原因结果目的状语从句

原因、结果和目的状语从句
一、原因状语从句
引导原因状语从句的连词有：because，since，as，seeing (that)，now (that)等。

because表示直接的原因或理由，着重点在从句，用于回答why提出的问句，语气最强，常译为“因为”。

例如：
He is absent today because he is ill.
—Why were you late for class this morning?
—Because I missed the early bus.
since一般表示对方已知的、无须加以说明的既成事实的理由，相当于as it is the fact that…。

全句中心在主句，语气比because弱，常译为“既然”。

例如：
Since you are busy, I’ll go alone.
as表示十分明显的原因，一般说明因果关系，着重点在主句，语气较弱，常译成“由于”。

例如：
As it is snowing, we shall not go to the park.
注意：as和since的差别不大，它们通常位于主句之前，有时也可位于主句之后。

as表示的原因语气最弱，常用于口语。

seeing that和now that也常用于引导原因状语从句，相当于since，意为“既然”。

例如：Seeing that the weather is bad, we’ll stay at home.
另外，for也可表示原因，但其引导的是并列分句，而非从句，for前往往须用逗号或分号隔开，for不能表示直接原因，只是提供解释或补充说明的作用，且不可位于句首。

例如：
I didn’t go to see him, for a heavy snow was falling.
The days were short, for it was now December.
二、结果状语从句
结果状语从句用于so (that)，so…that，such…that结构。

结果状语从句一般位于主句之后。

例如：
He made a wrong decision, so that half of his lifetime was wasted.
The box is so heavy that nobody can move it.
It is such a difficult problem that nobody can work it out.
so用于修饰形容词或副词，such用于修饰名词。

具体来说，有以下七个句型：
1. so ＋adj. ＋that从句
This story is so interesting that I want to read it again.
2. so ＋adv. ＋that从句
He spoke so quickly that I couldn’t follow him.
3. so ＋adj. ＋a/an ＋可数名词单数＋that从句
It was so fine a day yesterday that we all went out for a picnic.
4. so＋many/ much / few / little＋名词＋that从句。

I’ve had so many falls that I’m black and blue all over.
There was so little water in the jar that it was not enough for all of us.
5. such ＋a/ an ＋(adj.) ＋可数名词单数＋that从句
She made such a good meal that we all ate far too much.
6. such ＋(adj.) ＋可数名词复数＋that从句
We visited such wonderful cities that we didn’t want to leave.
7. such ＋(adj.) ＋不可数名词＋that从句
They had such trouble that they once intended to give up.
有三点需要特别说明一下：
1. 句型3和句型5可以互换，例如：
He has such an important meeting to attend that he can’t come to your party.
= He has so important a meeting to attend that he can’t come to your party.
2. little表示数量时，用so，而不是such。

例如：
There is so little food in the house that I have to go and buy some.
但若little不是表示数量，而表示“小”时，则应使用such。

例如：
They are such little birds that we should feed them with our food.
little前到底用so还是such，除根据其意义来区分外，还可看其所修饰的名词是可数还是不可数名词，若为可数，使用such，若为不可数，则使用so。

3.“so (such)…that”结构中的so或such部分提前置于句首时，主句应使用倒装结构。

例如：
So many questions did they ask me that I myself got confused.
Such a terrible noise did she hear that she was scared to death.
三、目的状语从句
引导目的状语从句的还有：so that，in order that。

例如：
They started early so that they might arrive in time.
He works hard in order that he can win the first place.
注意：so that既可引导目的状语从句，又可引导结果状语从句，其区别在于：1. 引导结果状语从句时通常用逗号同主句分开；2. 引导目的状语从句时，从句中要使用情态动词，而引导结果状语从句时，不使用情态动词；3. 引导目的状语从句时，可位于句首。

试比较如下：
I got up late, so that I missed the bus. (结果)
I got up early so that I could catch the bus. (目的)
The teacher spoke loud, so that all the students heard him clearly. (结果)
The teacher spoke loud so that all the students could hear him clearly. (目的)
So that all the students could hear him clearly, the teacher spoke loud. (目的)。