It was kind of you...
It's very kind of you to think so much of us. 请问这里为什么用 of you, 而不用 for you?
It is quite impossible for me to learn French. 这个句子可以改为: For me to learn French is quite impossible. 但是 It's very kind of you to think so much of us. 却不能改为: Of you to think so much of us is very kind. 而应改为: You are very kind to think so much of us. 这说明上面的两个句子分别归属于两个不同的句型。for you 用于引出动词不定式的逻辑主语, 而 of you 则在某些具有评价人物行为意味的形容词之后, 点明形容词所涉及的对象, 因而应当把 of you 看作是与形容词连接在一起的(形容词的补足成分)。这类评价人物行为的形容词是有限的, 其中包括: kind, nice, good, careful, careless, crazy, foolish, silly, wise, stupid, rude, impolite, right, wrong, considerate, brave, clever, selfish, wicked。
请注意这种句型的实质：
It was foolish of you to spend so much.
You were foolish to spend so much. 你花费那么多钱太傻了。
It was wrong of him to tell lies.
He was wrong to tell lies. 他撒谎是错误的。
It's very nice of you to be so considerate.
You are very nice to be so considerate. 你这么体谅人，真是太好了。