2.不定式的句法功能：

　　(1)作主語(yǔ)：

　　To finish the work in ten minutes is very hard.

　　To lose your heart means failure.

　　動(dòng)詞不定式短語(yǔ)作主語(yǔ)時(shí)，常用it作形式主語(yǔ)，真正的主語(yǔ)不定式置于句后，例如上面兩句可用如下形式：

　　It is very hard to finish the work in ten minutes.

　　It means failure to lose your heart.

　　常用句式有：1、It+be+名詞+to do。2、It takes sb.+some time+to do。3、It+be+形容詞+of sb +to do。4、It+be+形容詞+for sb.+to do。常用careless,,clever,good,foolish,honest,kind,lazy,nice,right,silly,stupid,wise,等表示贊揚(yáng)或批評(píng)的形容詞，不定式前的sb.可作其邏輯主語(yǔ)。

　　(2)作表語(yǔ)：

　　Her job is to clean the hall.

　　He appears to have caught a cold.

　　(3)作賓語(yǔ)：

　　常與不定式做賓語(yǔ)連用的動(dòng)詞有：want, hope, wish, offer, fail, plan, learn, pretend, refuse, manage, help, agree, promise, prefer, 如果不定式(賓語(yǔ))后面有賓語(yǔ)補(bǔ)足語(yǔ)，則用it作形式賓語(yǔ)，真正的賓語(yǔ)(不定式)后置，放在賓語(yǔ)補(bǔ)足語(yǔ)后面，例如：

　　Marx found it important to study the situation in Russia.

　　動(dòng)詞不定式也可充當(dāng)介詞賓語(yǔ)，如：

　　I have no choice but to stay here.

　　He did nothing last Sunday but repair his bike.

　　動(dòng)詞不定式前有時(shí)可與疑問(wèn)詞連用，如：

　　He gave us some advice on how to learn English.

　　(4)作賓語(yǔ)補(bǔ)足語(yǔ)：

　　在復(fù)合賓語(yǔ)中，動(dòng)詞不定式可充當(dāng)賓語(yǔ)補(bǔ)足語(yǔ)，如下動(dòng)詞常跟這種復(fù)合賓語(yǔ)：want, wish, ask, tell, order, beg, permit, help, advise, persuade, allow, prepare, cause, force, call on, wait for, invite.

　　此外，介詞有時(shí)也與這種復(fù)合賓語(yǔ)連用，如：

　　With a lot of work to do, he didn't go to the cinema.

　　有些動(dòng)詞如make, let, see, watch, hear, feel, have等與不帶有to的不定式連用，但改為被動(dòng)語(yǔ)態(tài)時(shí)，不定式要加to, 如：

　　I saw him cross the road.

　　He was seen to cross the road.