1）由從屬連詞that引導的從句叫做名詞性that-從句。 that只起連線主句和從句的作用，在從句中不擔任任何成分，本身也沒有詞義。名詞性that-從句在句中能充當主 語、賓語、表語、同位語和形容詞賓語，例如：
主語：that he is still alive is sheer luck. 他還活著全靠運氣。
賓語：john said that he was leaving for london on wednesday. 約翰說他星期三要到倫敦去。
表語：the fact is that he has not been seen recently. 事實是近來誰也沒有見過他。
同位語：the fact that he has not been seen recently disturbs everyone in his office.
近來誰也沒有見過他，這一事實令辦公室所有的人不安。
形容詞賓語：i am glad that you are satisfied with your job.
你對工作滿意我感到很高興。
2）that-從句作主語通常用it作先行詞，而將that-從句置於句末，例如：
it is quite clear that the whole project is doomed to failure. 很清楚，整個計畫注定要失敗。
it's a pity that you should have to leave. 你非走不可真是件憾事。
用it作形式主語的that-從句有以下四種不同的搭配關係：
a. it + be +形容詞+ that-從句
it is necessary that… 有必要……
it is important that… 重要的是……
it is obvious that… 很明顯……
b. it + be + -ed 分詞+ that-從句
it is believed that… 人們相信……
it is known to all that… 從所周知……
it has been decided that… 已決定……
c. it + be +名詞+ that-從句
it is common knowledge that… ……是常識
it is a surprise that… 令人驚奇的是……
it is a fact that… 事實是……
d. it +不及物動詞+ that-分句
it appears that…似乎……
it happens that…碰巧……
it occurred to me that… 我突然想起……