不定式的全称是“动词不定式”，是一种非限定动词，由不定式符号 to+动词原形构成。不定式具有动词的特征，同时也有名词、形容词和副词的特征。动词不定式是一种非限定性动词，由 to+动词原形构成，但它还是属于动词，所以它本身可以带宾语和状语。动词不定式在句中可以作主语、宾语、表语、定语和状语，还可用在复合结构中，而且有完成式、进行式、完成进行式和否定形式。

一）不定式的常考形式：

1)一般形式： He decided to work harder in order to catch up with the others.

被动形式: He preferred to be assigned some heavier work to do.

语法功能：表示与谓语动词同步发生

2)完成形式： He pretended not to have seen me.

被动形式： The book is said to have been translated into many languages.

语法功能：表示发生在谓语动词之前

二）不定式常考的考点：

1）不定式做定语 - - - -将要发生

2）不定式做状语 - - - -目的

3）不定式充当名词功能 - - - To see is to believe.

三)不定式的省略

1)感官动词 see, watch, observe, notice, look at, hear, listen to, smell, taste, feel

+ do表示动作的完整性，真实性；

+ doing表示动作的连续性，进行性

I saw him work in the garden yesterday.

昨天我看见他在花园里干活了。(强调"我看见了"这个事实)

I saw him working in the garden yesterday.

昨天我见他正在花园里干活。（强调"我见他正干活"这个动作）

"感官动词后面接形容词而不是副词： The cake tastes good; It feels comfortable.

2)使役动词 have bid make let等词后不定式要省略但同 1)一样被动以后要还原 to

I&# 39; d like to have John do it.

I have my package weighed.

Paul doesn&# 39; t have to be made to learn.

3) help help sb do help sb to do help do help to do

四)有些动词后只跟不定式如：

want， wish， hope， manage， promise， refuse， pretend， plan， offer， decide， agree， expect allow sb to do, cause sb to do, permit sb to do, enable sb to do

force sb to do. be more likely to do love to do warn sb to do be able to do

be ambitious to do. begin to do. start to do

五)有的时候 to后面要接 - ing形式

accustom (oneself) to; be accustomed to; face up to; in addition to; look forward to; object to; be reduced to; resign oneself to; be resigned to; resort to; sink to; be used to; be alternative to; be close/ closeness to; be dedication/ dedicated to; be opposition/ opposed to; be similarity/ similar to.