The hyphen, the em dash, and the en dash are all horizontal marks of varying lengths. Each functions quite differently from the others. Below are definitions of each, explanations for when to use them, and instructions for typing them on both PCs and Macs.
The hyphen is the shortest of the three and is used most commonly to combine words (making compounds such as “well-being” and “advanced-level,” for example) and to separate numbers that are not inclusive (phone numbers and Social Security numbers, for example).
On computer keyboards, the hyphen appears on the bottom half of the key located on the top row between the “0” and the equals mark (=).
Most people use the hyphen when they need a minus sign in mathematical equations. Some argue that the actual minus sign sits lower than the hyphen, but at least in Microsoft Word, inserting the mathematical minus sign from the symbols list renders the same mark as using the hyphen on the keyboard.
In many instances, correct hyphenation can be a complicated issue. Elsewhere on this site, we discuss the use of hyphens to create compound words and hyphenated adjectives. Here, however, our focus is on the two kinds of dashes.
The em dash is the mark most of us picture when we hear the term dash. It is significantly longer than the hyphen.
We use the em dash to create a strong break in the structure of a sentence. Dashes can be used in pairs like parentheses—that is, to enclose a word, or a phrase, or a clause (as we’ve done here)—or they can be used alone to detach one end of a sentence from the main body.
Dashes are particularly useful in a sentence that is long and complex or in one that contains a number of commas, as in this example:
When we confuse the em dash with the hyphen, we make a sentence virtually impossible to read. If we had used a hyphen in place of each dash two sentences ago, it would seem as though we had hyphenated two pairs of words in the sentence: “parentheses-that” and “clause-or,” neither of which makes any sense.
A good rule of thumb is to reserve em dashes for those places where the comma simply doesn’t provide a strong enough break. If a comma (or a pair of them) works, use it.
Parentheses tend to downplay an idea; they suggest that the information in them is helpful but not necessary. Em dashes draw attention to the information they enclose or set apart. Typically the writer is telling the reader that the information being set off by em dashes is important.
The en dash is slightly longer than the hyphen but not as long as the em dash. (It is, in fact, the width of a typesetter’s letter “N,” whereas the em dash is the width of the letter “M”—thus their names.) The en dash means, quite simply, “through.” We use it most commonly to indicate inclusive dates and numbers: July 9–August 17; pp. 37–59.
Many people were not even aware of the distinction between the en dash and the em dash until the advent of word processors, when software programs enabled us to use marks of punctuation that once had been available only to professional printers.
When using the hyphen, the en dash, or the em dash, most style books advocate putting space neither before nor after them. One exception is, of course, when the hyphen is used as a minus sign. The other exception is with a hanging hyphen (see, for example, the word “nineteenth” in the phrase “nineteenth- and twentieth-century literature”). By definition, a hanging hyphen will have a space after it but not before it.
Computer keyboards lack individual keys for either of the dashes. (The symbol above the hyphen is an underline, not a dash.) Before word processing, we had to make do by typing two hyphens. Now we have options.
Note that not all keyboards around the world are the same. We have heard from our readers in countries outside the U.S. that the following shortcuts don’t apply to their keyboards. That said, here are guidelines for typing on many keyboards:
British/Canadian style guides seem wildly inconsistent on the issue of the em and en dash. Some say to use the en dash instead of the em dash, while others go so far as to advocate using the hyphen, advice that would lead to confusion, as we have noted above. Our British and Canadian readers—and, indeed, any English-speaking reader outside the U.S.—should consult the style manual to which they default.
The esteemed Oxford University Press style guide explains how to use both the em and en dashes, so we can assume that at least this authoritative source advocates using both.
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