(1)做形式主語的代詞：
不定式做主語, 通常用it充當(dāng)形式主語, 把做主語的不定式短語后置。 如：
It took me only five minutes to finish the job.
To be frank, it is a great relief to have the task fulfilled in so short a time.
(2)引導(dǎo)邏輯主語的介詞：
不定式的邏輯主語一般由介詞for引導(dǎo),但下列表示人的性格行為特征的形容詞做表語時(shí), 不定式的邏輯主語則由of引導(dǎo)：
absurd, bold, brave, courageous, careful, careless, clever, wise, foolish, silly, stupid, good, nice, kind, thoughtful, considerate, greedy, generous, honest, modest, polite, rude, cruel, selfish, lazy, wicked, wrong。如：
Experts say walking is one of the best ways for a person to stay healthy.
It’s clever of you to have invented such a device.
(3)不定式做主語補(bǔ)足語：
掌握常用不定式做主語補(bǔ)足語的句型。注意不定式表示的動(dòng)作發(fā)生的時(shí)間，并采用相應(yīng)形式。如：
said
reported
thought
be to do sth.
believed
known
supposed
Byron is said to have lived on vinegar and potatoes.
The bank is reported in the local newspaper to have been robbed in broad daylight yesterday.
2.不定式做賓語m.gydjdsj.org.cn
(1)必須接不定式做賓語的動(dòng)詞：
掌握要求接不定式做賓語的動(dòng)詞：
agree, afford, aim, arrange, appear, ask, attempt, choose, claim, decide, desire, determine, expect, fail, guarantee, hope, endeavor, intend, long, mean, manage, offer, ought, plan, pledge, pretend, prepare, promise, proceed, prove, resolve, refuse, request, swear, tend, try, venture, wait, wish。如：
Even though the children pretended to be asleep, the nurses were not deceived when they came into the room.
注意:
1)有的動(dòng)詞要求特殊疑問詞+不定式做賓語, 這類動(dòng)詞有：
consider, discover, explain, forget, guess, know, learn, observe, remember, see, tell, understand, wonder，如：
While still a young boy, Bizet knew how to play the piano well and as he grew older, he wrote operas, the most famous of which is Carmen.
2)如果該特殊疑問詞在不定式中做介詞賓語, 介詞往往置于該特殊疑問詞的前面。如:
The professor can hardly find sufficient grounds on which to base his argument in favor of the new theory.
Without facts, we cannot form worthwhile opinion for we need to have factual knowledge upon which to base our thinking.
(2)可以用不定式做賓語補(bǔ)足語(復(fù)合賓語)的動(dòng)詞：
下列動(dòng)詞可以用不定式做賓語補(bǔ)足語(復(fù)合賓語)：
advise, allow, ask, beg, cause, command, compel, enable, determine, encourage, expect, feel, find, force, hate, have, hear, help, inform, invite, let, like, make, mean, need, notice, notify, oblige, order, permit, persuade, remind, request, require, see, send, teach, tell, tempt, trouble, urge, want, warn, watch, wish。
注意：畫線動(dòng)詞后面的不定式不帶to。
如：
Because of the recent accidents, our parents forbid my brother and me to swim in the river unless someone agrees to watch over us.
