形式主语it的用法
it 作形式主语主要用于下列三种情况（详细情况点此链接http://baike.baidu.com/view/954899.htm）
不定式作真正主语
主要用于下列句型： 1. It + is/was + adj./n. (形容词或名词) +to do sth. 名词从句作真正主语
用it 作形式主语的结构主要用于下列句型： It +谓语+名词从句(主语从句、表语从句、同位语从句) 1. It is +名词+从句: 这样的名词有a fact, a surprise, an honor(非常荣幸),a pity, common knowledge(常识)等。例如： It is common knowledge that the full moon brings fair weather. 皓月兆天晴,这是常识。 It is a surprise that you gave such an answer to the question. 你对这个问题作了这样的回答，令人吃惊。 2. It is +形容词+从句: 这样的形容词有natural, true, strange, necessary, important, obvious(很明显), certain, wonderful, funny, possible, likely, probable等。例如： It is certain that free medical care will be given to most people in our city. 我们城市的多数人将享受免费医疗，这是一定的。 It is probable that he has known everything. 很可能他什么都已经知道了。 3. It +动词+从句: 这样的动词有seem,happen, appear, look, matter, make, strike, occur(突然想起)等。 It appeared that he had a taste for music. 看来他对音乐有一定的鉴赏力。 It made us very happy that she was saved.她能化险为夷令我们大家很高兴。 4. It + be + 分词+从句: 这样的分词有 said(据说)， reported(据报道),believed(人们相信)，known(众所周知)，decided(已决定)，proved(已证实), thought, expected, annouced, arranged, amusing, puzzling, striking等。例如： It is said that Li Hao has been to Europe.据说李郝去过欧洲。 It was amusing that a rabbit ran out of the empty box on the desk.桌上的空盒子里竟然跑出来一只兔子,太有趣了。 需要说明的是，大部分连接词引导的主语从句都可以用 it充当形式主语。例如： It remains unknown when they are going to get married. 他们何时结婚依然不明。 It says in the newspaper that the enemy has been defeated. 报纸上报导敌人被打败了。 形式主语： It +be+(the)+adj.+for sb.+to do sth.
如：It is very kind of you to give me a hand in time.It is my pleasure to address the meeting.It was pretty hard for him to bring up the child on his own. 如：It so happened that the tickets were sold out.It is extremely obvious that she has been lying about her identity.It suddenly occurred to me that the message must have been hiddenbetween the layers of the briefcase. 这类句子远不如前面两种出现率高，主要在（no good,waste,useless,no use,dangerous）等词语的后面用如：It is no use reasoning with him.It is no good reading in dim light.作形式主语的代词只能用it ，不能用that，this等词。例如:1） It is easier to lose friends than to make friends. 交朋友难而失去朋友比较容易。2） It is important for modern young people to master at least two foreign languages. 掌握至少两门外语对于当代年轻人来说是很重要的。以上两句中的it是形式主语，真正的主语是后面的不定式短语。3） It is considered no good reciting without understanding. 不理解的背诵被认为是没有好处的。4） It is no use crying over spilt milk. 覆水难收。以上两句中的it是形式主语，真正的主语是V-ing形式。5） It is a fact that English is being accepted as an international language.英语作为一门国际语言正日益为人们所接受，这是不争的事实。（NMET,95）6） It depends on the weather whether we will go. 我们去不去得看天气行事。（其中的whether 不能换成if，因为if不能引导主语从句。）以上两句中真正的主语是名词性从句。
作形式主语常见句型
1.It + be +
形容词
+ that-
从句
可用于此句型的形容词有
: wonderful, true
，
good
，
right
，
wrong
，
（
un
）
important
，
useless
，
surprising
，
disturbing,frightening,alarming,clear
，
unusual
，
lucky
，
certain, necessary
等。
如：
①
It is quite certain that he will be at the meeting.
他将出席会议是无疑的。
②
It is surprising that he came late to school this morning.
他今天早上迟到真令人惊讶。
③
It is important that we (should) study hard.
我们努力学习是很重要的。
注意
:
该句型中的形容词是
（
un
）
important, necessary
等时，
从句应为
(should )+
动词原
形。
It is important that we (should) learn English well.
It is necessary that he (should) remember these words.
2.It + be +
名词
+ that-
从句
适用该句型的名词
（词组）
有
: a pity
，
an honor
，
a good thing
，
a fact
，
a surprise
，
a question,
a shame,a custom, a truth,our hope, no wonder, good/bad manners
等。如：
①
It is a pity (that) you missed the sports meeting last week.
