If引导的状语从句有几种用法，如何辨析？

请问if 引导的条件状语从句有几种形式~

状语从句：
用一个句子（从句）来作另一个句子（主句）的状语，用作状语的句子就叫作状语从句。作什么样的状语就叫什么类型的状语从句。例如：条件状语从句就是用一个句子来作条件状语。
状语从句的分类：
（1）时间状语从句
凡是从句都必须有引导词，引导时间状语从句的词有when，before，after，until，as soon as，while 等。
（2）条件状语从句
主要看一下由if引导的条件状语从句。if 意为“如果”，引导条件状语从句时，表示假如有从句的动作发生就（不）会有主句的动作发生。例如：
If it doesn't rain tomorrow，we will go there by bike.如果明天不下雨，我们就骑自行车去那里。
If I get there early，I can see the doctor quickly.如果我早早地到那里，我就可以快点看病。
3）地点状语从句用法要点
常用where（哪里）和wherever（无论哪里）eg.
Where there is a will，there is a way. 有志者，事竟成。
We will go wherever the motherland need us most. 我们要到祖国最需要的地方去。
（4）原因状语从句用法要点
常用的引导连词有because，as和since，三者的区别是：在回答问题的时候，使用because；对于显而易见的原因，常用as或since；as和since的从句常放在主句之前，而because的从句常放在主句之后。eg.
Why did you go？ I went because Tom told me to go. 你为何去？那是因为汤姆叫我去。
He was angry not because we were late but because we made a noise.
他很生气不是因为我们来迟了，而是因为我们弄出了声音。
As it was raining hard，we had to be indoors. 由于雨太大，我们只好呆在家里。
Since you feel ill，you'd better not go to work. 既然你感觉不舒服，你最好不要去上班了。
（5）目的状语从句用法要点
常用的引导连词有so that，that和in order that译为：以便，为了，目的是。eg.
Please speak more slowly so that we can make full notes. 请讲慢一点，以便我们能作详细笔记。
I shall write down your address that I may not forget. 我要把你的地址记下来，以免忘记。
I sent the letter by air mail in order that it might reach him in time. 这封信我以航空信发出，以便他能及时收到。
注：目的状语从句可以用动词不定式来替换做目的状语。eg.
We work harder than usual finish it in a week. 我们比平常加倍努力工作以在一周内完成工作。
三、主句与从句时态一致的问题。
在时间状语从句和条件状语从句中，主句和从句之间的时态一致问题一般分下列两种情况：
1. 若主句是祈使句，或主句中有情态动词，或主句中谓语动词是一般将来时，那么从句用一般现在时表示一般将来时。例如：
Be careful when you cross the road. 过马路时要小心。
Put up your hand if you have any questions to ask. 如果你们有问题要问的话，请举手。
The traffic must stop when the lights are red. 红灯亮时，车辆必须停下。
2. 若主从句谓语动词都是陈述过去，那么主从句都可以用一般过去时。例如：
She could sing when she was four years old. 她四岁的时候就会唱歌。

if 条件句不一般,几个要点记心间;
条件句,放在前,逗号要放句中间。
条件句表可能，主句多用将来时；
条件句表事实，主句常用现在时。

在 if 引导的条件状语从句中，如果从句谈论的是一个有可能发生的事实及其产生的相关的结果，主句用一般将来时态，从句用一般现在时态。如：
We can walk there if we can't find a bus .
If it rains tomorrow ,we will not go to the zoo.
What will you do if you find a panda in danger.
如果 if 条件句谈论的是重复发生和预示要发生的情景和事件，则主从句大多用一般现在时态。如：
If bears are in danger ,they attack people.


注意 ：
在 if 引导的条件状语从句中，if 和条件句位置灵活，可直接放在主句后面，若 if 条件句放句首，
从句后面要加逗号，和主句隔开。
还要注意前后时态一致原则

19. 状语从句

19.1 地点状语从句

地点状语从句通常由where, wherever 引导。

Where I live there are plenty of trees.
我住的地方树很多。
Wherever I am I will be thinking of you.
不管我在哪里我都会想到你。

19.2 方式状语从句

方式状语从句通常由as, (just) as…so…, as if, as though引导。

1） as, (just) as…so…引导的方式状语从句通常位于主句后，但在(just) as…so…结构中位于句首，这时as从句带有比喻的含义，意思是"正如…"，"就像"，多用于正式文体，例如：
Always do to the others as you would be done by.
你希望人家怎样待你，你就要怎样待人。

