I’ve always been quite interested in typography, but one subtlety I’ve never researched is the array of dashes available, nor their correct grammatical uses. This Wikipedia article gives a very detailed explanation, but here’s a shorter version.
Essentially, there are three types:
– the hyphen or minus (-)
– the en dash (–)
– the em dash (—)
(Note that the hyphen and en dash may look similar under small font settings, but they’re actually different symbols.) The hyphen or minus isn’t actually a dash at all. It’s used to hyphenate words or as a mathematical symbol.
The en dash is slightly longer than the hyphen, being half as long as the font is high. So if you’re using twelve point, an en dash is six points in length. (Its name comes from the fact that this is generally the approximate width of the ‘N’ character.) Essentially, it’s used where there is a connection between two things.
– Date and time ranges: June–July, 1–2pm, 3–5 years old
– Page ranges: pp. 38–55
– New York–London flight
– Where two words shouldn’t be hyphenated, but are associated: mother–daughter relationship
– As a hyphen in compound adjectives, where the adjectives don’t refer to one another: pre–World War II, anti–New Zealand
Finally, the em dash is twice as long as the en dash. As such, it’s as long as the font is high. It’s used in the following instances.
– To mark a sudden ‘parenthetical’ break of thought, either at the end of a sentence (in which case you use one) or mid-sentence (where you use two). Here, it could be thought to be replaceable by a colon or parentheses respectively.
– To mark an open date range (Dan Harrison, 1973—)
In North American and old-British usage, the em dash should never be surrounded by spaces in the first example above. Although not officially sanctioned, modern practice is to instead use a spaced en dash, which I prefer. It gives necessary space to the break, allowing the reader to breathe and mentally separate what is to follow from that which has preceded.
Just as with the degree sign (°), it’s a shame that neither of the dashes has made it to the standard keyboard, leaving writers to copy and paste it from somewhere else, or use some difficult-to-remember keyboard shortcut.
Nonetheless, I will strive to use these correctly moving forward.