原因狀語從句
原因狀語從句，指在句中用來說明主句原因的從句。引導原因狀語從句的從屬連詞有because(因為), as(由於), since(既然), now(that)(既然), when(既然), seeing (that) (由於，鑑於), considering (that)(考慮到), for(為), given (that) (考慮到)等。
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目錄
原因狀語從句的類型及用法
一、引導原因狀語從句的從屬連詞 [1]
主要的有because,for,in that,for the reason that;as,seeing (that), seeing as;since;now (that); considering (that)等:
The woolly shrank because it was washed badly.
毛衣因為洗滌的方法不好而縮水。[2]
I can't get to sleep because of the noise outside.
由於外面聲音嘈雜我睡不着。
Since(As) we've no money, we can't buy it.
由於我們沒錢，我們不能購買它。
Seeing that it's raining, we'd better stay indoors.
既然外邊在下雨，我們最好待在室內。
Now that you are here, you'd better stay.
你既然來了，最好還是留下吧(既來之，則安之)。
【注】除以上提到的大家比較熟悉的引導原因狀語從句的從屬連詞外，when有時也可引導原因狀語從句(when表示"既然")
I won't tell you when you won't listen.
既然你不想聽，那我就不告訴你了。
二、關於not…because結構
該結構中的否定詞有時否定主句，有時否定從句，一般要根據句子的意思作出正確或合乎邏輯的理解。若not否定主句，最好在because之前用逗號，否則會引起歧義，如下句在沒有特定上下文時就有兩種解釋:
I didn't go because I was afraid.
我沒有去是因為怕。/ 我不是因為怕才去的。
不過若because之前有just修飾，一般認為not 是否定從句的:
You shouldn't get angry just because some people speak ill of you.
你不要因為有人說你壞話而生氣。
三、because不能與so連用
漢語習慣上說"因為…所以…"，但英語習慣上卻不能將 so與because 連用:
因為下雨，所以我們得呆在家裡。
正:Because it was raining, we stayed at home. / It was raining, so we stayed at home.
誤:Because it was raining, so we stayed at home.
四、because從句與 because of短語的轉換
Because引導的原因狀語從句有時可與because of 短語轉換，because of後加的原因可以為好或壞
但最正規的還是because
He can't come because he is ill. / He can't come because of his illness.
他因病不能來。
I said nothing about it because his wife was there. / I said nothing about it because of his wife's being there.
因為他妻子在那兒，我對此事隻字未提。
比較:because, since,as和for的區別:
1) because引導的原因狀語從句一般放於主句的後面，because從句位於句首時要用逗號分開，放在句末時，可不用逗號分開。because表示直接原因， 語氣最強， 最適合回答why引導的疑問句。because of 也表示原因，但它後面不接從句, 只能接名詞, 代詞或動名詞。注意:because 和so 不可同時出現在一個句子裡。
I do it because I like it. = I like it so I do it. We went by bus because it was cheaper. = It was cheaper so we went by bus. He can't go to school because of his illness. 2) since引導的原因狀語從句一般放於主句之前表示已知的、 顯然的理由(通常被翻譯成"既然"= now that )， 較為正式， 語氣比because弱。
Since you are free today, you had better help me with my mathematics. Since you don't trust him, you should not employ him. Now (that) you are grown up, you should not rely on your parents. 3) as 引導原因狀語從句時表示附帶說明的"雙方已知的原因"，含有對比說明的意味，語氣比since弱， 較為正式， 位置較為靈活(常放於主句之前)。
As it is raining, you'd better take a taxi. As you are tired, you had better rest. I went to bed early, as I was exhausted. 4) for引導的是並列句表示原因但並不說明主句行為發生的直接原因， 只提供一些輔助性的補充說明， for引導的並列句只能放於主句之後並且必須用逗號將其與主句隔開。
He could not have seen me, for I was not there. He seldom goes out now, for he is very old.
