在句子中起名詞作用的從句叫名詞性從句(Noun Clauses)。名詞性從句的功能相當(dāng)于名詞詞組，它在復(fù)合句中能擔(dān)任主語(yǔ)、賓語(yǔ)、表語(yǔ)、同位語(yǔ)、介詞賓語(yǔ)等，因此根據(jù)它在句中不同的語(yǔ)法功能，名詞從句又可分別稱為主語(yǔ)從句、賓語(yǔ)從句、表語(yǔ)從句和同位語(yǔ)從句。
1. 主語(yǔ)從句
(1)三種連接詞
①?gòu)膶龠B詞：that，whether等。
that引導(dǎo)主語(yǔ)從句只起引導(dǎo)作用，本身無實(shí)際意義，在主語(yǔ)從句中不充當(dāng)任何成分，但不能省略。
That she left him cut him to the heart.
由whether及其他連詞引導(dǎo)的主語(yǔ)從句放在句首，句后都可。
Whether it will please them is not easy to say.
②連接代詞who，what，which，whatever，whichever，whoever。
What seems easy to some people seems difficult to others.
③連接副詞when，where，how，why等。
Why he did it remains a mystery.
(2)位置：主語(yǔ)從句可以前置，也可以后置。用it作形式主語(yǔ)，而把主語(yǔ)從句放在句末，常用下面幾種句型。
① It is still uncertain whether he is coming or not.
It + be + 表語(yǔ) + 主語(yǔ)從句表語(yǔ)：(名詞、形容詞、過去分詞)
② It seemed (happened, doesn’t matter, has turned out) that…
It doesn’t matter whether she will come or not.
It + 不及物動(dòng)詞 + 主語(yǔ)從句
③ It has been decided that the exhibition will not open on Sundays.
It is expected that the house price in Beijing will fall down.
It + 及物動(dòng)詞(被動(dòng)語(yǔ)態(tài))+ 主語(yǔ)從句
2.賓語(yǔ)從句
(1)由連接詞that引導(dǎo)的賓語(yǔ)從句
(2)主語(yǔ)+及物動(dòng)詞+連接代詞/連接副詞引導(dǎo)的賓語(yǔ)從句
None of us knows where these new parts can be bought.
賓語(yǔ)從句的語(yǔ)序是陳述句語(yǔ)序，即：連接代詞/副詞+主語(yǔ)+謂語(yǔ)+其他成分。
(3)主語(yǔ)+及物動(dòng)詞+whether/if引導(dǎo)的賓語(yǔ)從句，賓語(yǔ)從句要用陳述句語(yǔ)序，whether與if引導(dǎo)賓語(yǔ)從句時(shí)一般可以互換使用。
Please let us know whether (if) they will come to our party.
在discuss，wonder，not sure和介詞之后盡量用whether，if與whether含義容易混淆。
The board are discussing whether the fund should be allocated to that region.
(4)賓語(yǔ)從句中的否定轉(zhuǎn)移
若主句主語(yǔ)是第一人稱，謂語(yǔ)動(dòng)詞為think，consider，suppose，believe，expect，guess，imagine等，其后的賓語(yǔ)從句若含有否定意義，一般要把否定詞轉(zhuǎn)移到主句謂語(yǔ)上，從句謂語(yǔ)用肯定式。
I don’t think this dress fits you well. I don’t believe you will finish the work today.
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