for ⁴

当 for 引导的时间短语用来修饰具有静态意义的动词时常常可以省略：

1. They lived in China (for) seven years.

2. The meeting lasted (for) two hours.

3. We stayed at the hotel (for) three weeks.

4. He has worked here (for) a year.

5. They will be in Chicago (for) a year.

当 for 与以 all 开头的名词短语连用时, 必须省略 for[参见 for all day(×)] :

但是，当 for 短语修饰动态动词时或者用于否定句时，则介词 for 不能省略。

1. I'm going away for a few days. 我要离开几天。

2. I haven't seen him for three weeks. 我有三个星期没有看见他了。

所以,CGEL 把下列句子看作是错误的:

1. × I taught her three years.

2. × I haven't spoken to her three months.

另外, 当 for 用在句子开头时, 一般也不能省略:

1. $\$left\{\begin{array}{l}He lived abroad (for) six years.\\ For six years, he lived abroad.\end{array}\right. 他在国外住了六年。

2. He waited anxiously at hospital (for) some time.

For some time, he waited anxiously at hospital. 他在医院焦急地等了一会儿。