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1. (表示条件)如果 ,主句用将来时，if从句用现在时表示将来
He will come if you invite him.
如果你请他,他会来的。
2. (表示虚拟)假如,要是
1）时态：可以表示过去，现在和将来的情况。它的基本特点是时态退后。
a. 同现在事实相反的假设。
句型 ： 条件从句 主句
一般过去时 should( would) +动词原形
If they were here, they would help you.
b. 表示于过去事实相反的假设。
句型： 条件从句 主句
过去完成时 should(would) have+ 过去分词
If she had worked harder, she would have succeeded.
The rice would not have been burnt if you had been more careful.
If my lawyer had been here last Saturday, he would have prevented me from going.
If he had come yesterday, I should / would have told him about it.
含义：He did not come yesterday, so I did not tell him about it.
If he had not been ill and missed many classes, he would have made greater progress.
含义： He was ill and missed many lessons, so he did not make greater progress.
c. 表示对将来的假想
句型： 条件从句 主句
一般过去时 should+ 动词原形
were+ 不定式 would + 动词原形
should+ 动词原形
If you succeeded, everything would be all right.
If you should succeed, everything would be all right.
If you were to succeed, everything would be all right.
3. 是否 = whether 连接宾语从句
I wonder if she is ill.
不知她是否病了。
ardim-
IF的用法
if是英语中出现频率很高的连词，并且它的用法也很多。学生感到很难掌握，为了让同学们更多更好地了解其用法及其语法功能。现结合教学中遇到的情况，予以归纳，以供参考。
一、if作为连词，引导条件状语从句，它表示的意思是“假如”“如果”等。在复合句中如果主句用将
来时，则if引导的状语从句用一般现在时。例如：
1. If itdoesn"train, we will go to the park next Sunday. 如果天不下雨，下周星期天我们将去公园。
2. If you ask him，he will help you．如果你求他，他将会帮助你。
二、if还可以引导让步状语从句。这时if当作“即使是”，“虽说”解。例如：
1. If she"s poor，at least she"s honest． 虽说她很穷，但至少她还是诚实的。
2. If I am wrong，you are wrong， too． 即使说我错了，那么你也不对。
3. I"ll do it, even if it takes me all the afternoon． 虽然会花费我一下午的时间，我还是要做这事。
三、if作为连词还可以引导宾语从句。引导宾语从句时和whether意思相同。例如：
1. Lily asked if ／ whether she liked it. 莉莉问她是否喜欢它。
2. She asked if ／ whether they had a cotton one． 她问是否他们有一件棉织的。
四、if引导时间状语从句，当if做“当”或“无论何时”解而不含有条件之义时，if从句中的时态与主句中的时态相同。例如：
1. If youmix yellow and blue，you get green．你将黄色与蓝色混合，便会得到绿色。
2. If she wants the servant，she rings the bell．每当她需要仆人时，她便按铃。
五、if后接否定动词，用于感叹句中，表示沮丧、惊奇等。例如：
I. Well，if I haven"t left my false teeth at home!真倒霉，我把假牙丢在家里了!
2. And if he didn"t try to knock me down!(What do you think he did!He tried knock me down!)你猜他想做什么?他想把我撞倒!
六、用于虚拟语气中，if从句中用过去式，表示不可能实现，大概不会实现或提出作为考虑的假定条件。例如：
1. If you were a bird, you could fly.假使你是只鸟，你便会飞了。
2. If I asked him(if I were to ask him) for a loan，would he agree?如果我向他借贷，他会答应吗?
另外，if从句中用过去完成式，表示过去未实现的条件(例如由于不可能实现或某人之未能实行)。例如：
1. If they had startedearlier，they would have arrivedin time．要是他们早些动身，他们便可及时到达了。
2. If they had not started when they did，they would not be here now．如果他们那时不动身，现在他们就不会在此地了。
第三，在文学体栽中，if有时可省略，然后将主语与所用的限定动词(尤其是were，had，should)倒置。例如：
1. Should it (=if it should)be necessary，I will go. 倘若有必要，我会去的。
2. Were I(=if I were) in your place，I would do the same ． 如果我处于你的位置，我也会这样干的。
3. Had I(=if I had)known earlier，I would come．如果我早一点知道，我就会来。
七、if与其它一些介词的连用。
首先，as与if连用，它的意思是：“仿佛、好像”同样引导从句。例如：
1. It isn"t as if we are rich．(We are not rich．)我们不像富有的样子。(即我们不富有)
2. It isn"t as if he doesn"t know the ruler．(i．e．He does know the rulers．)他不像不懂规则的样子。(即他懂得规则)
另外as if还可以引导感叹句。例如：
As if I would allow it!(i．e．I would certainly not allow it!)好像我会答应似的!(我才不会答应哩!)
其次, if与only连用。常表示愿望或一个未实现的条件，尤其用于感叹句中。例如：
1. If only he arrives in time!他若能及时到达就好了!
2. If only she would marry me!但愿她能嫁给我！
3. If only she had known about it!（But she didn"t know.） 她那时要是知道（但她不知道）这事就好了!
CarieVinne-
if
if
[If; if]
连接词
A
1 如果…,假使…
a. [就现在、过去、未来可能实现之事加以推测时]
If you are tired, we will go straight home.
如果你疲倦了,我们就直接回家
If you have finished reading this book, please return it to me.
