Dashes can be used to set off material in the midst of a sentence. However, one should try to avoid using them at all. When choosing between dashes and other forms of punctuation (such as commas and parentheses), dashes should be used sparingly and primarily when the material deserves special emphasis. By contract, parenthetical ideas may be lost. In typing or word processing, a dash is formed by placing one space before and one space after two consecutive hyphens. (来源：英语杂志 http://www.EnglishCN.com)

　　破折号使用在词与词中间用以隔开句子成分。然而，我们应尽量避免使用破折号。当在句中需要强调某成分时，在破折号与其他标点符号（如逗号，括号）之间我们应优先并谨慎使用破折号。如省略破折号则可能导致插入部分的语意丢失。在打印或用WORD进行文字系统操作时，应连续打印两个连接符并在其前后分别空一格。

　　Incorrect错误使用: The judge knew the defendant——she had been his third wife——and he therefore recused himself.

　　Correct正确使用: The judge knew the defendant —— she had been his third wife —— and he therefore recused himself.