先行詞it的幾類句型

先行詞it在主語或賓語的位置，真正的主語或賓語是后面的不定式、動名詞或名詞性從句。

一、作形式主語

主要用于It is+ adj. /n. + doing/to do/從句…句型。
Is it necessary for me to do so? 我有必要這樣做嗎？
It is silly of him to do so. 他這樣做真是可笑。
It’s no good waiting here. 在這里等沒有用。
Is it certain that they will win? 他們一定會贏嗎?
It’s my duty to help you improve English. 幫助你們提高英語水平是我的職責。
注意：與it作形式主語的句型易混的句型。
It is known to all that the earth goes around the earth. 眾所周知，地球圍繞太陽旋轉。
As is known to all, the earth goes around the earth.
It is difficult to persuade him to stay. 勸服他留下來很難。
What is difficult is to persuade him to stay. 困難的是要勸服他留下來。

二、作形式賓語
1. vt. (find, think, make, etc. ) + it +adj. /n. +doing/ to do/that…
He made it a rule never to eat between meals. 他不吃零食已成了習慣。
I think it impossible for us finish our work on time. 我認為我們不可能準時 完在這項工作。
We found it no good arguing with him. 同他爭論是沒用的。
I’ll make it clear to you that failure is the mother of success. 我要告訴你們失敗的成功之母。
I’d think it well worth while to go. 我覺得很值得一去。

2. vt. (enjoy, like, love, hate, prefer, appreciate, take, etc.) +it+ if /when…
I don’t like it if you arrive late. 我不喜歡你遲到。
She hates it when he uses her pen. 她討厭他用她的鋼筆。
I take it you have been out. 我猜你剛出去回來。
You can put it that it was arranged before. 你可以說這是以前安排的。

3. see to it that…/depend on it that…(因介詞后通常不接that從句，故用it作形式主語)
See to it that you are not late again. 注意別再遲到了。
You may depend upon it that we shall never lose heart. 你放心我們絕不會灰心。

4. take it for granted that…等
I took it for granted that you would stay with us. 我肯定你會住在我們這里的。