職稱英語中名詞性從句是在句子中起名詞作用的主謂結構，它可以在主從複合句中作主語、賓語、表語、介詞的'賓語以及同位語。
主語從句主語從句可以由連詞that，wh-疑問詞或名詞性關係詞引導。
⑴由連詞that引導：從句可以位於句首，但常常用形式主語it替代，從句本身則放在主句後面，如：
That he will come to the party is certain. It happened that the harvest was bad that year. Is it true that she has never been there?
通常在口語或非正式文體中，that常可省略，但必須是在用先行詞it的情況下，如：
Its a pity you are leaving.
⑵由wh-疑問詞引導：從句既可以前置，又可以藉助於先行詞it後置。如：
Who cleaned the meeting room is unknown. Its still a question when we shall have our sports meet. It is uncertain whether he will come.注意：在疑問句中，wh-疑問詞所引導的從句不能位於句首，如：
Is it known where she went?
⑶主語從句也可由名詞性關係詞引導，這類從句只能位於句首，如：
Where she went was Los Angeles. What will be，will be. Whomever you invite will be welcome.