用法
原因狀語從句表原因， 以下逐一介紹中考、高考中常見的原因狀語從句的引導詞:
1. because引導的原因狀語從句一般放於主句的後面，because從句位於句首時要用逗號分開，放在句末 時，可不用逗號分開。because表示直接原因， 語氣最強， 最適合回答why引導的疑問句。
例如:
I do it because I like it.
我做這件事是因為我喜歡。
You can trust those products because the quality never varies.
你可以信賴那些產品，因為它們的質量從來不變。
We went by bus because it was cheaper.
我們乘公交汽車去，因為這樣便宜一些。
注意: "not ... because"結構中的not否定的是because引導的整個從句，
例如:
誤:The country is not strong because it is large. 正:The country is strong not just because it is large. 國強不在大。
I didn't help him,not because I was unwilling,but because I was unable to do it.
我沒有幫助他，不是因為我不願意，而是因為我力不從心。
2. since引導的原因狀語從句一般放於主句之前表示已知的、 顯然的理由(通常被翻譯成"既然")， 較為正式， 語氣比because弱。
例如:
Since you are free today, you had better help me with my mathematics.
既然今天你休息， 你最好幫我補習數學。
Since you don't trust him,you should not employ him.
你既然不信任他，你就不該雇用他。
注意: seeing (that)， now (that)， considering (that)， in that這幾個詞彙與since引導的原因狀語從句意思相近， 都表示"既然"。
例如:
Seeing (that) he refused to help us, there's no reason that we should now help him.
他既然曾經拒絕幫助我們， 我們沒有理由要來幫助他。
Now (that) you are grown up, you should not rely on your parents.
既然你長大了， 就不應該依靠你的父母了。
Considering (that) everybody is here, let's begin our discussion.
既然大家都到了， 我們就開始討論吧。
In that he is ill, he feels unable to do it.
因為他生病了，他覺得做不了那件事。
3. as 引導原因狀語從句時表示附帶說明的"雙方已知的原因"， 語氣比since弱， 較為正式， 位置較為靈活(常放於主句之前)。
例如:
As it is raining, you'd better take a taxi.
既然在下雨， 你最好乘出租汽車。
As you are tired, you had better rest.
既然累了， 你最好休息一下。
I went to bed early, as I was exhausted.
我睡得早， 因為我已筋疲力盡了。
4. for引導的是並列句表示原因但並不說明主句行為發生的直接原因， 只提供一些輔助性的補充說明， for引導的並列句只能放於主句之後並且必須用逗號將其與主句隔開。
例如:
He could not have seen me, for I was not there.
他不可能見過我， 因為我不在那裡。
He seldom goes out now,for he is very old.
他難得出門了，因為他年事已高。
注意:
①in view of the fact that可用as/since/seeing that來表示，但不能用because:
As/Since/Seeing that you are gere，you may as well give me a hand.
既然你在這裡，你就幫我個忙吧。
As/Since/Seeing that Tom knows French,he'd better do the talking.
既然湯姆懂法語，最好讓他來談。
②在as/since/seeing that意指以前共知的或共知的陳述時，可用if來代替:
As/Since/Seeing/If you don't like Bill。why did you invite him?
既然/如果你不喜歡比爾，你為什麼邀請了他?
考題解析
____ you've got a chance, you might as well make full use of it. (1999)A. Now that B. After C. Although D. As soon as[答案] A[解析] 主句與從句之間存在因果關係， 且"you've got a chance"表示一個顯而易見的原因， 因此應選用表原因的now that。
He found it increasingly difficult to read, ____ his eyesight was beginning to fail. (2006北京)A. and B. for C. but D. or[答案] B[解析] "his eyesight was beginning to fail"是"he found it increasingly difficult to read"的原因， 因此本題應選用可以表示原因的連詞for引導原因狀語從句。
A man cannot smile like a child, ____ a child smiles with his eyes, while a man smiles with his lips alone. (2006湖南)A. so B. but C. and D. for[答案] D[解析] 下劃線處之後的句子補充說明"a man cannot smile like a child"的原因， 應選用for表原因。