你错过了上周的运动会太
可惜了。
②
It is a fact that English is being accepted as an international language.
事实上英语已经
被作为一种国际语言而接受了。
3. It
＋
seem
／
appear
／
happen
的适当形式＋
that
从句。
①
It seems that there is a big waste pipe coming down from the town.
②
It appeared that he was calm, but inside his heart was beating wildly with fear.
4. It + be +
过去分词
+
主语从句，这类过去分词有：
announced, believed, expected, hoped,
decided, reported, said, shown
等，
如：
It is reported that 16 people were killed in the earthquake.
It is not decided who will give the operation to the patient.
5. It is time ( about time ,high time ) that ...
该句型中
that
后的从句应该用虚拟语气，值得注意的是①
常用过去时态表示虚拟．②
有时也用
should +
动词原形，
should
不能省。常译为＂是（正是）
．
．
．的时侯．
．
．＂。
It is time that children should go to bed.
= It is time that children went to bed.
6. It is the first ( second ... ) time that ...
用完成时态。至于用什么完成时态，
由主句的谓语动词的时态决定。如果是一般现在时，后
面从句用现在完成时态；
如果是一般过去时，
后面从句则用过去完成时态。
该结构中
that
可
以省去；
it
有时用
this
替换．常译为＂是第一（二）
．
．
．次．
．
．＂。
It is the first time I have been here.
= This is the first time I have been here.
7. It + be + adj./ n. (for sb. / of sb.) + to do sth.
该句型中的形容词通常是表示事物的特点或
特征的如
difficult
，
hard
，
easy
，
impossible
，
necessary
，
important
等，此时用
for
；或表示人
的性格特征或特点的如
nice
，
good
，
bad
，
kind
，
silly
，
foolish
，
wise
，
clever
，
careless
，
rude
，
brave
，
cruel
，
careful
，
grateful
等，这时要用
of
。如：
①
It is foolish of you to give up such a good chance.
②
It is necessary for college students to master at least a foreign language.
当代英语通常用it 做形式主语定式和动名词置于谓语面特别主语较长时或些习惯用法
1） 谓语系表结构（be + 形容词 / 名词）时常定式置构成句型 it + be + 表语（形容词 / 名词）+ 定式
例 1 It is my duty to care for that patient.
照料位病人我职责（做主语定式to care for that patient 置it 形式主语）
例 2 It is not an easy thing to master a foreign language.
掌握门外语件容易事
例 3 It isn’t right to speak ill of someone behind his back.
别人背说坏对
2） 当谓语 takemakepaycost require feelneed 等动词时或者与情绪有关动词 delightamuseexciteannoyirritate 等时习惯上常用 it 做形式主语并定式置
例 1 It takes only ten minutes to get there.
儿只需十分钟
例 2 It pays to be honest.
诚实会吃亏
例 3 It feels good to stay away from the crowded city.
能远离拥挤城市感觉真错
例 4 It annoyed her to see someone spit on the ground.
看见有人随地吐痰让生气
3） 同定式样动名词也用于it + be + 表语 + 动名词句型二者区别参见10．2．2 1）论述下面两组句子没有多大差异
例 1 A） It is a waste of time to argue with him
B） It is a waste of time arguing with him.
和争辩浪费时间
例 2 A） It is worthwhile to discuss this again.
B） It is worthwhile discussing this again.
点值得讨论下
4） 表语（of）no usenot any usenot the slightest use no good not much goodfun等时常用动名词（用定式）做主语并置用 it 做形式主语
例 It’s no use crying over spilt milk.
覆水难收
5） 动名词还 there be 句型做主语（能用定式）常见形式 there is no + 动名词或 there is no / any + 名词 + 动名词
例 1 There is no denying the fact.
事实无否定
例 2 There isn’t any use trying again.
再试也没用
以调制出不同的风味来,这是最简单的烹饪常识.比如丈夫在妻子生日那天献上一束水灵的玫瑰花儿,在妻子的腮边印上甜蜜吻痕的同时,再对妻子说：“老婆,我爱你”于是从妻子嘴角边遗漏出带有皱纹如同少女般的嗔怪：“去,怎么还这么肉麻”的表情里,再品味一次年轻时初恋的情怀.以至能够信心十足着进行完美爱情的接力赛,彼此相携到老.有了这样完美的爱情,我想即使有一天,两个人伫立站黄昏的夕阳下,戴着沧桑的老花镜,咀嚼着岁月的牙齿,仍能品出完美爱情那香喷喷的味道来!
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爱情没有谁会等谁一辈子
爱情没有谁会等一辈子,别失去才后悔……
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