e.g: To finish the building in a month is difficult.
To do such things is foolish.
To see is to believe. (对等)
注: 1). 不定式作主语时,谓语用单数
2). 当主语较长,谓语较短时,常用it做形式主语,而将不定式放到谓语的后面。
it做形式主语,不定式放在谓语动词之后常用于下列结构中:
(1)It is/was +adj.+of sb. to do…
(2) It is +adj.+for sb.+to do…
It is easy / difficult / hard / foolish / unwise / right / wrong / unnecessary
(3) it is +a +名词+ to do...
It is a pity / a pleasure / a pleasant thing / one’s duty / an honor / a shame / a crime / no easy job… to do
It takes (sb.) some time / courage / patience …to do…
It requires courage / patience / hard work… to do…
注意: probable 和 possible 均可作表语,但possible可以用不定式作真实主语, 而probable不能用不定式作真实主语。
It is probable for him to come to the meeting.(错)
It is possible for him to come to the meeting.
It is possible / probable that he will come to the meeting.
英语高考必背知识要点二
一、非谓语动词
“非谓语动词”可分为动词不定式、动名词和分词.它在 句子 中的作用很多:除了不作谓语外,它可以充当主语、宾语、表语、定语、状语与复合宾语(主语补语或宾语补语).有些及物动词后面接不带to的不定式作复合宾语.这些动词归纳如下:一感(feel).二听(hear,listen to),三让(have,1et, make),四看(see,watCh,notice,observe).再加上help somebody(to)do something和美国英语look at somebody do somthing.还有“二让”属特殊:get somebody to do something 与keep somebody doing.而有些及物动词后面接动名词(the -ing form)作宾语.这些动词归纳为一句话:Papa C makes friends.这是由如下动词的开头字母组成:permit,advise, practise,avoid,consider,mind, allow,keep,enjoy,suggest, finish,risk,imagine,escape,need,delay,stand(忍受). 为了容易记住,也可以编成 顺口溜 :“允许完成练习,建议避免冒险,考虑延期逃跑,喜欢保持想象,需要反对忍受”.其相对应的动词依次是:permit/allow,finish,practise;