名词性从句¶
名词性从句在句子中起名词的作用，按充当的成分分为四种：
| 类型 | 在句中的作用 | 示例 |
|---|---|---|
| 主语从句 | 主语 | What he said is true. |
| 宾语从句 | 宾语 | I know that he is right. |
| 表语从句 | 表语 | The problem is that we have no money. |
| 同位语从句 | 解释前面的名词 | The news that he won surprised us. |
连接词¶
| 连接词 | 含义 | 在从句中的成分 | 示例 |
|---|---|---|---|
| that | 无意义 | 不充当成分 | I think that he is right. |
| whether / if | 是否 | 不充当成分 | I wonder whether he will come. |
| what、who、whom、whose、which | 什么、谁、谁的、哪个 | 主语、宾语、表语、定语 | I don't know what he wants. |
| when、where、why、how | 何时、哪里、为什么、如何 | 状语 | Tell me where you live. |
宾语从句中的 that 常常省略：I think (that) he is right.
陈述语序¶
名词性从句一律用 陈述语序（主语在前，谓语在后），即使连接词是疑问词也不例外。这是初学者最常犯的错误：
| ✓ | ✗ |
|---|---|
| I don't know where he lives. | I don't know where does he live. |
| Can you tell me what time it is? | Can you tell me what time is it? |
| I wonder if she is coming. | I wonder is she coming. |
宾语从句的时态¶
主句是一般过去时，宾语从句通常也要用相应的过去时态：
- He said (that) he was tired.（不说 is）
- She told me she would come.（不说 will）
从句表达的是客观真理时，仍用一般现在时：The teacher said that the earth goes around the sun.
主语从句与形式主语¶
主语从句较长时，常用 it 作 形式主语，把真正的主语从句放到句末：
- That he will come is certain. → It is certain that he will come.
- It doesn't matter whether you agree or not.
whether 与 if¶
两者都表示“是否”，宾语从句中通常可以互换。以下情况只能用 whether：
- 引导主语从句、表语从句、同位语从句：Whether he will come is unknown.
- 在介词后：It depends on whether it rains.
- 直接与 or not 连用：I don't know whether or not he will come.
- 后接不定式：I can't decide whether to go.
同位语从句与定语从句¶
两者都可以用 that 引导，放在名词后面，区别在于 that 在从句中是否充当成分：
| 类型 | that 的作用 | 示例 |
|---|---|---|
| 同位语从句 | 不充当成分，从句 解释 名词的内容 | The news that he won the match is true.（消息的内容是“他赢了比赛”） |
| 定语从句 | 充当成分（这里是宾语），从句 限定 名词 | The news that he told me is true.（他告诉我的那个消息） |
同位语从句常跟在 news、fact、idea、belief、hope、possibility 等抽象名词之后。