Some style guides recommend using en dashes in place of hyphens for a wide variety of uses, but The Chicago Manual of Style, the guidebook of record for most American publishing companies, advises a more limited set of applications. According to Chicago style, these sentences would all be written with hyphens, not en dashes:
“He had long flown the San Francisco-Los Angeles run.”
“In 1930, the Smoot-Hawley Tariff Act went into effect.”
“The final score was 6-5.”
“After discussion, the board voted 6-3 to approve the project.”
“Their father-son rivalry persisted for many years.”
“The Michelson-Morley experiment was a significant milestone on the way to the theory of special relativity.”
What, then, are en dashes for? First, they separate two numbers in a number range (as in the inclusive page numbers in a chapter, or the years of birth and death in a person’s life span). Second, the en dash functions as a superhyphen. It is this second function that this post details.
In a simple phrasal adjective, two single words that, as a temporary compound, modify a noun are often hyphenated: “Her high-handed gesture backfired.” (The hyphen’s function is to eliminate ambiguity, so that the sentence is not understood as referring to a handed gesture that is high.)
But when the first of the two terms in the temporary compound is itself a compound, the greater suspensive strength of the en dash is employed, as in “She wears jam jar–bottom glasses” or “The character’s origins go all the way back to the golden egg–laying magic goose.”
Alternately, these sentences can be styled with hyphens between the three words in each phrasal adjective, as in “She wears jam-jar-bottom glasses” and “The character’s origins go all the way back to the golden-egg-laying magic goose.” This style is used when en dashes are discouraged or not an option, such as online (on Web sites, en dashes, unlike hyphens, require use of a code) or in newspapers, most of which do not use the longer symbol. However, such use of hyphenation does not demonstrate the subtle relationship between the elements of the phrasal adjective.
In addition to linking an open compound to another adjective, an en dash serves to connect a proper noun to a word that indicates resemblance or another relationship:
“The character is part Clint Eastwood–type cowboy.”
“You can see him as a Leonardo da Vinci–like genius.”
“She evolved from being a slick Mata Hari–esque female to a more rounded, tomboyish figure.”
This structure clarifies that type refers, for example, to “Clint Eastwood,” not to “Eastwood” alone.
En dashes connect the concepts in the following phrases: “Academy Award–winning actor,” pre–Industrial Revolution technology,” “ex–vice president,” and “non–United Nations action.” However, when connecting a term to a hyphenated compound, a simple hyphen is used, as in “non-English-speaking visitors” or “non-government-sponsored programs.” Another case in which a hyphen, not an en dash, is employed is “post-9/11,” because the short form of the month-date designation is not considered a compound.