Em Dashes Exercise (22)

All but one of the following sentences demonstrate incorrect style for use of em dashes; revise sentences as necessary:

Answers and Explanations

Em dashes are used singly, to signal an interruption at the end of a sentence or to indicate a break in thought that continues to the end of a sentence, or in pairs, to indicate parenthesis (when a pair of commas or parentheses might also be appropriate).

1.
Original: The following streets will be blocked off -- Alder, Elm, and Maple.
Correct : The following streets will be blocked off: Alder, Elm, and Maple.

A colon, not an em dash, is appropriate for introducing a list.

2.
Original: Primates traditionally included simians -- apes and monkeys, for example -- and prosimians -- lorises and tarsiers, for example.
Correct : Primates traditionally included simians (apes and monkeys, for example) and prosimians (lorises and tarsiers, for example).

Using more than two em dashes in a single sentence creates confusion. To set off more than one word or phrase from the main sentence, use parentheses instead.

3.
Original: "I assure you, I would never--," Jones began to protest before Smith cut him off.
Correct : "I assure you, I would never--" Jones began to protest before Smith cut him off.

An em dash used to indicate interruption at the end of a sentence replaces terminal punctuation or a comma preceding an attribution.

4.
Original: They were astonished -- they had never expected to see him again -- and they rushed to greet him.
Correct : They were astonished -- they had never expected to see him again -- and they rushed to greet him.

This sentence shows correct parenthetical use of em dashes.

5.
Original: The primary colors, which can be combined to create intermediate colors -- blue, green, and red -- are based on humans’ trichromatic vision.
Correct : The primary colors -- blue, green, and red -- which can be combined to create intermediate colors, are based on humans’ trichromatic vision.

When em dashes are used parenthetically, the word or phrases set off in em dashes should immediately follow the referent word or phrase, not a subsequent modifying word or phrase.

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