句之前，亦可放在主句之后），如：
As he didn't know much English, he got out his dictionary and looked up the word “cough”. 他对英语懂得不多，他拿出字典查找“cough”这个词。
As the ground is wet, it must have rained last night.（倒果为因） 昨晚一定下了雨，地面是湿的。
③ now that用来说明一种新情况，然后加以推论。now that放句首时that可省略： Now (that) everybody is here, let's begin.
3. for也可以表示原因，属并列连词，不是说明直接原因，而是对某种情况加以推断，表示补充说明理由。而推断的理由会因人而异。语气很弱，它引出的分句必须放在另一分句后。
He must be ill, for he is absent today.
4.原因状语从句有时可以用分词形式表现。 As he was blind, he couldn't see anything. Being blind, he couldn't see anything.
四、条件状语从句 1．由if, unless（if...not）, so/as long as, supposing(that)（假设）, in case（万一…, 以防…）, so/as far as（就...而言）, on condition that（条件是...）, provided/providing (that)（假若）引导。
Tell me about it if you have time. I won't go unless I'm invited.
Take an umbrella with you in case it rains.
You may use the room as/so long as you clean it up afterwards.
2.“祈使句+and/or/or else/otherwise+陈述句”的句型中，祈使句在意义上实际上相当于条件状语从句。
Use your head, and you'll find a way.
Hurry up or else (otherwise) you’ll be late.
3. if only也可以引导条件状语从句,只不过较少使用而已。only if也引导条件状语从句，意思是“只有在...条件下” If (only) it clears up, I will go.
4.条件状语从句中一般要用一般现在时态表将来。 I will go if you go.
5.条件状语从句中的省略问题
1)从句主语为it,又有系动词be时，可以省略从句中主语和be动词。 Come tomorrow if (it is) possible. If so, you must get back and get it.
还有诸如if necessary“如果有必要”，if any“如果有”，if in need“若需要”。
2）如果if从句的主语和主句的主语一致，谓语动词又有be,可以把从句中的主语和be省略掉。
If (water is) heated, water sends out steam. 6.条件句中的虚拟与倒装
① if引导的条件状语从句若与过去或现在事实不符，或对未来进行不可能的假设，就要
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用虚拟语气。（详见虚拟语气部分）
②省略if的虚拟条件从句：若条件从句的谓语动词有were, had或should,可以把if省去，而把were，had或should移到主语前构成倒装。 Had I arrived there earlier, I would have seen him.
Were it not for him, I would not have the chance to go home. Should he be here tomorrow, I would give him a hand.
五、目的状语从句 由so that（以便）， in order that（为了），for fear that（= in case）（以免），lest（以防）引导，谓语常含may, might, can, could, will, would等情态动词。 They set out early so that they might arrive at the station in good time. I'll speak slowly so that/in order that you can understand.
He wrote the name down for fear that（lest）he would forget.
★当从句与主句主语一致时，可用to do, so as to do, in order to do结构换用。 He worked day and night in order that he could succeed. He worked day and night in order to succeed.
六、结果状语从句
1.常用的连词有so that，so ... that, such...that, that（带古英语痕迹）。（结果状语从句中一般无情态动词）
He had overslept so that he was late for work. My pen fell under my desk that I couldn't see it. 2. so/such ...that所用句式 ①so + adj（adv) + that从句
The box is so heavy that I can't carry it.
②so+adj +a/an+单名+ that从句＝such a/an+adj.+单名+that从句 She is so beautiful a girl that all the boys of our class like her. =She is such a beautiful girl that all the boys of our class like her. ③so many/few +复名+ that从句
so much/little+不可数名词+ that从句
There are so many apples on the desk that we each have one. There is so little water that you can't drink. ④such +a/an + adj + 单名+ that从句
She is such a good girl that she can help you. ⑤such + adj +复名/不可数名+ that从句
It was such bad weather that we all stayed home.
He has such interesting books that he keeps reading all day. 注意 little表“小，可爱”时，用such不用so修饰。
He is such a little boy that his patents often teach him something.
七、方式状语从句
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由as, as if (as though)引导。 Do as you like.
He spoke as if he had been there before.
注意 as if, as though从句与事实相反时用虚拟语气，与事实相符，不用虚拟语气。
八、比较状语从句
①常用连词than, as ...as..., not as/so... as He ran as far as he could. I'm not as/so tall as he/him.
She studies harder than I（study）．
②the more ... the more...引导, 且经常以省略形式出现 The harder you try, the better you will understand.
九、让步状语从句
由though, although, as, even if/though , no matter wh-, wh-ever词，whether...or（不管...都），when, while等引导。
1. though, although这两个连词用法基本一样，只是前者口语化，后者较正式，常位于句首，都不与but连用，但可以和yet，still，nevertheless连用。though还可作副词单独放在句尾，表示“然而”的意思。
Although the TV set is very dear, I still want to buy it. Though /Although he was worn out, he kept on working. 2. as引导让步状语时，从句部分用倒装语序，句型为: ①形容词/副词/名词+ as +主 +谓 ②动词+ as +主 +情态动词 Child as he is, he knows a lot.
Proud as these nobles are, they are afraid to see me. Great a scientist as he is, he remains modest. Try as I might, I couldn't lift the stone.
注意 在这种倒装结构中，也可以用though（不太常用），但不可用although.
Bravely though the players fought, they had no chance of winning. 3. even if（尽管；即使）, even though（尽管）
这两个复合连词意义基本相同，常用以强调让步概念，有退一步想的意思（有时用于虚拟）。表“即使”时有假设含义，一般用even if。 We'll make trip even if(though) the weather is bad.
Even if I were in your place, I wouldn't take the job.（虚拟） 4.“whether... or...”可引导让步状语从句 Whether you believe it or not, it is true. 5.“no matter + wh-”引导让步状语从句
引导让步状语从句时“疑问句-ever”相当于“no matter +疑问词”，此时： no matter who = whoever
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no matter what = whatever no matter which = whichever no matter where = wherever no matter how = however
No matter what happened, he would not mind.
It's a nice room no matter whom (whoever) it belongs to.
6.“no matter + wh-”结构只能引导让步状语从句，而“wh-ever”形式除引导让步状语从句外，还可以引导名词性从句。 引导名词性从句时：
whoever = anyone who任何…的人…
whatever = anything that任何…的事（物） whenever = anyplace where任何…的地方 I will give the book to whoever needs it. I like whatever you like.
7.when引导让步状语从句时置于主句后 ①虽然···却···，尽管···但···
He walks when he might take a taxi. ②本（应...，可以...）却...。
when从句用虚拟式为：could/should ... have done She stopped trying when she might succeed next time.
8.while引导让步状语从句时置于主句前，与though同，但though从句可到装，while从句不可倒装。
9.让步状语从句中用一般现在时表将来。 No matter what he is, he will be punished.
十、状语从句的省略现象
当状语从句的主语与主句的主语相同或为it, 同时从句谓语含be动词，就可省去从句的主语和be动词。 ①时间状语从句中：
Don’t speak until (you are) spoken to. While (I was) in Beijing, I lived with my uncle. I want to go swimming when (it is) possible. ②条件状语从句中：
Come tomorrow if (it is) possible. If (it is) so, you would be punished. Unless (it is) repaired, the TV set is of no use. ③方式状语从句中：
She stood at the gate as if (she was) waiting for someone. ④其他状语从句中：
Though (it was) cold, he still wore a shirt. Fill in the blanks with proper words where (it is) necessary.
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