1.不定式的構成
1）不定式的一般式，不定式的一般式所表示的動作通常與主要謂語的動作同時或幾乎同時發生，
或是在它之后發生。
They invited us to go there this summer.
他們邀請我們今年夏天去那兒。
He stood aside for me to pass.
他站到一邊讓我通過。
2) 不定式的完成式. 不定式的完成式所表示的動作在謂語所表示的動作之前發生，它在 句中可作表語、狀語、賓語，有時也可作主語、定語等。如：
She seemed to have heard about this matter.
她似乎已聽說過這件事。
I am sorry to have kept you waiting so long.
我很抱歉讓你等了這么久。
I meant to have told you about it, but I happened to have an important thing to do.
我本來想告訴你這件事的，但我碰巧有一件重要的事要做。
It has been an honor for me to have traveled so much in your country.
對我來說，在你們國家旅行這么多地方是一件很榮幸的事情。
3) 不定式的進行時. 不定式的進行時表示正在進行的與謂語動詞同時發生的動作。它在句中可以用作除謂語以外的所有成分。如：
He pretended to be listening to the teacher carefully.
他假裝在認真地聽老師講課。
4) 動詞不定式的否定形式是由not或never加不定式構成。
Try not to be late again next time.
盡量下次不要再遲到。
He wished us never to meet her again.
他希望我們永遠不要再見到她。
5) 疑問詞+動詞不定式：
不定式和疑問詞whether, what, which, whom, where, when, how, why等連用可以在句中起名詞的作用，通常跟在tell, know, show, decide, learn, wonder, explain, advise, teach, discuss, find out等動詞后面作賓語，有時也可以充當主語、表語等。如：
On hearing the news, he didn't know whether to laugh or to cry.
聽到這個消息，他不知道該哭還是該笑。
When to hold the meeting has not decided.
什么時候開會還沒有決定。
The most important problem is how to get so much money.
最重要的事情是如何搞到這么多錢。
介詞后一般不直接接不定式，但可以接疑問詞+不定式短語作賓語。如：
Mary gave some advice on how to learn English.
瑪麗提了一些如何學習英語的建議。
I have no idea of how to do it.
我不知道該怎么做。
2.不定式的語法作用.
1) 不定式作主語：
To see once is better than to hear a hundred times.
百聞不如一見。
To master a foreign language is not an easy thing.
掌握一門外語不是一件容易的事。
在很多情況下，人們通常用it作為形式上的主語，而把不定式短語移到謂語之后，使句子顯得平穩一些。如：
It's good manners to wait in line.
排隊等候是很有禮貌的。
It made us very angry to hear him speak to his mother like that.
聽到他那樣跟他媽媽說話我們很生氣。
2) 不定式作表語：
The most important thing is to put theory into practice.
最重要的事情是把理論付諸實踐。
The greatest happiness is to work for the happiness of all.
最大的幸福就是為大家的幸福而工作。
I feel it a great honor to be invited to speak at the meeting before so many students.
我覺得被邀請在會上面對這么多學生發言是一件很光榮的事情。
4) 不定式作補語：.
①不定式可以和名詞或代詞一起構成復合結構作動詞的賓語，這時不定式被稱為賓語補足語。如：
I would like you to help me with my English exercises.
我想請你幫我做英語練習。
I never expected the shoes to be worn out so soon.
我從來沒想到鞋這么快就穿破了。注意：動詞help后面接不定式作賓語或賓語補足語可以帶to也可以不帶to。如：Who can help me
(to) carry this heavy box?
誰能幫我拎這個重箱子？
②在make, let, have等使役動詞和see, watch, notice, hear, feel等感官動詞后的復合賓語中，動詞不定式不帶to。
I often hear her sing in the next room.
我經常聽到她在隔壁唱歌。
They make the baby go to bed at 7:00 p.m. every day.
他們每天讓孩子晚上7：00上床睡覺。
注意：當使役動詞和感官動詞變為被動語態時，不定式就成了主語補語，作主語補語的不定式必須加to。如：
Though he had often made his little sister cry, today he was made to cry by his little sister.
盡管他經常弄哭他的小妹妹，但今天他卻被他的小妹妹弄哭了。
He is often heard to sing the song.
經常有人聽到他唱這首歌。
③以be said, be reported, be known, seem, happen, prove, appear等構成謂語的句子中，動詞不定式通常也可看作主語補語。如：
More than 20 people were reported to have been killed in the accident.
