核心规则
不定式的基本形式是 to do，常带有未实现、目的、具体一次行为或对未来的指向。它可在句中作主语、宾语、表语、定语、补语和状语。
结构与例句
| 功能 | 例句 |
|---|---|
| 主语 | To communicate clearly is important. |
| 宾语 | We decided to wait. |
| 表语 | Our goal is to reduce waste. |
| 定语 | She has a report to finish. |
| 目的状语 | He left early to catch the train. |
| 宾补 | They asked us to stay. |
使用场景
不定式作主语较长时，常用 it 作形式主语：It is important to check the source。疑问词可与不定式构成 what/how/where to do。
常见错误
错误： I look forward to meet you. → 此处 to 是介词，应写 meeting。
错误： My parents made me to apologize. → 主动语态 make 后用省略 to 的不定式：made me apologize。
易混知识点
remember to do 表示记得去做，remember doing 表示记得做过。stop to do 表示停下原来的事去做另一件事，stop doing 表示停止该动作。
总结
先识别不定式的句法功能，再检查控制它的动词搭配，以及动作与谓语之间的时间和语态关系。
高中必修 · 不定式的基本功能
基本功能
不定式作目的状语时可用 in order to 或 so as to 强调；否定形式是 not to do。作后置定语时，它与所修饰名词可能是动宾、主谓或同位关系：a book to read；the first person to arrive；a plan to protect wildlife。
感官动词和使役动词后的宾补在主动句中可省略 to：I saw him cross the road；She made me wait。变为被动后，make 的 to 恢复：I was made to wait。
小练习
- 填空：She got up early ___ (avoid) the traffic.
- 改错：The teacher made us to rewrite the paragraph.
- 判断功能：He is the first student to finish the task.
参考答案
to avoid。- 删除
to。 - 不定式作后置定语，修饰 student。
选择性必修 · 不定式的完成式与被动式
进阶形式
to be doing 强调与谓语同时进行：He seems to be sleeping。to have done 表示动作早于谓语：She appears to have solved the problem。被动形式为 to be done，完成被动为 to have been done。
不定式有自己的逻辑主语时，常用 for + 名词/代词 + to do：It is necessary for us to prepare。描述人的品质时常用 of：It was kind of you to help。
小练习
- 填空：The bridge is expected ___ (complete) next year.
- 填空：He seems ___ (forget) our earlier conversation.
- 选择：It is difficult for / of beginners to master the pattern.
参考答案
to be completed。to have forgotten。for，difficult 描述任务对 beginners 的难度。