One of the finer points of punctuation is the use of dashes. In casual writing, we often use them willy-nilly, but when you are writing nonfiction for publication, take care to use them properly.
Fiction writers only need concern themselves with one kind of dash. They will rarely have use for the other. But nonfiction writers need to understand the differences and when to use them.
The first and most common dash is the em dash—so called because in a proportional font it’s about the same width as the letter M. There’s one in the previous sentence. The em dash is used in nonfiction much as it is in fiction: for an abrupt break that’s not suitable for other punctuation.
I often see writers using semicolons to separate clauses in a sentence like the one at the beginning of the previous sentence. But when the second part of the sentence (the part after the dash above) is not a complete sentence, a semicolon is inappropriate. In other words, if you use a semicolon in a sentence, the parts before and after it should be independent clauses—that is, they could stand as complete sentences if you used a period instead. The use of a semicolon instead of a period shows that they are closely related. If they are not, use a dash.
She worked hard all day; there was a lot to do. [Correct]
She worked hard all day; so much to do. [Incorrect]
She worked hard all day—so much to do. [Correct]
Another use for an em dash is in place of parentheses. When you insert into the middle of a sentence—like this—a phrase that is not grammatically necessary to the sentence, you can enclose it in em dashes. This is seen as less formal than parentheses. Which you choose will depend on your audience. If you are writing for the scholarly market, parentheses are unobjectionable and often preferred. But if you are writing for the general market, parentheses can look stuffy.
Some editors feel em dashes are too casual for formal prose, so be judicious in your use of them if you are seeking traditional publication.
When typing your dashes, leave no space on either side, unless you are writing for a publication that uses the Associated Press Stylebook.
The Other Dash
Less often used is the en dash, which you may guess is so called because it is the width of the letter N. Its primary use is in ranges, such as historical dates and page number citations.
He fought in the 1914–18 war.
The information is on pages 78–81.
The apostle Paul cites the marks of a Christian in Romans 12:9–21
As Chicago puts it, you would use the en dash where you might also use the word to.
A less common use is to form a compound adjective when one of the parts of the compound is a set phrase.
Let me explain. Normally, to form a compound modifier, we hyphenate the parts of the compound, such as in war-torn years (war + torn form a compound adjective modifying the noun years). But if part of the compound is a set phrase, as in Chicago’s example, the post–World War II years (CMOS 6.80), the en dash serves as a sort of superhyphen to bring the whole modifier together.
Well, now the topic has drifted into hyphenation, which is a whole other topic. Next time, friends.
Typing special characters
Nonbreaking space in Word for Windows: ctrl + shift + spacebar
Ellipsis character in Word for Windows: alt + ctrl + period
Em dash in Word for Windows: ctrl + alt + minus key (on the numeric keypad)
En dash in Word for Windows: ctrl + minus key (on the numeric keypad)
Nonbreaking space in Word for Mac: option + spacebar
Ellipsis character in Word for Mac: option + semicolon
Em dash in Word for Mac: option + shift + hyphen
En dash in Word for Mac: option + hyphen