动词不定式
动词不定式是动词的一种非谓语形式，在句中不能单独作谓语。动词不定式具有动词的性质，它可以有自己的宾语和状语，从而构成动词不定式短语。它还可以有形式的变化，即一般式、进行式、完成式和被动式。同时，动词不定式也具有非动词的性质，相当于一个名词、形容词或副词，可以在句中担任主语、宾语、宾语补足语、表语、定语和状语。
一、 动词不定式的特征和种类
动词不定式是由不定式符号to+动词原形构成，在某些情况下to也可省略。
A． 不定式的一般式
不定式的一般式表示的动作通常与主要谓语的动作同时或几乎同时发生，或是在它之后发生。 To do
He appears to be very happy.
B．不定式的进行式 to be doing
不定式的进行式表示正在进行的或与谓语动词同时发生的动作。
It happened to be raining when I got there.
I'm glad to be traveling with you.
C． 不定式的完成式 to have done
不定式的完成式表示的动作在谓语表示的动作之前发生。
I'm sorry to have lost your key.
I meant to have finished my work last night, but I didn't feel very well.
It has been an honor for me to have been invited to your country.
D． 不定式的完成进行式 to have been doing
不定式的完成进行式表示的动作在谓语之前发生并且一直进行着。
He was said to have been living in London for twenty years.。
I'm sorry to have been interrupting you.
E． 不定式的被动形式
当不定式逻辑上的主语是这个不定式表示的动作的承受者时，不定式一般要用被动形式。不定式的被动形式根据其与谓语动作发生的先后关系，有一般式和完成时两种。
1．一般式 to be done
These are the books to be given out to the students.
He asked to be sent to the place where he was most needed.
2．完成式 to have been done
The novel is said to have been translated into many languages.
F. 不定式的否定形式
不定式的否定形式由not或never加不定式构成。
We decided not to go out because of the bad weather.
Never to have made any mistake is impossible.
二、 动词不定式的用法
A．动词不定式作主语
1．不定式短语在句首作主语
To know oneself is difficult. To say is one thing and to do is another.
2．用it作形式主语
在很多情况下，人们通常用it作为形式上的主语，而把不定式移到谓语之后，
It's rude to turn your back to your teacher and refuse to answer.
It seemed a pity to have wasted so much time.
注意：
当主语和表语都是不定式时，不能用形式主语代替动词不定式。
To respect others is to be respected.
It is + 形容词 + forof sb + to do 结构
在“It is +形容词+ of sb +不定式”结构中，形容词往往表示人物的性格和特征，如kind, silly, good, unwise, clever, wrong, right, foolish, stupid, careless, rude, impolite, bold, thoughtful, honest, bad, sensible, naughty等。在“It is +形容词+for sb +不定式”结构中，形容词通常表示事物的性质，如important, possible, impossible, necessary, difficult, hard, reasonable等。
It's kind of you to think so much of us. It is easy for me to see through his trick.
It is hard for him to get rid of his bad habits.
B． 动词不定式作表语
不定式作表语可以说明主语的具体内容或表示目的。
His wish is to become an astronaut.
What he hoped was to be admitted into the university.
注意：
有些作表语的不定式，在结构上是主动的，但在意义上却是被动的。
She is to blame. The house is to let. 此房出租。
C． 动词不定式作宾语
不定式可以充当部分及物动词的宾语，也可以充当but和except等介词的宾语以及形容词的宾语。
1．作动词的宾语
①不定式可以充当部分及物动词的宾语。
Father likes to listen to music in silence.
He prefers to be starved to death rather than beg.
必背：
可接不定式作宾语的动词有：
afford负担得起 agree 同意 aim以……为目标 ask 要求 attempt 尝试 begin 开始 care喜爱 choose决定 continue 继续 decide 决定 desire 要求 determine决心 expect 期待 fail不能 forget 忘记 hate不愿 hope 希望 ntend 打算 manage设法 mean 打算 offer表示愿意 plan 计划 prefer 宁愿 pretend 假装 promise 答应 refuse 拒绝 remember记起 try努力 want 想要 wish希望
②在feel, find, make, think, consider等动词后，如果宾语带有宾语补足语时，人们常常用it作形式宾语，而把真实宾语放在宾语补足语之后。
I found it possible to work out the problem without a computer.
