If的用法论文 篇1
Ⅰ、if引导条件状语从句的时候, 译为“如果, 假如”, 主句用将来时, 从句用一般时。
I'll go there if it's fine.如果天气晴朗, 我就去那里。
I won't go home if it rains tomorrow.如果明天下雨我就不回家。
Ⅱ、“祈使句+or+简单句”可转换为:“if引导的否定的条件句+主句”的句型, “祈使句+and+简单句”可转换为“if引导的肯定句+主句”的句型。
Be brave, or you'll lose your chance.
If you aren't brave, you'll lose your chance.
Come on, or we'll miss the early bus.
If we don't harry, we'll miss the early bus.
Ⅲ、If引导宾语从句时, 译为“是否”, 主句是一般现在时, 宾语从句可以用任何时态。
I don't know if it______ (rain) tomorrow, if it______ (rain) , I won't go there.
A、will rain;rains B、will rain, will rain
C、rains, will rain D、rains rains
正确答案选A, 前一个“if”引导的是宾语从句, 译为“是否”, 根据题意, 应用一般将来时;后一个“if”引导的条件状语从句, 译为“如果”, 主将从现。 (主句用一般将来时, 从句用一般现在时)
Ⅳ、“祈使句+if+从句”
Please tell me______you know the answer to the question.
A.if; B.so; C.but; D.because。
Please visit it______you have time
A.if; B.so; C.but; D.because。
析:两例答案都选A, 在两个例句中, 其结构“祈使句+if+从句”
You can buy some food in the supermarket if you are hungry.
Whether和if的用法比较 篇2
一般情况下,if 和 whether 均可引导动词后的宾语从句,常可以互换,如:
He asked me whether /if we wanted a drink.
I don’t know whether/if I can help you.
He didn’t know whether/if she was a nurse
I wonder whether/if you can examine him now.
They don’t care a bit whether/if my reports are good or bad..
但在decide,discuss后用whether不用if。如:
The committee are discussing whether he can join the Party.
The old lady has not decided whether she will live with her daughter in the countryside.
当使用 if 会引起歧义时应用 whether, 如:
Please let me know whether you want to go.(如换成if则既可看成条件从句又可看做宾语从句)
宾语从句前置时只能用 whether, 如:
Whether he lives there,I want to know.
Whether this is true or not ,I can’t say.
Whether we can relly help you ,I don’t know yet .我们是否真的能帮助你,我还不知道。
另外,whether 引导的从句的谓语动词不能用否定形式,但 if 引导的从句的谓语可以用否定形式,如:
I don’t care whether it doesn’t rain.(错)
I don’t care if it doesn’t rain.(正确)
介词后只能用 whether,不能用 if ,如:
I’m interested in whether you’ve finished the work.
There was a big argument about whether we should move to a new house.关于我们是否应搬新家发生了激烈的争论。
It depends on whether the letter arrives in time.这取决于信是否来得及时。
在带 to 的不定式前只能用whether,不能用 if,如:
I can’t decide whether to get marrried now or wait.我不能决定是该现在就结婚还是等待。
She hasn’t decided whether to go or not.她还没决定去还是不去。
在引导主语从句,表语从句和同位语从句时,一般只能用wheher 不用if,如:
Whether he’ll attend the meeting is unknown.
Whether they win or lose is all the same to me.
Whether it will do us harm or good remains to be seen.
但是,当采用形式主语it,而将主语从句后置时,用whether 和 if均可(尽管 whether 更常用):
It makes no difference to me whether/if it’s foggy or clear.
It’s not clear to me whether/if she likes the present.
The question is whether the man can be trusted.
The question is whether they can cooperate with us.问题是他们能否与我们合作。
The question whether he should come himself or send a substitute must be decided upon.他该亲自来还是派人替他来,这个问题必须定下来。
We will soon discuss the problem whether we should take some effective measures to protect the animals and plants in our region.我们很快将讨论是否应该采取一些有效措施来保护本地区的动植物这一问题。
Have you discussed the question whether you have enough time to do the work?你们有没有讨论过是否有足够的时间来做这项工作?
当用 or 提出两种选择时,whether 更常用,尤其是在正式文体中,如:
I don’t know whether I should go away or stay here.
