There are three types of dashes in using the English language writing convention. They are:
- Hyphen
- en dash
- em dash
I have arranged them according to their length, with the hyphen being the shortest and the em dash the longest. Traditionally, and especially when the typewriter reigned, the hyphen is just very short, the length of the en dash corresponds to the length of space the capital letter N will cover while the em dash’s length is as long as the space, you guessed it, that the capital letter M would cover.
When to Use Each
Hyphens are used to structure compound words and to separate non-inclusive numbers. Word combinations such as non-inclusive, self-esteem, mother-in-law are joined with hyphens to make meaning clearer in written communication. They are used to separate non-inclusive numbers such as phone numbers. An example is when you want to give your mobile phone number to someone who lives outside Nigeria, you have to put the international dialling code first, so you write 234(hyphen)8035675587. Some people observe the full division and present their numbers as 234(hyphen)803(hyphen)567(hyphen)5587; that is, 234-803-567-5587.
En dashes are used to represent the word “through”. They more or less indicate a number or date range. For example, if I say, “Alex, please bring in contestants 6-15,” this means I’m expecting nine contestants. And August 2-3 means our training will occur over the two days in the range.
Em dashes are used to indicate a sharp break in speech, especially in a long sentence that already has a few commas and in which the speaker has added another information. For example, “Lagos is the centre of excellence, it is profitable ground for those who are ready to work hard—boy, you WILL work hard for every naira you make—and are ready to give as much as they receive. You have to love Lagos for its promises even if you hate it for making you love it so much.”
Basically, the em dash reduces readers’ confusion or the chances of their getting lost in a winding sentence.
You can use dashes in pairs—like parentheses—or you can use just one towards the end of a sentence—to attach a phrase. (Did you see what I did there?)
One rule applies to all the three dashes, do not put space before or after them. Except for hanging hyphens (I know, I know, take this example first: fifteenth- and sixteenth-birthday)