名詞性從句的語法功能相當于一個名詞詞組,一般分為主語從句、表語從句、賓語從句和同位語從句。
一、引導(dǎo)名詞性從句的連接詞
1.連接代詞:who, whose, whom, what, which。有詞義,在從句中擔任成分,如主語、表語、賓語或定語等。
2.連接副詞:when, where, why, how。有詞義,在從句中擔任成分,作狀語。
3.連接詞:that, whether, if, as if, that。無詞義,在從句中不擔任成分,有時可省略;if (whether), as if雖有詞義,但在從句中不擔任成分。
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連接代詞與連接副詞在句中不再是疑問詞,因而從句中謂語不用疑問式。連接代詞與連接副詞在從句充當句子成分,連接詞whether和if(是否),as if(好像)在從句中不充當句子成分,只起連接作用。根據(jù)句意,whether, if和as if都用不上時,才用that作連接詞(that本身無任何含義)。
二、主語從句
1.主語從句在復(fù)合句作主語。例:
Who will go is not important.
2.用it作形式主語,主語從句放在句末。例:
It doesn't matter so much whether you will come or not.
3.that引導(dǎo)主語從句時,不能省略。例:
That he suddenly fell ill last week made us surprised.
三、表語從句
1.表語從句在復(fù)合句中作表語,位于系動詞之后。例:
The question was who could go there.
2.引導(dǎo)表語從句的連接詞that有時可省去。例:
My idea is (that) we can get more comrades to help in the work.
四、賓語從句
1.賓語從句在復(fù)合句中作賓語。引導(dǎo)賓語從句的連詞that一般可省略。例:
I hope (that) everything is all right.
2.介詞之后的賓語從句,不可用which或if連接,要分別用what或whether。例:
I'm interested in whether you've finished the work.
I'm interested in what you've said.
3.whether與if都可以引導(dǎo)賓語從句,??苫Q。但下面幾種情況不能互換。
①賓語從句是否定句時,只用if,不用whether。例:
I wonder if it doesn't rain.
②用if會引起誤解,就要用whether。例:
Please let me know whether you want to go.(此句如果把whether改成if,容易當成條件句理解。)
③賓語從句中的whether與or not直接連用,就不能換成if;不直接連用,可換。例:
I don't know whether or not the report is true.
I don't know whether/if the report is true or not.
④介詞后的賓語從句要用whether引導(dǎo)。whether可與不定式連用。whether也可引導(dǎo)主語從句、表語從句、同位語從句、讓步狀語從句,以上均不能換成if。但引導(dǎo)條件從句時,只能用if,而不能用whether。例:
It depends on whether we have enough time.
Please come to see me if you have time.
五、同位語從句
同位語從句在句中作某一名詞的同位語,一般位于該名詞(如:news, fact, idea, suggestion, promise等)之后,說明該名詞的具體內(nèi)容。例:
I have no idea when he will be back.
The fact that he had not said anything surprised everybody.