【不定式有哪些】在英语语法中，不定式（Infinitive）是一个非常重要的结构，它由“to + 动词原形”构成。不定式在句子中可以充当多种成分，如名词、形容词、副词等。掌握不定式的用法和形式对于提高英语表达能力至关重要。
以下是常见的不定式类型及其用法的总结：
一、不定式的常见形式
| 形式 | 构成 | 说明 |
| 基本不定式 | to + 动词原形 | 如：to go, to eat, to write |
| 被动不定式 | to be + 过去分词 | 如：to be seen, to be done |
| 完成不定式 | to have + 过去分词 | 如：to have gone, to have eaten |
| 完成被动不定式 | to have been + 过去分词 | 如：to have been told, to have been invited |
二、不定式的功能与用法
1. 作主语
- To learn English is important.
- To see is to believe.
2. 作宾语
- I want to go.
- She asked to leave early.
3. 作表语
- My job is to teach.
- His dream is to travel the world.
4. 作定语
- I have a question to ask.
- There is nothing to worry about.
5. 作状语
- He studied hard to pass the exam.
- She left early to avoid the crowd.
6. 作补语
- I consider him to be honest.
- We elected her to be the leader.
7. 用于某些动词后
- afford to do, agree to do, decide to do, hope to do, need to do 等。
8. 用于某些形容词后
- happy to do, ready to do, eager to do 等。
三、特殊用法
- 疑问词 + 不定式
- I don't know what to do.
- She asked how to get there.
- without + doing / to do
- He left without saying goodbye.
- She went out without to say anything.
四、不定式的否定形式
- to not + 动词原形（现代英语中常用 to not）
- I decided not to go.
- She refused to help.
五、不定式的省略形式
在某些情况下，不定式中的 to 可以省略，尤其是在情态动词、助动词或感官动词之后。
- I saw him run.
- Let’s go.
- She made me do it.
总结
不定式是英语中一种多功能的语法结构，既可以表示动作本身，也可以表达目的、原因、条件等。掌握其基本形式和不同用法，有助于更准确地理解和运用英语语言。
| 类型 | 举例 | 用法 |
| 基本不定式 | to go | 作主语、宾语、表语等 |
| 被动不定式 | to be seen | 表示被动意义 |
| 完成不定式 | to have finished | 表示过去的动作 |
| 完成被动不定式 | to have been invited | 表示过去被动完成的动作 |
通过不断练习和积累，你将能更灵活地使用不定式，提升自己的英语表达能力。