引号

在直接引用某人说过的话时，会用到引号。但如果是转述某人说过的话，就不用引号。

举例

"I'm going to the store now," she said.
Harry told me, "Don't forget your soccer jersey."
Harry told me not to forget my soccer jersey.

如果要在引用句中再引用他人的话语，就会用单引号和双引号来区别两句引文。

举例

'I haven't spoken to Peter for months,' Dianne said.'The last time I spoke to him he said, "I'm going to Bahrain and won't be back for about three years", I've heard nothing since then'.

用单引号或双引号来表示谚语或不熟悉的说法

举例

I've always thought that he was very annoying, a bit of a 'pain in the neck.'
I'm not sure what you mean by "custodial care", but I'm sure you will explain it to me.

在学术写作上，会用单引号或双引号来标明文献或资料来源。文献引用书写格式有好几种，学术机构一般会有偏好的一种写法，他们有时会在网站或简章上公布指定的格式。