That是什么从句：That是引导从句的词，看到that从句先归入名词性从句和定语从句两大块；名词性从句里that作从属连词，把完整句子变成主语、宾语、表语或同位语；定语从句里that作关系代词，替代先行词并在从句里担任成分。
That的角色决定归类：当that只起连接作用，从句本身句子结构完整，它更偏名词性从句；当that替代前面的名词或代词，并在从句里承担主语或宾语成分，它更偏定语从句。
识别路径
- 看that后面能不能独立表达一个完整意思。
- 看that在从句里是否承担成分。
- 看that前面是否有名词、代词或先行词需要被修饰。
- 看that前面是否有动词、系动词、名词、句首位置需要接完整信息。
类型速查表
| 出现位置 | 从句类型 | That的角色 | 例句 |
|---|---|---|---|
| 动词后 | 宾语从句 | 从属连词 | I believe that the plan is good. |
| 句首 | 主语从句 | 从属连词 | That she arrived early made the teacher happy. |
| 系动词后 | 表语从句 | 从属连词 | The result is that the method works. |
| 名词后 | 同位语从句 | 从属连词 | The fact that English is useful motivates many learners. |
| 名词或代词后 | 定语从句 | 关系代词 | The book that is on the desk is interesting. |
| so后 | 目的或结果从句 | 连词 | He practices every day so that he speaks clearly. |
| in后 | 原因从句 | 连词 | I enjoy this lesson in that it is practical. |
使用清单
- 主语从句：That she won surprised everyone.
- 宾语从句：I hope that tomorrow is sunny.
- 表语从句：The key is that you understand it.
- 同位语从句：The idea that learning English is fun spread quickly.
- 定语从句：The phone that is on the table is new.
- 目的或结果从句：Study hard so that you master the grammar.
- 原因从句：This sentence works in that it gives clear information.
常见例句清单
| 例句 | That是什么从句 | That的作用 |
|---|---|---|
| I know that you are ready. | 宾语从句 | 从属连词 |
| That he is honest is obvious. | 主语从句 | 从属连词 |
| The truth is that the task is simple. | 表语从句 | 从属连词 |
| The fact that you came matters. | 同位语从句 | 从属连词 |
| The bag that I bought is nice. | 定语从句 | 关系代词 |
| The man that helped us is kind. | 定语从句 | 关系代词 |
| He opened the door so that we could enter. | 目的从句 | so that连接 |
| I like this plan in that it is clear. | 原因从句 | in that连接 |
【常见问题】
问题1 That是什么从句最常见的类别是什么
回答1 That是什么从句最常见的类别是名词性从句，that作从属连词，把完整句子放到主语、宾语、表语或同位语位置。
问题2 That是什么从句怎样快速识别
回答2 识别That是什么从句时，先看that的角色；如果that只连接信息，句子通常属于名词性从句；如果that替代前面的名词并担任成分，句子通常属于定语从句。
问题3 That是什么从句在写作里怎么用
回答3 在写作里使用That是什么从句时，可以先写一个完整信息句，再用that把它接到主句里；也可以用that连接先行词和修饰内容，让句子信息更集中。
问题4 That是什么从句和what从句怎么对比
回答4 对比That是什么从句和what从句时，看词义和成分；that主要起连接作用，what自带疑问词义，并在从句里承担主语或宾语等成分。
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