I am fond of dashes. It’s possible that I am addicted to them. Fifty years ago, a graduate professor tried an intervention with me, but he was not entirely successful. I do hope I use them more judiciously than I once did.
I think I like them because they give me an opportunity to interrupt myself—which is something I do frequently when I talk—before moving on with the sentence. I could have used parentheses to accomplish the same purpose. Separating a word or phrase from the rest of the sentence using dashes is supposed to emphasize the parenthetical phrase; using parentheses is meant to de-emphasize the parenthetical word or phrase.
Below is another example of the use of dashes to set off an expression:
Many marks of punctuation are in decline, and I mourn some of them. One of my very favorite marks of punctuation—the semicolon—is probably headed for extinction.
I do see people insert dashes into text occasionally, but as often as not, they are formatted incorrectly. The proper way to format a dash (and the method I used to key the example above) is to key the word punctuation and immediately follow the last n in the word punctuation by striking the hyphen key twice, followed immediately by the word is, without striking the space bar anywhere in this sequence. In most word processing applications and text editors, what happens is that the two hyphens automatically turn into something called an em dash, which is a one continuous line that is longer than a single hyphen.
An em dash is the width of a capital M in whatever font you are using.
I know that grammar and punctuation are both increasingly defined as descriptive rather than prescriptive, but please do not use a single stroke of the hyphen key to represent a dash. It looks sad. Worse than that, I think, is the practice of allowing the single stroke of the hyphen key to be flush against only one of the two words on either side of it.
The following is an example of what I am talking about. Please remember that this is a negative example. Do not use the hyphen key in the following way:
Many marks of punctuation are in decline, and I mourn some of them. One of my very favorite marks of punctuation -the semicolon- is probably headed for extinction.
I hope you can see the awkwardness of the formatting above, in contrast to the elegance of the first version.
Hyphens (a single stroke of the hyphen key) are used in expressions such as the following:
an off-the-beaten-path strategy
a low-key approach
a business-friendly solution
Notice the absence of any white space between the hyphen stroke and the text on either side of it.
There is also something called an en dash, which is not as short as a hyphen but not as long as an em dash. However, not every word processing program or text editor gives you the option of creating it. But when I have the option, I often use an en dash to indicate a number range: “The dates of the conference are July 27 - 30.”