2020军队职称英语语法知识——动词不定式

动词不定式概述
动词不定式指由to加上动词原形所构成的一种非限定性动词，但在有些情况下to可省略。动词不定式在语法功能上可作主语、宾语、表语、定语和状语，如：
To ignore this dangerous signal would be a terrible mistake.（作主语）
He promised not to tell anyone else about it.（作宾语）
To treat comrades like enemies is to go over to the side of the enemy.（作表语）
The manager announced his intention to retire.（作定语）
The old man walked slowly on the ice in order not to fall down.（作状语）
不定式中的动词仍然具有动词的特性，可以有自己的宾语和状语，另外虽然动词不定式在语法上没有表面上的主语，但它所表达的意义是动作，这一动作的执行者就是该动词的逻辑主语，动词不定式要和它的逻辑主语在语态和时态上保持一致。
动词不定式的用法
1.不定式作主语
⑴原则上，可用动词不定式直接作句子的主语，通常用it作句子的形式主语，而把不定式移到后面，形成“It+谓语…+动词不定式…”的句型。如：
To catch the 5：00 bus early in the morning is not a good idea.It is not a good idea to catch the 5：00 bus early in the morning.To learn a foreign language well takes painstaking efforts.It takes painstaking efforts to learn a foreign language well.⑵若要说明不定式的动作的执行者，可以在不定式前面加上“for+名词或代词”结构，或是“of+名词或代词”结构。
It is a great pleasure for me to talk with him.It is very kind of you to help me.⑶可用于“of+名词/代词+动词不定式”结构中作主语补足语的形容词是指那些可以表示人或事物的性质或品质的好坏的形容词。这些词如：careful，cruel，foolish，bold，brave，good，honest，kind，rude，polite，nice，stupid，selfish，silly，wicked，wise，thoughtful，wrong等。
2.不定式作宾语
不定式作宾语有两种情况：一是及物动词后直接跟带to的不定式，二是“动词+疑问词+带to的不定式”。
⑴“动词+带to的不定式”结构：常见的以不定式作宾语的动词有afford，appear，agree，ask，believe，decide，demand，desire，fail，hope，intend，learn，mean，offer，promise，refuse，wish等。如：
I can‘t afford to buy a house.⑵“动词+疑问代（副）词+不定式”结构：常见的这类动词有advise，decide，forget，know，learn，remember，see，tell，think，teach，wonder，discover，understand，guess，explain等。这类疑问代（副）词what，when，which，where，how，whether等（不包含why）。如：
She does not know how to go there.He will tell you how to deal with it.⑶在不定式作宾语时，有时我们会使用it作形式宾语，而把不定式放到后面。如：
They consider it inappropriate to have classes in the evening.
3.不定式作表语
不定式作表语时，主语通常是一个名词，不定式短语或者从句。
The boss‘s plan is to start building the skyscraper immediately.To work means to earn a living.What you have to do is to push the button.
4.不定式作定语
不定式作定语相当于一个定语从句，它修饰以下几类名词：
⑴由动词派生或转化而来的名词，它们所对应的动词通常有不定式作宾语。
Another attempt to climb the mountain will be made next month.In his speech he expressed his determination to achieve the goal.这类名词主要有：attempt，claim，decision，plan，promise，intention，need，resolution，tendency，wish，failure，threat等。
⑵由可能与不定式搭配的形容词派生出来的名词。
Her eagerness to learn a foreign language obvious.这类名词主要有：anxiety，patience，ability，willingness，ambition等。
⑶不定式作定语还可用来修饰代词something，anything，everything，nothing.She has everything to lose and nothing to gain.⑷由only，last，next，序数词或形容词最高级修饰的名词后常用不定式作定语。Jim is the only student to answer the question correctly in his class.You are the last to undertake the blood test.⑸不定式常作为定语修饰there be结构的真实主语。
There is a big task to complete.⑹有些抽象名词。主要有：reason，right，time，effort，chance，way等。如：the time to go to school，the way to get to the clinic，the chance to win the game.
5.不定式作状语
不定式作状语相当于一个状语从句，表示形为的目的、结果或原因。
⑴表示目的。在这种情况下，不定式的逻辑主语通常也是全句的主语。
He stayed there to see what would happen.在强调不定式目的状语时，不定式前可加in order，so as等。如：
She asked me to drive her to the airport in order to catch the 5：00 plane.He moved the TV set to the meeting-room so as to let everyone watch it.
⑵用so……as to……，such（……）as to……，enough to……，too……to，only to等表示结果，如：
Have you got enough room to seat all of us？
She is too weak to join us in the outing.
⑶将不定式移到句首表示条件，如：
To hear the teacher better，you have to sit in the front.=If you are to hear the teacher better，……
⑷与形容词连用时，大多表示原因。这些形容词主要有：happy，kind，surprised，frightened，angry，shocked，glad，delighted，grieved，disappointed等。
They were surprised to be informed of the news.I‘m glad to hear this.
动词不定式的时态和语态
一般式to do to be done
完成式to have done to have been done
进行式to be doing
完成进行式to have been doing
1.如果不定式所表示的动作与主要谓语动词所表示的动作同时（或几乎同时）发生或发生在主要谓语之后，通常用不定式的一般形式。如：
I saw him go out.
I‘m glad to see you.
2.如果不定式所表示的动作发生在主要谓语动词或特定的时间之前，不定式就要用完成式。如：
I intended to have telephoned you，but I forgot to.
I should like to have bought a dictionary.
3.不定式进行式表示主要谓语动词所表示的动作发生时，不定式所表示的动作正在发生。如：
I am glad to be talking with you.She pretended to be listening attentively.
4.不定式完成进行时表示的是一个开始于过去某一时刻但一直延续到谓语动词发生的那一时刻的动作。如：
He was thought to have been working on the project for two years.
5.不定式的被动语态
当不定式的逻辑主语是动作的承受者时，这个不定式要用被动式，包括它的各种时态在内。如：
She doesn‘t like to be treated as a guest.
她不喜欢被当作客人对待。
They want their TV set to be fixed right now.
他们想把电视机马上修好。
There are a lot of things to be done.
有许多事要做。
This is the text to be read next time.
下次就读这篇课文。
注意：有些习惯用法中，只能用主动语态。如：
The house is to let.
这房子要出租。
A lot of work still remains to do.
许多工作有待去做。
不带to的不定式
1.表示感觉的动词see，hear，feel，notice，watch，observe和have，let，make后的宾语可接不带to的不定式。
He noticed the man enter the room.
他注意到有人进屋了。
They observed her do the experiment.
他们观察她做实验了。
2.help后的不定式可以带to也可以不带to.
Can you help me（to）clean up after the meal？
饭后你能帮我洗碗吗？
3.有些类似于情态动词的词语（如rather than，had better，would rather，might as well等）之后，不定式不带to.如：
We might as well go without him.
我们可以不让他跟去。
You‘d better go now.
你最好现在走。