如果你念完这本书,请把它还给我
If he did it, he committed a crime.
如果他做了那件事,他就犯了罪
I"ll be hanged [damned] if I obey him. (
口语)我才不会听他的话
Do you mind if I open the window?.
如果我打开窗子,你介意吗?
(我可以打开窗子吗? )
I shall tell him if he comes.
如果他来了,我会告诉他
b.
If you knew how I suffered, you would pity me.
如果你知道我多么受苦,你会同情我
If I were you, I would help him.
如果我是你,我会帮助他
c.
If I had known, I wouldn"t have done it.
假使我知道,我就不会做那件事
If he had followed my advice, he wouldn"t be in such difficulty now.
如果他听从我的劝告,他现在就不会陷入如此的困境
d.
If it should rain tomorrow, I shall not [shan"t, won"t] come.
万一明天下雨,我就不来
e.
If I were to die tomorrow, what would you do?.
要是我明天死了,你怎么办?
2 a. 即使… (even though)
If he be ever so rich.
?.(古)即使他很富有…
If I am wrong, you are not absolutely right.
即使我错,你也不一定绝对正确
He is a good if mischievous boy.
即使他再顽皮,还是个好孩子
His manner, if patronizing, was not unkind.
他的态度即使有点傲慢,也不能说是不和善
I don"t care if I go. (
口语)我可以去; 我去也可以
(对于邀请的肯定回答)
→ even if,if not.
b. 即使…,然而… (whereas)
If he was not industrious in his youth, he now works very hard.
诚然,他年轻的时候不勤奋,然而现在他工作很卖力
3 每逢…时,不论何时 (whenever)
If I feel any doubt,I ask.
每逢有疑问时我就发问
4 [省略结论的主句,单独用作表示惊叹、愿望等的感叹句]
If I only knew! =If only I knew!.
要是我知道的话该多好!
If I haven"t lost my watch!.
要是没丢掉表该多好!
(该死,丢了表!)
Why, if it isn"t Mr. Smith!.
嗨,那不正是史密斯先生!
B [引导间接疑问句] 是不是… (whether)
Ask him if it is true.
问他那是不是真的
I wonder if he is in the school.
我不知道他是否在学校
as if → as
even if
即使
Even if you do not like it, you must do it.
即使你不喜欢那件事,你也得去做
if a day [an inch,a penny,etc.]
一天 [一??一便士] 不少,确实,至少
He is seventy if a day. (.
一天也不差) 他确实有七十岁
The enemy is 2000 strong, if a man. (.
一个也不少) 敌军至少有两千人
He measures six feet, if an inch. (.
一?家膊簧? 他至少有六?崭?nI have walked 15 miles, if a yard. (.
一码也不少) 我确实已走了十五哩
if any
即使有,如果有的话
There are few (books),if any.
即使有 (书) 也很少
There is little (wine), if any.
即使有 (葡萄酒) 也很少
Correct errors, if any.
如果有错误,即予以订正
if anything
要说有什么区别的话,甚至可能,说起来
Things are, if anything, improving.
事态甚至可能好转
True greatness has little, if anything, to do with rank and power.
说起来,真正的伟大与地位权力没什么关系
if anywhere
如有任何地方
if at all → at all
If it had not been for ?
如果没有…的话 (But for?)
If it had not been for.
? = Had it not been for your advice,I couldn"thave done it.如果没有你的忠告,我不可能完成那件事
If it were not for?
如果没有…的话 (But for?)
If it were not for (= Were it not for) the sun, nothing could live.
如果没有太阳的话,任何东西都不能生存
if necessary [possible]
如果有必要,如果可能
I will do so, if necessary.
如果有必要,我会这样做
if not
(1)即使不是…
It is highly desirable, if not essential, to draw the distinction.
即使非属必要,但仍然宜加以区别
(2)如果不是…
Where should I get stationery, if not at a department store ?.
如果不是在百货公司,我该在哪里买文具?
if only
(1)→ conj. A 4
(2)即使只…
We must respect him if only for his honesty [if only because he is honest].
即使只为了他的诚实,我们也必须尊敬他
I want to go if only to see his face.
光是为了见他一面,我也要去
if you like → like
if you please → please
What if?? →what pron
可数名词
(pl. ~s)
条件; 假设,假使
There are too many ifs in his speech.
他说话中有太多的“假使”
ifs and buts
事情延后的理由 [借口]
Do it now, and no ifs and buts!.
现在就做,不要尽找借口
snjk-
if
连接词 conj.
1.
(表示条件)如果
He will come if you invite him.
如果你请他,他会来的。
2.
(表示虚拟)假如,要是
If I were you, I would never do that.
如果我是你,我决不做那件事。
3.
(表示让步)即使
We"ll go even if it rains.
即使下雨我们也要去。
4.
是否
I wonder if she is ill.
不知她是否病了。
5.
(表示因果关系)每一次...的时候(总是会)
If I feel any doubt, I inquire.
我一感到有疑问就随时询问。
名词 n.
1.
条件;设想[C]
There are too many ifs in his offer.
他的提议中条件太多了。
tt白-
引导条件状语从句，意为：如果。从句多为一般现在时。二。引导宾语从句，意为：是否。从句时态根据主句时态而定。三。虚拟语气。意为：如果。从句多为一般