在複合句主句中名詞性成分之後與該名詞性成分並列，補充說明該名詞性成分的有關情況的名詞性從句， 被稱為同位語從句。

同位語從句例句-that引導

例句：He referred to Copernicus’ statement that the earth moves round the sun

解析：在某些名詞(如suggestion, resolution等)後面的同位語從句要用虛擬語氣。引導同位語從句的連詞that通常不省略，但在非正式文體中也可以省去。that引導同位語從句與引導定語從句的區別：that引導同位語從句時只起連線作用，不充當任何成分;that引導定語從句時，在從句中要作成分，如主語、賓語等。

同位語從句例句-由whether引導

例句：We are not investigating the question whether he is trustworthy

解析：whether 可引導同位語從句，但if不能引導同位語從句。

同位語從句例句-連線代詞引導

例句：Have you any idea what time it starts？

解讀：在no idea, question, problem等後可用wh-疑問詞引導同位語從句，if不引導同位語從句。

同位語從句例句-連線副詞引導

例句：I have no idea when he will come back.

同位語從句的先行詞

通常為answer, hope, fact, truth, belief, news, idea, promise, information, conclusion, order, suggestion, problem, question, thought, report, belief, decision, doubt, opinion, theory等抽象名詞。

同位語從句的引導詞

通常有連詞that，whether，連線代詞和連線副詞等。

引導名詞性從句時what與whatever, who與whoever的區別：

what 與whatever：

What you want has been sent here.(what = the thing(s) that/all that/anything that特指)

Whatever you want makes no difference to me.(whatever = anything that泛指)

who 與whoever：

Who will go to Beijing on business has not been decided.(who表疑問，表示“誰”，“哪一個”)

Whoever breaks the law should be punished.(whoever = anyone who，表示“無論哪個人

suggestion作“建議”解，後面跟同位語從句時，以及suggestion用作主語，後面跟表語從句時，從句中的謂語動詞均用虛擬語氣。

如：

My suggestion is that the work (should) be started at once.我的建議是馬上開始工作。

The monitor’s suggestion that she (should) come another day has not been accepted.班長提出的她改天來的建議還是沒有被接受。

在suggestion，advice，request，order，demand，requirement等意為“建議，要求，命令”的名詞後，同位語從句中的謂語動詞通常用“should+動詞原形”的虛擬語氣結構，句中的should可以省略。

例句：I followed his advice thatI (should) finish my homework before supper time.我聽從了他要我晚飯前做完作業的建議。

The suggestioncame from the chairman that the new rule (should) be adopted.採納新規則的建議是主席提出來的。

The manager gave the order thatall the work (should) be completed in two weeks.經理下令所有的工作都必須在兩個星期內完成。