第一, 子句之前一定要有that、whether或疑問詞 (who、when等); 第二, 子句不能做句子使用, 換言之, 子句不能獨立存在。
例: That he works hard. (╳, 此為子句)
He works hard. (○, 此為句子)
Who he is? (╳, 此為子句)
Who is he? (○, 此為特殊疑問句)
Whether he will come? (╳, 此為子句)
Will he come? (○, 此為一般疑問句)
名詞子句與名詞一樣, 在句中可用作主詞、及物動詞的受詞、或置於be動詞之後作主詞補語。
a. 主詞
例: That he is a good student is true.
(他是好學生, 這是事實。)
Whether he'll come is not known yet.
(他是否會來尚不得而知。)
How he'll do it is still a mystery.
(他將如何做這件事仍是個謎。)
注意:
名詞子句作主詞時, 往往會形成主詞過大的毛病, 故一般皆用代名詞it代替這些子句, 形成下列句子結構:
It is true that he is a good student.
It is not known yet whether he'll come.
It is still a mystery how he'll do it.
b. 受詞:
例: I believe that he can do it.
及物動詞
(我相信他能做這件事。)
I don't know whether he'll come.
及物動詞
(我不知道他是否會來。)
He asked me where I live.
及物動詞
(他問我住在何處。)
注意:
1) that引導的名詞子句作及物動詞的受詞時, that可予省略。
例: I believe that he can do it.
= I believe he can do it.
(我相信他能做這件事。)
2) whether引導的名詞子句作及物動詞的受詞時, whether可被if取代, if仍譯成『是否』而非『如果』。
例: I don't know whether he'll come.
= I don't know if he'll come.
(我不知道他是否會來。)
c. 主詞補語
例: The truth is that he has no money.
(事實的真相是他沒錢。)
The question is whether he'll come.
(問題是他是否會來。)
The trouble is when we can finish it.
(問題是我們什麼時候才能做完這件事。)
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