The dash has uses similar to those of the comma．However，it indicates more abruptness and is used for clarity when commas have already been used．The dash can also set off parenthetical expressions to make them more emphatic．

破折号的作用类似于逗号，表语意的停顿，但往往强调思想的突然中断和语气的突然改变。有时也可连接表理解和说明的插入语以示强调。

Two of our secretaries—Janet Ross and Henry Lyons—are becoming administrative assistants．

If you want—and I am not sure that you do—to accept the position，we should all be pleased．