动词不定式
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第四章动词不定式第一节概述动词不定式是一种非谓语动词形式,它具有以下特征:1.在句中不受主语人称和数的限制,也不体现“时(tense)”的特征。
2.具有动词性质。
表现在它有:1)“体(aspects)”和语态的变化2)可以有自己的宾语和状语,一起构成动词不定式短语。
第二节不定式的语法功能一、用作主语1.不定式结构可直接置于句首做主语,此时谓语动词要用单数。
e.g. To err is human; to forgive, divine.2.更常见的是用it 作形式主语放在句首,将真正的主语动词不定式放在句子后面。
(注意:此处形式主语it 不能用this 或that 来替换)a)It is not easy to anwser this question in one go.b)改错:Due to the refraction of light rays, this is impossible for the naked eye to determine the exactlocation of a star close to the horizon.3.有时不定式还引出自己的逻辑主语,来说明不定式动作的执行者。
a)It’s important for you to go there in person.规律:看句中的表语形容词是看重说明人(逻辑主语),还是事(不定式短语)。
若是前者,则用of;若是后者,则用for。
且用of的句子,可以用人做主语将句子改写;用for的句子则不能。
与wise 类似的形容词还有:kind, honest, bad, stupid, bold, clever, cruel,nice, rude, sensible, tactful, silly, thoughtful, considerate等等。
这些形容词都用来描写人的特征,故要用of 引出其逻辑主语。
这些结构还可用how 强调,其结构为:a)How wise of you (it is) not to argue with your boss.b)How silly of you to always ask this question.二、用作主语补足语1.用作表语a)The duties of a postman are to deliver letters and newspaper.b)The best thing would be for you to work out a definite plan2.用作主语补足语在下例句中,主语和由不定式充当的主语补足语,二者在逻辑上是主谓关系。
a)He is said to be from China by origin.b)The young man was considered to show great promise.三、用作宾语1.直接跟在一个及物动词后面作宾语。
第一,句中主语和不定式的逻辑主语是一致的,即两个动词所表示的动作都有全句主语发出。
第二,这时句子的谓语动词多是描写态度,不定式的动词则说明行为。
a)I hope to see you again.b)Mr. Chairman, I beg to move that the meeting be adjourned.2.不定式作复合宾语中的宾语。
此时往往用it 作形式宾语,而将真正的宾语放在宾语补足语后面。
常用于此结构中的动词有:consider,think,judge,feel, make等。
此时,句子主语一般也是不定式的逻辑主语,即两个动词表示的动作都由全句主语发出。
a)I think it hard to anwser the question in one go.b)He feels it challenging to be a marketing supervisor.3.不定式用在一些动词之后。
可以在连接代词(what,who,which)或连接副词(how,when,where)及连词whether后面接一个带to的动词不定式。
我们可以将这种结构看成是连接词引导的宾语从句的简略形式。
a)I wonder who to invite.b)Show us what to do.c)I don’t know whether to answer his letter四、不定式用在形容词后1.句子主语和不定式动词可构成逻辑上的主谓关系。
a)I am sure to come.b)He was surprised to learn how much he had spent.2.句子主语和不定式动词可构成逻辑上的动宾关系。
a)Relativity theory isn’t easy to understand.b)Football is very interesting to watch.c)English is difficult to speak.在句子主语与不定式动词存在这种动宾关系的情况下,我们要注意以下三点:1)不定式后不能再加宾语:a)Football is very interesting to watch (it)*b)She is nice to talk to her*2)不定式动词所带的介词不能省略:a)She is interesting to listen.*b)She is easy to get on (*3)不定式动词一般不用被动式:a)English is difficult to be spoken.*b)Football is interesting to be watched.*五、用作宾语补足语1.通常的结构是:动词+sb.(to) do sth.,这里的to有时要省略,这取决于前面的动词。
a)They don’t allow people to smoke in the theatre.b)The chairman declared the meeting to be over.2.在let,make,have,see,hear,feel,watch,notice,listen to等动词后面的不定式作宾补的句子中,to 要省略。
若改为被动语态,则需带to。
3.在believe,consider, declare, find, feel, imagine, know, prove, suppose, think等动词后面,不定式作宾补常是to be形式。
a)I think him to be an excellent choice.b)We believe her to be innocent.在这种情况下:1)更常用的是与that从句连用a)I think he is an excellent choice.b)We believe she is innocent.2)To be 可以省略a)I think him an excellent choice.b)We believe her innocent.3)可改为被动结构a)She is believed ( to be)innocent.b)He is thought (to be) an excellent choice.六、用作定语不定式作定语,通常至于他所修饰的名词或代词之后。
不过,不是任何名词都可用不定式作后置定语。
能这样用的名词一般和不定式之间存在这特定的关系,这样的名词通常是:1.相关动词的同源名词。
a)I don’t wish to change-----I have no wish to change.b)He refused to cooperate-----his refusal to cooperate annoyed everybody in the office.2.是与动词不定式连用的形容词的同源名词。
这样的名词有:ability, ambition, anxiety, eagerness,inclination, reluctance等。
a)The child has all eagerness to go on the picnic.b)Her reluctance to accept his invitation upset him.3.其他普通名词。
1)这时动词不定式常用来表达要对某事物作什么或将来产生什么影响。
a)Have you got a key to unlock this door?b)I need a box to hold my chessmen.2)二者还存在动宾关系,即所修饰的名词在逻辑上作不定式的宾语或不定式短语中的介词的宾语。
a)I gave the kid a book to read.b)I need a piece of paper to write on.如同前面说过的“形容词+不定式”需要注意:A)不定式动词后不能再加宾语a)I gave the kid a book to read it.*b)I need something to eat it.*B)不定式动词后介词不能省略a)I have no partner to speak english .*b)I need a pen to write.4.此外,被only, last, next, 序数词及形容词最高级修饰的名词常用不定式作定语。
a)I don’t think he is the best man to do the job.b)The next train to arrive is from New York.七、用作状语动词不定式作状语,主要表示目的、结果、原因、条件。
句子主语和不定式逻辑主语常一致或由“介词for+名词或代词”引出不定式的逻辑主语。
否则句子会因为不定式的逻辑主语不明确而显得不规范。
a)To study English well, a lot of practices are needed.(*)b) A lot of practices are needed to study English well.(*)应该这么说:a)To study English well, you need a lot of practices.b) A lot of practices are needed for you to study English well.1.用作目的状语注意三点:1)通常放在句子中间或句末。
a)I got a job on the side to earn money for my study.b)We had better start early to catch the train.2)若要强调目的状语,我们可有两种选择:一是在to前加上in order 或so as.a)I got a job on the side in order to earn money for my study.b)We had better start early so as to catch the train.二是把to do或in order to do 提到句首,此时注意:so as to 一般不用于句首。