In this edition of “Notes from the Proofreader” we’ll touch on the different types of dashes and their unique roles.
Hyphens are the shortest of the dashes. They are often used to hold together compound or phrasal adjectives that precede a noun to provide clarity, aid in comprehension, and prevent misreading. For example, a heavy metal detector without a hyphen could be interpreted as a metal detector that weighs a lot, whereas a heavy-metal detector with a hyphen is clearly a device that detects heavy metals. Hyphens are also used to hold together some noun phrases (like jack-in-the-box or mother-in-law). And though words formed with prefixes are usually closed up, there are some circumstances where the hyphen is necessary. The Chicago Manual of Style, section 7.85, has a handy chart that explains when to use hyphens with prefixes and in compounds and phrases.
In addition to combining elements, hyphens can also be used to divide elements. For example, they can serve to separate groupings of numerals in phone numbers or Social Security numbers, as well as individual letters when you spell out a word letter by letter in dialogue (CMOS 6.77).
En dash –
En dashes are the midsize dashes—longer than hyphens, but shorter than em dashes. CMOS 6.78 explains that en dashes can be used in ranges, in scores, and to indicate directions. Here are a few examples:
But please do not use the en dash when you’ve introduced the connected elements with either from or between. In those cases the correct constructions are from X to Y and between X and Y.
There are also special circumstances in which en dashes can function just like a hyphen in a compound adjective. This happens when part of a compound adjective is an open compound or if both halves of a compound are themselves hyphenated (CMOS 6.80). For example, New York–style cheesecake or quasi-judicial–quasi-legislative entity.
Em dash —
Em dashes are the longest of the dashes. If you take a look at CMOS 6.81–6.84, you’ll see that a single em dash can be used to indicate a sudden break, to set off a noun from its definition, or to replace a colon (the em dash being less stuffy than a colon). And if you want to make a parenthetical element really stand out, a pair of em dashes can be used as an alternative to commas or parentheses. Make sure to avoid using more than two em dashes per sentence though, because this can create confusion as to what exactly is being set off.
Depending on the style guide you’re following, em dashes can be open (a single space on either side) or closed (no spaces). CMOS advocates for the closed style.
Note: You won’t find a key for the en dash or the em dash on a standard keyboard. But you can easily create them on a Mac by typing option+hyphen for a en dash and option+shift+hyphen for an em dash. If you’re on a PC, this site offers some easy ways to create them. And if you’re working in Google Docs, there’s the option of inserting them as special characters—select “Special characters…” from the Insert menu, and then search for U+2013 to find the en dash and U+2014 to find the em dash.