英语的从句（subordinate clause）按语法功能分为 三大类：
类别 功能 举例 在主句中充当
名词性从句（Noun Clause） 像名词一样 I know that he is right. 主语 / 宾语 / 表语 / 同位语
定语从句（Relative Clause） 修饰名词 The man who is talking is my teacher. 修饰名词或代词
状语从句（Adverbial Clause） 修饰动词/形容词/副词/整个句子 I will go when it stops raining. 作时间、原因、条件、目的、结果、让步、比较、方式等状语
🧩 一、名词性从句（Noun Clause）
名词性从句 = 连接词 + 主语 + 谓语
可由 that, whether, if, what, who, whom, whose, which, where, when, why, how 等引导。
类型 举例 功能
主语从句 That he failed is surprising. 作主语
宾语从句 I think (that) he is right. 作宾语（that 可省略）
表语从句 The truth is (that) he lied. 作表语
同位语从句 The news that he passed the exam is true. 解释名词（the news, the idea, the fact 等）
📌 that 可省略的条件：
仅在宾语从句中，且该从句紧跟动词时，如：
✅ I think (that) he’s right.
❌ The fact (that) he’s right is clear.（不能省略）
🧱 二、定语从句（Relative Clause）
定语从句用来修饰名词或代词，由关系代词或关系副词引导。
1️⃣ 关系代词引导（who / whom / whose / which / that）
代词 先行词 在从句中作什么 举例
who 人 主语 The man who came here is my father.
whom 人 宾语 The girl whom you met is my friend.
whose 人/物 定语（表示所属） The boy whose bike was stolen cried.
which 物 主/宾语 The book which you bought is interesting.
that 人/物 主/宾语 The person that helped me is kind.
2️⃣ 关系副词引导（when / where / why）
副词 对应名词 举例
when time The day when we met was rainy.
where place The house where I live is old.
why reason The reason why I came is simple.
📌 省略情况：
关系代词作宾语时可省略：
The book (which / that) I read was great.
作主语时不能省：
The man who helped me was kind.
⚡ 三、状语从句（Adverbial Clause）
状语从句修饰动词、形容词、副词或整个句子。常见的类型如下👇
类型 连接词 举例
时间 when, while, before, after, since, until, as soon as I’ll call you when I arrive.
原因 because, since, as I stayed home because it rained.
条件 if, unless, as long as, provided that You’ll pass if you work hard.
目的 so that, in order that I study so that I can pass.
结果 so...that, such...that He ran so fast that he fell.
让步 although, though, even if, while Although it’s late, I’ll go.
比较 than, as...as He is taller than I am.
方式 as, as if, as though He talks as if he knew everything.
地点 where Sit where you like.
🧠 四、从句省略与合并
有时从句可以简化为非谓语形式或短语：
完整从句 简化形式
When he arrived, we started. On arriving, we started.
Although he was tired, he worked. Tired, he worked.
The man who is standing there is my dad. The man standing there is my dad.