She made it a rule to get up at five.
③在表示“希望、打算”等动词（如hope, expect, intend, mean, want等）的过去式后，可接动词不定式的完成式来表示没有实现的动作。
I intended to have called on you, but was prevented from doing so.
I expected to have met him here last night.）
2．作介词的宾语
不定式可以作介词but和except的宾语。
The teacher made no comments except to tell him to work hard.
He had no choice but to sit there as usual.
There is nothing we can do but wait patiently.
3．作形容词的宾语
不定式作形容词的宾语有两种句型，一个是句子的主语是不定式的逻辑主语，另一个是句子的主语是不定式的逻辑宾语。
①句子的主语是不定式的逻辑主语。这类形容词有able, afraid, angry, anxious, careful, clever, content, cruel, determined, disappointed, eager, foolish, fortunate, frightened, happy, impatient, glad, lucky, naughty, prepared, proud, ready, slow, shocked, sorry, surprised, willing等。
I am sorry to say that he is going from bad to worse.
She was not content to live a quiet life in a small town.
②句子的主语是不定式的逻辑宾语。这类形容词有easy, hard, cheap, expensive, dangerous, difficult, funny, fit, impossible, interesting, nice, pleasant, simple, strange, useful等。
This problem is easy to solve. The water is not fit to drink.
She is hard to get along with.
注意：在这种结构中，如果不定式是不及物动词，则必须加上结构或含义所需的介词。
The river is dangerous to swim in. A spring mattress is comfortable to sleep on.
D． 动词不定式作宾语补足语
不定式可以在“主语+谓语+宾语+宾语补足语”句型中充当宾语补足语。在这一句型中，宾语是动词不定式的逻辑主语。
1．在表示感觉的动词后作宾语补足语，并且不定式都不带to。这类动词有：see, hear, feel, watch, notice, observe, look at, listen to等。
I heard them sing yesterday.
Did you see him go out
转为被动语态时，原不带to的不定式要变成带to的不定式。notice和watch没有被动语态。
We saw the car stop. The car was seen to stop.
2．在使役动词后作宾语补足语，不定式不带to。
：make, let, have等。转为被动语态时，其后通常都用带to的不定式（have没有被动语态）。
有些动词跟不定式作宾语补足语时省去了to，这些动词有：
一感二听三让四观看。
一感：feel 二听：hear,listen to 三让：let,have,make 四观看：observe,see,watch.,look at
What would you have me do
She made him give up smoking.
3．在表示心理状态的动词后作宾语补足语。这类动词有：consider, think, believe, discover, find, imagine, judge, suppose, prove等。这类动词后的不定式通常是“to be+形容词或名词”结构，think, consider, find后的to be常可省略。
We consider him (to be) a good teacher.
He proved that theory (to be) very important.
4．在表示情感状态的动词后作宾语补足语。这类动词有：love, like, prefer, hate, want, wish, expect等。
I'd prefer you to leave him alone. I don't want there to be any trouble.
5．动词advise, allow, ask, beg, command, tell, invite, force, oblige, get, help, encourage, persuade, permit, remind, request, order, warn, cause等后面，多接不定式短语作宾语补足语。
We don't allow such things to happen again.
Most of the parents agree to forbid their children to smoke.
注意：hope, demand, suggest等动词后面不能接不定式作宾语补足语。
E． 动词不定式作定语
不定式做定语通常要放在被修饰的词后，往往表示未发生的动作。例如：
I have a lot of work to do.
There was nothing to bring home that morning.。
F． 动词不定式作状语
不定式作状语可以表示行为的目的、结果、原因、条件等。
1．表示目的
I'm saving up to buy a computer.
To save the child, he laid down his life.
注意：有时为了强调或突出这种目的，也可以用in order (not) to do,和so as (not) to do结构（so as to do不可以置于句首）。
He shouted and waved in order to be noticed. 为了吸引注意，他又嚷嚷又挥手。
2．表示结果
He got to the station only to find the train had gone.
What have I said to make you so angry
3．表示原因
I was a fool not to listen to you at that time.
She wept to find him in such a difficult situation.。
4．表示条件
A man would be blind not to see that.
How can you catch the train to start so late