As water is to fish, so air is to man.
我们离不开空气，犹如鱼儿离不开水。

Just as we sweep our rooms, so we should sweep backward ideas from our minds.
正如打扫房屋一样，我们也要扫除我们头脑中落后的东西。

2） as if, as though
两者的意义和用法相同，引出的状语从句谓语多用虚拟语气，表示与事实相反，有时也用陈述语气，表示所说情况是事实或实现的可能性较大。汉译常作"仿佛……似的"，"好像……似的"，例如：

They completely ignore these facts as if (as though) they never existed.
他们完全忽略了这些事实，就仿佛它不存在似的。（与事实相反，谓语用虚拟语气。）

He looks as if (as though) he had been hit by lighting.
他那样子就像被雷击了似的。（与事实相反，谓语用虚拟语气。）

It looks as if the weather may pick up very soon.
看来天气很快就会好起来。（实现的可能性较大，谓语用陈述语气。）

说明：as if / as though也可以引导一个分词短语、不定式短语或无动词短语，例如：

He stared at me as if seeing me for first time.
他目不转睛地看着我，就像第一次看见我似的。

He cleared his throat as if to say something.
他清了清嗓子，像要说什么似的。

The waves dashed on the rocks as if in anger.
波涛冲击着岩石，好像很愤怒。

19.3 原因状语从句

比较：because, since, as和for

1） because语势最强，用来说明人所不知的原因，回答why提出的问题。当原因是显而易见的或已为人们所知，就用as或 since。
I didn't go, because I was afraid.
Since /As the weather is so bad, we have to delay our journey.

2） 由because引导的从句如果放在句末，且前面有逗 号，则可以用for来代替。但如果不是说明直接原因，而是多种情况加以推断，就只能用for。
He is absent today, because / for he is ill.
He must be ill, for he is absent today.

19.4 目的状语从句

表示目的状语的从句可以由that, so that, in order that, lest, for fear that, in case等词引导，例如：
You must speak louder so that /in order that you can be heard by all.
He wrote the name down for fear that(lest) he should forget it.
Better take more clothes in case the weather is cold.

19.5 结果状语从句

结果状语从句常由so… that 或 such…that引导，掌握这两个句型，首先要了解so 和 such与其后的词的搭配规律。

比较：so和 such
其规律由so与such的不同词性决定。such 是形容词，修饰名词或名词词组，so 是副词，只能修饰形容词或副词。 so 还可与表示数量的形容词many, few, much, little连用，形成固定搭配。

so foolish such a fool
so nice a flower such a nice flower
so many / few flowers such nice flowers
so much / little money. such rapid progress
so many people such a lot of people
（ so many 已成固定搭配，a lot of 虽相当于 many，但 a lot of 为名词性的，只能用such搭配。）

so…that与such…that之间的转换既为 so与such之间的转换。
The boy is so young that he can't go to school.
He is such a young boy that he can't go to school

19.6 条件状语从句

连接词主要有 if, unless, as/so long as, on condition that 等。.
if 引导的条件句有真实条件句和非真实条件句两种。非真实条件句已在虚拟语气中阐述。

unless = if not.
Let's go out for a walk unless you are too tired.
If you are not too tied, let's go out for a walk.

典型例题
You will be late ___ you leave immediately.
A. unless B. until C. if D. or
答案A。 句意：除非你立即走，否则你就回迟到的。可转化为 If you dong leave immediately, you will be late. B、D句意不对，or表转折，句子如为 You leave immediately or you will be late.

19.7 让步状语从句

though, although
注意： 当有though, although时，后面的从句不能有but，但是 though 和yet可连用
Although it's raining, they are still working in the field.
虽然在下雨，但他们仍在地里干活。
He is very old, but he still works very hard.
虽然他很老，但仍然努力地工作。
Though the sore be healed, yet a scar may remain.
伤口虽愈合，但伤疤留下了。 （谚语）

典型例题
1） ___she is young, she knows quite a lot.
A. When B. However C. Although D. Unless
答案：C。意为虽然她很年轻，却知道许多。

2) as, though 引导的倒装句
as / though引导的让步从句必须表语或状语提前（形容词、副词、分词、实义动词提前）。
Child as /though he was, he knew what was the right thing to do.
= Though he was a small child, he knew what was the right thing to do.

