Dash
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A dash is a mark of separation stronger than a comma, less formal than a colon, and more relaxed than parentheses. [Elements of Style, Strunk and White]
Dashes should only be used where the use of a more standard form of punctuation (for example, commas) would be inadequate - that is, would not provide the same impact or emphasis.
Note that a dash is not the same as a hyphen, and may be either an em dash or an en dash - both of which have slightly different purposes, as explained below.
The following table shows the differences between the three types of dashes, and gives their HTML character codes:
| Character | HTML Code | Display |
|---|---|---|
| Em dash | — | — |
| En dash | – | – |
| Hyphen | - | - |
Em dash
An em dash should be used to introduce a new clause that represents a sudden change in thought or tone, or to place additional emphasis on a clause. There is no space between the em dash and the preceeding and following words.
Example
| The number of blocked invoices has decreased again this month—to the lowest level in six months! |
Em dashes can, in theory, also be used in place of parentheses. However, given the convention of having no spaces between the dash and the words either side of it, this just doesn't look right and so an en dash (which does have spaces between the dash and the words) is a better choice.
En dash
An en dash should be used in the following cases:
- To identify a parenthetical clause. Here, the em dash is used as an alternative to actual parentheses).
- To indicate a range of numbers, or a relationship between two objects. This is the most common use of an em-dash.
- To separate a prefix or suffix from a two-or more word noun (or verb). This is sometimes known as a compound adjective hyphen, and is used in place of a regular hyphen, to indicate that the prefix or suffix applies to more words than just the word it is attached to (by way of the em dash). See also comments under Hyphen.
Examples of each of these cases are shown below.
Examples
| Parenthetical clause | Employees should avoid taking vacation – unless approved in advance by their manager – during this period. (Note that, unlike the em dash, there are spaces either side of the en dash [only] when used for this purpose.) |
|---|---|
| Number range or relationship | For more information on this topic, refer to pages 17–19 of this manual. These servers have a master–slave relationship. |
| Compound adjective hyphen | This was standard practice in pre–Industrial Revolution Britain. The collection includes a number of Civil War–era muskets. |