據報道，有20多個人死于事故。
I happened to be talking with him when he was hit by a car.
他被汽車撞的時候，我碰巧在和他談話。
5)不定式作狀語：
不定式作狀語可以表示行為的目的、結果、原因、條件等。
1 不定式作目的狀語，有時也可以用in order (not) to, so as (not) to結構。如：
In order to protect the young plants from the sun, Mother put them in the shade.
為了保護幼苗不被太陽曬壞，媽媽把它們放到了陰涼處。
He got up very early this morning so as not to be late for school again.
今天早上他起身很早以免上學再遲到。
2 不定式作結果狀語，常見的結構有too…to, enough…to, so…as to, such…as to, only to…等。
The question is too difficult for me to answer.
對我來說，這個問題很難回答。
He said he was clever enough to deal with it by himself.
他說他足夠聰明可以獨自應付這件事。
Will you be so kind as to turn down the radio?
請你幫我把收音機調低一點好嗎？
He woke up only to find himself in hospital.
他醒來發現自己在醫院里。
③不定式作原因狀語，通常用來修飾表示情感、心理狀態、性格等的形容詞。
They are surprised to learn of his death.
得知他死亡的消息，他們很驚訝。
We are proud to be young people of new China.
成為新中國的青年，我們感到很驕傲。
hard, difficult, easy, fit, comfortable等詞也可以接動詞不定式。如：
The water is not fit to drink.
這水不適合飲用。
The room is very comfortable to live in.
這個房間住起來很舒服。
2.不定式的復合結構.
It's expensive for people to use electricity for cooking.
人們用電做飯是很昂貴的。
It's careless of you to make such a mistake.
你犯這樣的錯誤真是粗心。
They thought it impossible for us to find the lost child in the darkness.
他們認為我們要在黑暗中找到迷路的小孩是不可能的。
難點釋疑：
1.不定式不帶to的規則：
前面我們已經談到，在一些使役動詞和感官動詞后的不定式作賓語補語時，不定式符號to常常省略，下面還有幾種情況請大家注意：
1 在why引起的一些疑問句中，疑問詞直接跟動詞原形或not+動詞原形。如：
Why spend so much money?
為什么花這么多錢？
Why not let her have a try?
為什么不再讓她試一試？
②在had better（還是……最好）, had best（最好，頂好）, would rather（寧可，寧愿）, would rather…than（寧可……而不……）, would sooner（寧可，寧愿）, would sooner…than（寧可……而不……）, cannot but（不得不，必然）, cannot choose but（只得）, cannot help but（不得不）等結構后直接跟動詞原形或not +動詞原形。如：
You'd better listen to your teacher's opinion.
你最好聽一聽老師的看法。
I would rather work than stay idle.
我寧愿工作而不愿閑坐。
Rather than ride on a crowded bus, he always prefers to ride a bicycle.
他寧愿擠公共汽車也不愿騎自行車。
Liu Hulan would sooner die than surrender.
劉胡蘭寧死不屈。
One's world outlook cannot but come through in what one says and does.
一個人的世界觀必然在他的言行中表現出來。
③在介詞but, except之前如有動詞do的任一形式，其后的動詞不定式不用to。如：
Last evening I did nothing but repair my farm tools.
昨晚上我除了修理農具外，沒有做其它的事情。
Now there was nothing he could do except admit defeat.
現在他只有認輸。
如but之前沒有do，其后的不定式則一般要加to。如：
I'm afraid we have no choice but to take a taxi.
恐怕我們別無選擇，只好乘出租車了。
They desired nothing but to succeed.
他們只想成功。
2. for somebody to do和of somebody to do的用法區別：
句型“It is +形容詞+for somebody+不定式”中的形容詞通常強調不定式的行為屬性，如：important, possible, impossible, necessary, difficult, hard, reasonable等。
It's difficult for us to finish the work within two hours.
我們要在兩小時之內完成工作是很難的。
It's reasonable for them to run away so quickly.
他們這么快就逃跑了是很有道理的。
“It is +形容詞+of somebody+不定式”中的形容詞表示人物性格和特征。如：
kind, silly, good, unwise, clever, wrong, right, foolish, stupid, careless, rude, impolite, bold, thoughtful, honest, bad, sensible, naughty等。
It's kind of you to think so much of us.
難為你這么為我們著想。
It's silly of the boy to keep pouring water into the basket.
這個男孩真傻，一直往籃子里倒水。