注意： a. 句首名词不能带任何冠词。
b. 句首是实义动词，其他助动词放在主语后。如果实义动词有宾语和状语，随实义动词一起放在主语之前。
Try hard as he will, he never seems able to do the work satisfactorily.
= Though he tries hard, he never seems…
虽然他尽了努力，但他的工作总做的不尽人意。

3) ever if, even though. 即使
We'll make a trip even though the weather is bad.

4) whether…or- 不管……都
Whether you believe it or not, it is true.

5) "no matter +疑问词" 或"疑问词+后缀ever"
No matter what happened, he would not mind.
Whatever happened, he would not mind.
替换：no matter what = whatever
no matter who = whoever
no matter when = whenever
no matter where = wherever
no matter which = whichever
no matter how = however
注意：no matter 不能引导主语从句和宾语从句。
（错）No matter what you say is of no use now.
（对）Whatever you say is of no use now.
你现在说什么也没用了。(Whatever you say是主语从句)
（错）Prisoners have to eat no matter what they're given,
（对）Prisoners have to eat whatever they're given. 囚犯们只能给什么吃什么。

19.8 比较while, when, as

1）as, when 引导短暂性动作的动词。
Just as / Just when / When I stopped my car, a man came up to me.
2）当从句的动作发生于主句动作之前，只能用when 引导这个从句，不可用as 或 while。
When you have finished your work, you may have a rest.
3）从句表示"随时间推移"连词能用as，不用when 或while。
As the day went on, the weather got worse.
日子一天天过去，天气越变越坏。

19.9 比较until和till

此两个连词意义相同。肯定形式表示的意思是"做某事直至某时"，动词必须是延续性的。否定形式表达的意思是"直至某时才做某事"。动词为延续性或非延续性都可 以。 正确使用这两个连词的关键之一就在于判断句中的动词该用肯定式还是否定式。

肯定句：
I slept until midnight. 我一直睡到半夜时醒了。
Wait till I call you. 等着我叫你。
（在肯定句中可用before代替 Let's get in the wheat before the sun sets.）

否定句：
She didn't arrive until 6 o'clock.
她直到6点才到。
Don't get off the bus until it has stopped.
公共汽车停稳后再下车。
I didn't manage to do it until you had explained how. 直到你教我后，我才会做。

1)Until可用于句首，而till通常不用于句首。
Until you told me, I had heard nothing of what happened.
直到你告诉我以前，出了什么事我一点也不知道。
2)Until when 疑问句中，until要放在句首。
---Until when are you staying? 你呆到什么时候？
--- Until next Monday. 呆到下周一。

注意：否定句可用另外两种句式表示。
(1）Not until …在句首，主句用倒装。
Not until the early years of the 19th century did man know what heat is.
直到19 世纪初，人类才知道热能是什么。
Not until I began to work did I realize how much time I had wasted.
直到我开始工作，我才认识到了我已蹉跎了几多岁月。
(2) It is not until… that…
19.10 表示"一…就…"的结构

hardly/scarcely…when/before, no sooner…than 和as soon as都可以表示"一…就…"的意思，例：

I had hardly / scarcely got home when it began to rain.
I had no sooner got home than it began to rain.
As soon as I got home, it began to rain.

注意：如果hardly, scarcely 或no sooner置于句首，句子必须用倒装结构：
Hardly / Scarcely had I got home when it began to rain.
No sooner had I got home than it began to rain.

.If it doesn’t rain tomorrow, we will go hiking.
如果明天不下雨, 我们就去远足.
2.You will get good grades if you study hard.
如果你努力学习,就会取得好成绩.
3.I will go to the party unless he goes there too.
我会去参加聚会的, 除非他也去.(如果他不去,我就去.)
4.You will be late unless you leave immediately.
如果你不马上走,你将会迟到的.(=If you don’t leave immediately, you will be late.)
难点提示：用条件状语从句时要注意时态的正确使用,当主句是将来时的时候,从句要用一般现在时.
lHe will not leave if it isn’t fine tomorrow.
一般将来时， 一般现在时
lThey are going to have a picnic if it doesn’t rain next week.
一般将来时, 一般现在时

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