动词不定式由to+动词原形构成。这里的to是不定式标志，没有词义。不定式具有名词、形容词或副词的某些语法功能，又有动词的时态和语态的特点及作用。
常见的形式如表所示（以及物动词do为例），不及物动词没有被动语态。
|
时态\语态 |
主动 |
被动 |
|
一般式 |
to do |
to be done |
|
进行式 |
to be doing |
/ |
|
完成式 |
to have done |
to have been done |
|
完成进行式 |
to have been doing |
/ |
有些动词可以用不定式作宾语，大致上有三种情况。
1）有些及物动词用不定式作宾语，结构为动词+不定式。
|
afford |
aim |
agree |
arrange |
ask |
decide |
|
bother |
care |
choose |
demand |
desire |
determine |
|
elect |
endeavor |
hope |
fail |
help |
learn |
|
long 渴望 |
mean |
manage |
offer |
plan |
pretend |
|
refuse |
tend |
undertake |
expect |
hate |
intend |
例如：
The driver failed to see the other car in time. 司机没能及时看见另一辆车。
He offered to help me. 他表示愿意帮助我。
2）有些动词除了可以用不定式作宾语，还用不定式作补语，即有动词+宾语+不定式的结构。
|
ask |
choose |
expect |
help |
beg |
intend |
|
like/love |
need |
prefer |
prepare |
want |
wish |
例如：
I like to keep everything tidy. 我喜欢每件东西都保持整洁。
I like you to keep everything tidy. 我喜欢你使每件东西都保持整洁。
I want to speak to Tom. 我想和汤姆谈话。
I want you to speak to Tom. 我想让你和汤姆谈话。
3）有些动词或动词词组可以用动词+疑问词+不定式的结构作宾语。
|
decide |
know |
consider |
forget |
learn |
remember |
|
show, |
wonder |
find out |
tell |
inquire |
explain |
例如：
Please show us how to do that. 请演示给我们如何去做。
There are so many kinds of tape-recorders on sale that I can't make up my mind which to buy.
有这么多的录音机，我都拿不定主意买哪一种。
不定式作补语
1） 有些有动词+宾语+不定式的结构。
|
advise |
allow |
cause |
challenge |
command |
compel |
|
drive 驱使 |
enable |
encourage |
forbid |
force |
impel |
|
induce |
instruct |
invite |
like/love |
order |
permit |
|
make |
let |
have |
want |
get |
warn |
|
persuade |
request |
send |
tell |
train |
urge |
例如；
Father will not allow us to play on the street. 父亲不让我们在街上玩耍。
The officer ordered his men to fire. 长官命令士兵开火。
注意：有些动词如make，have，get，want等可用不定式作做宾补，也可用分词作宾补。现在分词表达主动，也表达正在进行，过去分词表达被动。
2) 有些有动词+宾语+不定式的结构，不定式的动词往往是be，不定式一般可以省去。
|
consider |
find |
believe |
think |
declare（声称） |
appoint |
|
guess |
fancy（设想） |
guess |
judge |
imagine |
know |
例如：
We believe him to be guilty. 我们相信他是有罪的。
We know him to be a fool. 我们知道他是个笨蛋。（to be 不能省去）
3) 有些动词可以跟there +to be的结构。
|
believe |
expect |
intend |
like |
love |
mean |
|
prefer |
want |
wish |
understand |
|
|
例如：
We didn't expect there to be so many people there. 我们没料到会有那么多人在那里。
You wouldn’t want there to be another war. 你不至于想让另外一场战争发生吧。
不定式作主语
不定式作主语，往往用it作形式主语，真正的主语不定式放至句子的后面。
例如：It's so nice to hear your voice. 听到你的声音真高兴。
It's necessary for you to lock the car when you do not use it. 不用车的时候，锁车是有必要的。
It's very kind of you to help us. 他帮助我们，他真好。
It seemed selfish of him not to give them anything. 他不给他们任何东西，这显得太自私了。
但是，用不定式作主语的句子中还有一个不定式作表语时，不能用It is… to…的句型。另外，这样的句子，不能用动名词作表语。例如：
（对）To teach is to learn.
（错）It is to learn to teach.
（错）To teach is learning.
（错）Teaching is to learn.
It's for sb.和 It's of sb.
这样的句子中，由于表语形容词性质的不同，导致了不定式逻辑主语标志用for或of的区别。
1） for sb. 句型中的形容词一般为表示事物的特征特点，表示客观形式的形容词，如easy, hard, difficult, interesting, impossible等：例如：
It's very hard for him to study two languages. 对他来说学两门外语是很难的。
2）of sb句型中的形容词一般为表示性格，品德，心智能力，表示主观感情或态度的形容词，如good, kind, nice, clever, foolish, right。例如：
It's very nice of you to help me. 你来帮助我，你真是太好了。
用for还是用of 的另一种辨别方法：
用介词for或of后面的逻辑主语作句子的主语，用介词前边的形容词作表语，造个句子。如果通顺用of，不通则用for。例如：
You are nice. （通顺，所以应用of）。
He is hard. （非所表达的意思，不通，因此用for。）
今日练习题：
1．Charles Babbage is generally considered ___ the first computer.
A. to invent B. inventing C. to have invented D. having invented
2．The chair looks rather hard, but in fact it is very comfortable to ___.
A. sit B. sit on C. be seat D. be sat on
3．It seems impossible ______ across this wide river.
A. swim B. swimming C. to swim D. to be swam
4．It was foolish __________ him.
A. for her to believe B. of her to believe C. for her believing D. to her believe
5．There are several ______ leaves on the ground.
A. falling B. fallen C. to fall D. fell
答案回复可见（如果您的回复能加上分析，对知识点印象会更深刻，另外我们也将给予更多的奖励。）
本帖隐藏的内容需要回复才可以浏览
