A dash is a horizontal line that shows a pause or break in meaning, or that represents missing words or letters. Note that dashes are rather informal and should be used carefully in writing. Dashes are often used informally instead of commas, colons and brackets. A dash may or may not have a space on either side of it.
Do not confuse a dash (—) with a hyphen (-), which is shorter.
1. Use a dash to show a pause or break in meaning in the middle of a sentence:
- My brothers—Richard and John—are visiting Hanoi. (Could use commas.)
- In the 15th century—when of course nobody had electricity—water was often pumped by hand. (Could use brackets.)
2. Use a dash to show an afterthought:
- The 1st World War was supposed to be the world's last war—the war to end war.
- I attached the photo to my email—at least I hope I did!
3. Use a dash like a colon to introduce a list:
- There are three places I'll never forget—Paris, Bangkok and Hanoi.
- Don't forget to buy some food—eggs, bread, tuna and cheese.
4. Use a dash to show that letters or words are missing:
- They are really f––––d up. (Typically used for offensive words.)
- I will look ––––– the children. (Typically used in "missing word" questions.)
In fact, there are two kinds of dash:
- the en-dash (–), which is the width of the letter "n"
- and the em-dash (—), which is the width of the letter "m"
However, the difference between them is rather technical and mainly of value to typographers. The dash is a convenient and easy mark to use in hand-writing. But it is often difficult to find on a keyboard and for this reason some people use the easier-to-find but shorter hyphen (-) when word-processing.