在英语从句体系中，从属连词"that"作为宾语从句的引导词，虽无实际词义却在句子结构中扮演着不可或缺的角色——它既是语法功能的标志，也是语义连贯的桥梁。
从属连词that引导宾语从句时，具有以下三个典型特征：
| 语法特征 | 说明 |
|---|---|
| 无词义性 | 本身不表达具体含义，仅起连接作用 |
| 不作成分 | 在从句中不担任任何语法成分 |
| 可省略性 | 在非正式语体中常可省略（限制条件后文详述） |
最常见的使用场景，接在及物动词后构成动宾结构：
| 例句 | 语法分析 |
|---|---|
| I believe that he is honest. | that引导从句作believe的宾语 |
| She admitted that she had made a mistake. | that引导从句作admitted的宾语 |
| Research shows that regular exercise improves health. | that引导从句作shows的宾语 |
接在表达情感或认知的形容词后，形成"系表+宾语"结构：
| 例句 | 语法分析 |
|---|---|
| I am glad that you passed the exam. | that引导从句作形容词glad的宾语 |
| We are confident that our team will win. | that引导从句作形容词confident的宾语 |
| He was afraid that he would be late. | that引导从句作形容词afraid的宾语 |
通常情况下，介词后不直接接that从句，但少数介词例外：
| 例句 | 语法分析 |
|---|---|
| The plan depends on whether we get funding. （非that） | 介词后通常用whether而非that引导从句 |
| She complained about the fact that no one listened to her. | 通过"the fact that"结构间接接从句 |
| Except that it was too expensive, the car was perfect. | except that为固定搭配，允许接从句 |
that在宾语从句中的省略并非随意，需遵循特定语法规则：
| 可省略情况 | 必须保留情况 |
|---|---|
| 主句动词后直接接从句时 I think (that) he is right. |
从句位于句首时 That she is talented is obvious. |
| 非正式口语或书面语中 She said (that) she would come. |
多个宾语从句并列时 He said that he was tired and that he wanted to rest. |
| 从句主语为人称代词时 We know (that) they are coming. |
主句与从句之间有插入语时 Everyone believes, without doubt, that this is true. |
| that引导从句 | what引导从句 |
|---|---|
| I know that you need help. （我知道你需要帮助） |
I know what you need. （我知道你需要什么） |
| 仅起连接作用，无词义 | 兼具连接功能和从句成分 |
当宾语从句较长，而补语较短时，常用it作形式宾语：
| 常规语序 | 形式宾语结构 |
|---|---|
| I find that he always lies disappointing. | I find it disappointing that he always lies. |
| 从句直接作宾语，句式不平衡 | 用it作形式宾语，真实宾语后置 |
| 句子类型 | 正确示例 |
|---|---|
| 简单宾语从句 | Scientists have confirmed that the discovery is groundbreaking. |
| 并列宾语从句 | The teacher explained that the theory was complex but that it could be understood with effort. |
| 形容词+宾语从句 | We are certain that this investment will yield returns. |
| 错误示例 | 正确形式 | 错误分析 |
|---|---|---|
| I want to know that you need. | I want to know what you need. | that无词义，不能作need的宾语 |
| She insisted that she was right was obvious. | She insisted that it was obvious that she was right. | 从句嵌套混乱，需重整结构 |
深度解析：that引导宾语从句时，虽然在许多情况下可以省略，但学习者应当首先掌握完整结构，再学习省略规则。在正式写作中，保留that往往能使句子结构更清晰，避免歧义。
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