译林牛津版必修5Unit1同步讲解及练习（答案）学案（6）Grammar and usage ( To-infinitive )GrammarTo-infinitive.动词不定式由“不定式符号to+动词原形”构成，否定形式not to do。
是动词的一种非谓语的形式，在句中不能单独作谓语。
动词不定式具有动词的性质，可以有自己的宾语和状语，也可以有时态和语态的变化。
同时，它也具有非动词的性质，相当于一个名词、形容词或副词，可以在句中担任主语、宾语、宾语补足语、表语、定语和状语.动词不定式的用法：1、作主语(1)不定式短语在句中作主语。
谓语动词用单数形式。
e.g.: To say is one thing and to do is another.To know oneself is difficult.但在很多情况下，为了保持句子平衡，通常用it作为形式主语，而把不定式移到谓语之后，e.g.: It is difficult to know onself.It is important to learn English.2、作表语。
不定式作表语说明主语的具体内容或表示目的。
e.g.: His wish is to become an engineer.To live is to do something worthwhile.3、作宾语. 作动词的宾语，即动词+to do sth. 常见的要加不定式作宾语的动词有：decide/ determine, learn, want, expect/ hope/ wish, refuse, manage, pretend, offer, promise, choose, plan, agree, ask/ beg, afford, prefer, require, enable, need, order…e.g.: He agreed to meet here but so far she hasn’t turned up yet.He pretended not to see me when I passed by.在find, make, think, consider等动词后，如果宾语带有宾语补足语时，常用it作形式宾语，而把真正的宾语放在宾语补足语后.e.g.: I find it interesting to study English.I think it impossible to work out the problem.4、作宾语补足语，即Ｖ＋sb. (not) to do sth.如动词advise, allow, ask, cause, challenge, command, consider, enable, encourage, forbid, force, inform, invite, persuade, tell, send, urge, want,warn….Eg. I want you to speak to Tom.Ask him not to make noise.(1)在感官动词以及使役动词（let, have, make）后作宾语补足语，不定式都不带to.变为被动语态时，原不带to的不定式要变成带to的不定式.“一感(feel)二听(hear, listen to )三让(let, have, make )四观看(see, observe, watch, look at)”e.g.: I often hear him sing the song.Did you see him go out?The boss made the employees work ten hours a day.The employees were made to work ten hours a day.(2)在表示心理状态的动词后作宾语补足语,这时不定式通常是“to be+形容词或副词”的结构.这类动词有：consider, think, believe, find, imagine, judge, suppose, prove等。
