在上述情況下，如果不定式較長(zhǎng)，顯得頭重腳輕，則可由代詞讓作形式主語(yǔ)(形式主語(yǔ)it不可由that或this等其他代詞代替)，而將不定式放到后面。如：

　　1.It made him extremely happy to get contact with his family in Taiwan since they separated more than 40 years ago.

　　2.John admitted that it is always difficult for him to be on time.

　　不定式結(jié)構(gòu)所表示的動(dòng)作是誰(shuí)做的，即不定式的邏輯主語(yǔ)，通�？梢酝ㄟ^(guò)for sb. to do sth. 結(jié)構(gòu)表達(dá)：

　　1.It is quite important for us to read good books during a general review.

　　2.It is not difficult fot those talented students to pass the exam.

　　在某些形容詞(如careless，clever，considerate，foolish，good，impolite，kind, naughty，nice，silly，stupid等)作表語(yǔ)時(shí)，不定式后可以加of來(lái)引導(dǎo)出其邏輯主語(yǔ)：

　　1.It is very kind of you to tell me the truth.

　　2.It is stupid of him to do such a silly thing.

　　2)不定式作賓語(yǔ)

　　不定式作賓語(yǔ)有兩種：一種是及物動(dòng)詞后直接跟帶to的不定式, 另一種是“及物動(dòng)詞+疑問(wèn)詞+帶to的不定式。

　　及物動(dòng)詞+帶to的不定式結(jié)構(gòu):

　　只能跟動(dòng)詞不定式的動(dòng)詞，常見的有: afford, agree, aim, appear, ask, believe, care，claim，decide demand, desire, determine, expect, fail, happen, hesitate, hope, intend, learn, long, manage, offer, pretend, promise, prepare, refuse, seek, swear, undertake，want, wish等。

　　1.He managed to solve the complicated problem.

　　2.The stranger offered to show me the way.

　　3.Mr. Smith undertook to build a new plant in South Africa.

　　動(dòng)詞+疑問(wèn)代(副)詞+不定式：

　　這類動(dòng)詞常見的有advise, decide, find out, forget, inquire, know, learn, see, regard, remember, teach, tell, understand, wonder等。常見的疑問(wèn)代(副)詞有: what, when, where, which, how, whether等。

　　1.He does not know when to start.

　　2.You can decide whether to continue or to stop.

　　3.I will show you how to deal with it.

　　有時(shí)，不定式可由it代替，而把不定式放到后面去。這可以用這一結(jié)構(gòu)表達(dá)：動(dòng)詞(如find, think，consider，feel等)+it+ 形容詞+不定式。

　　1.She considers it necessary to make friends with him.

　　2.We find it difficult to finish all the homework before 9 o’clock.

　　3)不定式做表語(yǔ)

　　一種情況為主語(yǔ)是不定式(表示條件);表語(yǔ)也是不定式(表示結(jié)果)：

　　1.To see is to believe.

　　2.To work means to earn a living.

　　另一種情況為主語(yǔ)是以aim，duty，hope, idea，job, plan，problem, purpose，thing，wish等名詞為中心的短語(yǔ)，或以what引導(dǎo)的名詞性從句，不定式表語(yǔ)對(duì)主語(yǔ)起補(bǔ)充說(shuō)明作用：;例如：

　　1.His aim is to study abroad in the near future.

　　2.The most important thing is to negotiate with them about the price.

　　3.What I want to say is to forget all the unhappy experience.

　　4)不定式作定語(yǔ)

　　不定式結(jié)構(gòu)作名詞詞組修飾語(yǔ)主要有三種類型：

　　第一種，被修飾的名詞詞組是不定式的邏輯賓語(yǔ)。例如：

　　1.There was really nothing to fear.

　　2.He gave me an interesting book to read.

　　如果不定式是不及物動(dòng)詞，后面就得加相應(yīng)的介詞。例如：

　　1.Mary needs a friend to play with.

　　2.That girl has nothing to worry about.

　　3.They have a strict teacher to listen to.

　　4.Although the film had been on for ten minutes, I still was not able to find a chair to sit on.

　　第二種，被修飾的名詞詞組是不定式的邏輯主語(yǔ);例如：

　　1.Have you got a key to unlock the door?

　　2.The action to be taken is correct.

　　3.There is nothing to be gained by pretending.

　　第三種，被修飾的名詞詞組是不定式的同位結(jié)構(gòu)。這類名詞通常是表示企圖、努力、傾向、目的、愿望、is算、能力、意向等意義的名詞：ability, attempt, effort, impulse, inclination,wish等。例如：

　　1.Her daughter will make an even bigger effort to please her.

　　2.I have no wishto quarrel withyou.

　　3.Neither of them had any inclination to do business with Mary.