same. They cause trouble wherever they go.”
• Carved into the dresser drawer was a faded inscription: “Made for Kristina, by your de——ted sailor.”

What are en dashes?

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:

• The teacher assigned pages 101–181 for tonight’s reading material.
• The scheduled window for the cable installation is 1:00–3:00 pm.
• The 2015–2016 fiscal year was the most profitable year for the new business.

Using the en dash to indicate 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:

• The pro-choice–pro-life argument is always a heated one.
• The Nobel Prize-winning author will be reading from her book at the library tonight.