不定词，即to加上动词原型形成的短语。
不定词与助动词
- 不定词可视为助动词的变化形式，表达一种不确定性的语气
- 不定词与助动词二者共性
- 后面跟动词原形
例子：I will go./I want to go. - 有“不确定”的语气成分
例子：He may be right./He seems to be right. - 用完成时表示过去时间发生的事情
例子：It must have rained last night./It seems to have rained last night.
- 所有语气助动词都可以变换为不定词短语
- must ==> have to
- should ==> ought to
- can/could ==> be going to
- may/might ==> be likely to
动状词中的不定词
- 动状词
- 定义，由动词演变而来，具有动词样子，但不是动词
- 分类：动名词、不定词和分词（现在分词和过去分词）
- 词性：分词的词性为形容词，动名词为名词，不定词顾名思义，不确定词性，可以做名词、形容词或者副词
- 使用情况
- （谓语）动词后面一般跟名词（宾语），那么可以使用动名词或者不定词
- 不定词是意外，不确定，打算，将要的含义
- 动名词保留了动词的特点，同时兼具名词特征，即有动作的持续性已发生，正在做的含义
- 例子
- They plan to marry next month.
- I avoid making the same mistake twice.
- I hate to say this, but I think you're mistaken.
- I always try to be on time.
- Why don't you try being late for a change?
- The speaker stopped talking at the second bell.
- I remember calling her at 6:00 last night.
- Please remember to give me a wake-up call at 6:00 a.m. tomorrow.
使役动词/感官动词与不定词
- 使役动词
- 叫别人做事情，有命令强制的含义，后面接动词原形
- 常见使役动词，have/let/make/get/keep/help/leave等
- 例子：The teacher made the little girl stay behind.
- 感官动词（看/听/感觉）
- 感觉器官动词，只能配合确实发生的事情，所以跟动词原型/动名词（持续性）
- 常见感官动词，hear/see/watch/sound/look/feel/smell/taste
- 例子：I heard her cry out in pain.
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