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动词不定式(The Infinitive)
动词不定式：(to) + do,具有名词、形容词、副词的特征。
一、 不定式的形式：
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 bee n doing /
否定式： not /n ever + (to) do
二、 不定式的句法功能：
1•作主语：
eg.)To make a speech here is an honor.
To lose heart means failure.
动词不定式短语作主语时，常用形式主语 it作形式主语，如上两句可用如下形式：
It is an honor to make a speech here.
It means failure to lose heart.
常用结构：
It+be+ adj./n.+ for sb. to do sth.
It+be+ adj. + of sb. to do sth. =sb. be + adj. + to do sth.
(常见形容词 :clever, silly, foolish, stupid, wise, kind, rude, impolite, careless, cruel, crazy, etc.)
Eg.)It ' s necessary for us to have a good knowledge of English.
It is foolish of you to make such a mistake.=You are foolish to make such a mistake.
2. 作表语：
eg.)Her wish is to become a no velist.
He appears to have caught a cold.
不定式一般紧跟在系动词如 be, seem, rema in,即pear等后面，用来说明主语的内容。这类结构中的主语一般为名词，如:
idea, purpose, hope, pla n, inten ti on, wish, dream, etc.
eg.) My purpose is to teach them a less on.
有时句子主语也可以是不定式或名词性从句。
Eg.) To be strict with stude nts is to be resp on sible to them.
What I want to do is (to )tell you the truth.
如果主语中含有do的任何形式，那么不定式可以省去 to.
Eg.) The only thing he could do was ( to) tell the truth.
比较：
A组：Sth.+be +不定式(作表语)---表示主语的具体内容
Sth.+be +不定式(作表语)---表示时态(将来时