for you 是不定式的逻辑主语。说明不定式的动作是you 发出的。

不定式都有自己的逻辑主语，它可能是句子的主语、宾语，也可能是由for或of引出的名词或代词。那么，这类带有逻辑主语的不定式称为不定式的复合结构。

（1）逻辑主语是句子中的某个成分。

I have several e-mails to send today.今天我有些电子邮件要发。（to send的逻辑主语是I）

The mother promised to buy her son a cell phone.

那位妈妈答应给她儿子买手机。（to buy的逻辑主语是the mother）

The teacher encourages the boy student to study harder.

老师鼓励那位男生更加努力地学习。（to study的逻辑主语为the boy student）

（2）由for 引出不定式的逻辑主语。

若不定式前的形容词说明不定式的性质，其逻辑主语一般用for引出。

It's common for leaves to fall from the trees in autumn.

在秋季树叶从树上落下来，这是很平常的。

It's for you to decide.这得由你决定。

There are a lot of difficulties for us to overcome.有许多困难等待我们去克服。

He put the newspaper on the desk for you to read.他把报纸放在桌子上让你看。

（3）由of 引出不定式的逻辑主语。

不定式前的形容词描述的是不定式逻辑主语的品质、身份、特征时，该逻辑主语用of引出。这时，逻辑主语与前面的形容词构成主表关系。

It is kind of you to help us.(=You are kind to help us.)你帮助我们真是太好了。

It was silly of you to trust such a man.(=You were silly to trust such a man.)

你太愚蠢了，竟然相信这样一个人。

It is selfish of him not to do anything for the orphans.(=He is selfish not to do anything for the orphans.)他很自私不愿为孤儿们做点事。

It's unfair of you to say such things about her.(=You are unfair to say such things about her.)你这样说她太不公平了。

用于“It is/was+ adj.+of sb.to do sth.” 结构的形容词：

kind, nice, good, polite, impolite, rude, patient, careful, careless, wise, clever, selfish, unselfish, foolish, silly, stupid, cruel, brave, crazy 等。