一、不定式for结构可以在句中充当主语、宾语、定语、状语、表语等；而不定式of结构在句子中只能作主语。例如：

　　1. It's difficult for a foreigner to learn Chinese.外国人学汉语很难。(主语)

　　2. I'd like for you to go there. 我希望你去那里。(宾语)

　　3. There's a lot of work for me to do. 我有许多工作要做。(定语)

　　4. It's for you to decide.这由你决定。(表语)

　　二、不定式for结构中，不定式的主语可以是人，也可以是无生命的事物，还可以是引导词there；而在不定式of结构中，不定式的逻辑主语只能是表示有生命的人或动物。例如：

　　1. It's important for us to learn foreign languages. 学习外语对我们是重要的。

　　2. It's neccessary for us to have some exercises every day.我们每天需要一些运动。

　　3. It's a pity for there to be any disagreement in the family. 家庭不和睦是遗憾的。

　　4. It's very rude of you to talk like that. 你那样讲话很粗鲁。

　　5. It's selfish of you to keep the money yourself. 你自己把钱留下来是自私的。

　　三、在不定式for结构中，作表语的形容词大多是表示事物性质的，如difficult, heavy, important, possible, necessary等。这些词与for后面的名词(或代词)关系不密切，而与句中的不定式或整个不定式for结构关系紧密，有意义上的主表关系。例如：

　　1. It's difficult for you to get used to the food here. (=For you to get used to the food here is difficult.)你习惯这里的食物是困难的。

　　此句中不定式逻辑主语you与形容词difficult无主表关系，即不能说：You are difficult (to get used to the food here).

　　2. It's not very easy for him to finish the job in time. (=For him to finish the job in time is not very easy.)他及时完成工作是很不容易的。

　　在of不定式的句子中，作表语的形容词大都是表示人物性格、特征的，如：kind, clever, nice, polite, rude, careless等。这些形容词与of后的名词(或代词)有意义上的主表关系。另外，主句的谓语常表示某些感情色彩。例句：

　　3. It's kind of you to say so. (=You are kind to say so.)你这样说太好了。

　　4. It's wrong of you to borrow his book without his permission. (=You are wrong to borrow his book without his permission.) 你没有得到他的允许借用他的书是不对的。

　　同时，这类形容词大多数也可以指不定式行为的性质，也可用于不定式for结构的句子中，但是两种结构在意义上却有所不同。请比较下面两句话：

　　a. It's foolish for you to buy the car.

　　b. It's foolish of you to buy the car.

　　a句强调行为的性质， for只表示一种范围，相当于：For you to buy the car is foolish. (你买那辆汽车是愚蠢的。)它所强调的是"买那辆汽车"这件事，而不是"你"。

　　b句则强调人的特征，即foolish,是you的属性，相当于：You're foolish to buy the car. (你真傻，竟买那辆车。)它强调"你傻"。

　　四、不定式for结构作为主语的句子，可以不用先行词it，而直接用不定式for结构作句子的主语；而不定式of结构一般只能用it作形式主语，不能把不定式of结构提到句首作主语。例句：

　　It's careless of you to lose the bag. ( To lose the bag is careless of you.)你真粗心，竟把包给弄丢了。

　　不可说成：Of you to lose the bag is careless.

　　(文/李海燕 郭辉；英语辅导报小学教师版03~04学年第42期；版权归英语辅导报社所有，独家网络合作伙伴新浪教育，未经许可，不得以任何形式进行转载。)