Whether they do it or not matters little to us.他们干还是不干,与我们关系都不大。
What I want to know is whether the professor will come here or not next week.我想知道的是教授下周还来不来。
The little girl asked her father whether she should go to the party or not .女孩问父亲她应不应该参加这个晚会。
I don’t know whether it is raining or not .
但是,随着语言的发展,if 与 or,or not 也已为人们所接受,例如:
He didn’t know whether /if we should write or phone.(《最新牛津现代高级英汉汉英双解词典》)
How can you tell if the charge is positive or negative?你怎么知道电荷是正的还是负的?(《英汉技术词典》)
I wonder if /whether he is at home (or not ).(Harold E.Palmer:A Grammar of English Words)
I don’t care if/whether you car breaks down or not .(Geoffrey Jan Svartvik:A Communicative Grammar of English )
Let me know whether/if you can come or not .(Michael Swan: Practical English Usage)
然而,直接与 or not 连用时,则只能用 whether ,换句话说,只有 whether or not ,没有 if or not,如:Let me know whether or not you can come.告诉我你来还是不来。I wonder whether it is or not big enough.我不知道它是否够大。
以上是 if 和whether表示“是否”之意时的用法区别。此外,if 还有“假如”之意,引起条件状语从句;而 whether 另有“不管,无论”之意,引起让步状语从句。如:
If you want to learn a muscial instrument, you have to practice.如果你想学习一种乐器,你得练习它。You may leave the table if you have finished eating.你要是吃饱了,就可以离席了。
Whether it rains or not,we’ll go camping.无论下不下雨,我们都要去野营。
as if的用法总结 篇3
as if
犹如，好似
短语
as thoughas if 仿佛
as-if principle 实际原则
as s if 好像 ; 好象 ; 似乎
as-if hypothesis 似是假设
As-If God 类如上帝
As shocksome if you 像你如此夸姣的一私人
as-if personality 假想人格 ; 似是个性
As Though If Light 仿佛若光
as-if-infinity 无极限的
词语辨析
if only, only if, as if, even ifif only 但愿，希望，标示一种强烈的愿望，后接虚拟语气
only if 只有在……的时候，表示对条件的强调
as if 好像，仿佛，表比较
even if 及时，表让步
as if 的用法
一、as if 从句的作用
1. 在look, seem 等系动词后引导表语从句。如： She looks as if she were ten years younger. 她看起来好像年轻了十岁。 It seems as if our team is going to win. 看来我们队要胜了。
2. 引导方式状语从句。如： She loves the boy as if she were his mother. 她爱这男孩，就好像她是他的母亲一样。 The child talked to us as if he were a grown?up. 那孩子跟我们谈起话来，像个成年人似的。
二、as if 还可用于省略句中 如果as if 引导的从句是“主语+系动词”结构，可省略主语和系动词，这样as if 后就只剩下名词、不定式、形容词(短语)、介词短语或分词。
如： He acts as if (he was) a fool.
他做事像个傻子。
Tom raised his hands as if (he was going) to say something.
汤姆举起手好像要说什么。
She left the room hurriedly as if (she was)angry.
她匆忙离开房间好像生气的样子。
三、as if 从句的语气及时态
1. as if 从句用陈述语气的情况。 当说话者认为句子所述的是真实的或极有可能发生或存在的事实时。如： It sounds as if it is raining. 听起来像是在下雨。 He talks as if he is drunk. 从他谈话的样子来看他是醉了。
2. as if 从句用虚拟语气的情况。 当说话人认为句子所述的是不真实的或极少有可能发生或存在的情况时。从句虚拟语气动词时态的形式如下：
(1)如果从句表示与现在事实相反，谓语动词用一般过去时。
如： You look as if you didn’ t care.
你看上去好像并不在乎。
He talks as if he knew where she was.
他说话的样子，好像他知道她在哪里似的。
(2)从句表示与过去事实相反，谓语动词用“had+过去分词”。
如： He talks about Rome as if he had been there before.
他说起罗马来好像他以前去过罗马似的。
The girl listened as if she had been turned to stone.
那女孩倾听着，一动也不动，像已经变成了石头似的。
(3)从句表示与将来事实相反，谓语动词用“would/could/might+动词原形”。
如： He opened his mouth as if he would say something.
他张开嘴好像要说什么。
It looks as if it might snow.