动词不定式用法动词不定式没有人称和数的变化，在句中不能独立作谓语。
但动词不定式具有名词、形容词和副词特征，在句中可以作主语、宾语、宾语补足语、定语、表语和状语等多种成分。
另外，动词不定式具有动词特点，可以有自己的宾语和状语，组成动词不定式短语。
动词不定式的肯定形式是to＋do；其否定形式是not to＋do。
下面以动词不定式在句中的作用来予以详细说明。
1．作主语可以直接作主语。
如：To see is to believe．但在英语中，常用it作形式主语，真正的主语即动词不定式放在后面。
如：It's wrong to play tricks on other people．It's our duty to keep our environment clean and tidy．点击规律：动词不定式在句中作主语时，常放在It is ＋adj +(for sb.)＋(not)to do sth句型中，表示说话人对客观事件的决断，意为：做…..是……的，it仅作形式主语，真正的主语是to do sthIt is very interesting to read.读书是有趣的It is useful to read.看书是有用的It is healthy to run every day.每天跑步是健康的It is a little difficulty for me to work out this question.解出这道题对我来说有点难It is bad not to finish homework.不完成作业是糟糕的It is bad to be late for school.迟到是糟糕的It is+adj+of sb +(not)to do sth该句型通常表示说话人对客观事件的惊讶、兴奋、懊悔、难过等感叹情绪，与It is ＋adj +(for sb.)＋(not)to do sth的意义不同。
It is very kind of you to tell me the truth．你能告诉我事实，真是太好了It is stupid of him to do such a silly thing．他做那件傻事，真是太笨了It is very clever of you to work out this question. 你能解出这道题目，真是太聪明了It is very wise of you to read this novel. 你看这本小说，真是太明智了这个句型中用介词of而不是for的原因是这里的形容词是用来形容人的品质性格的。
类似的词有：careless，careful，clever，considerate，foolish，good，impolite，kind，naughty，nice，silly，stupid，friendly因此区分是用It is ＋adj +(for sb.)＋(not)to do sth还是It is+adj+of sb +(not)to do sth，要清楚adj修饰的是sb还是to do sth例如：It is nice for me to have breakfast with you（nice是指have breakfast with you这件事）对于我来说，能和你一起吃早餐真好。
It is nice of you to help him with his English.（nice是指you，形容人的品质）你帮他补习英语，真是太好了。
2．作宾语a．want，decide ，agree，afford，agree，aim，appear，ask，believe，care，claim，decide ，demand，desire，determine，expect，fail，happen，hesitate，hope，intend （有打算），learn，long（渴望），manage，offer，pretend，promise，prepare，refuse，seek，swear（发誓），undertake（承担），want，wish等动词后面跟并且只能跟不定式。
如：We agreed to start early．She wants to be a doctor．b．love，like ，begin，start，hate ，prefer等词后面可以接不定式。
点击规律：上述动词后面除接不定式外，还可以接动名词，意思无很大区别。
提示板：like doing指经常性动作，而like to do指一次性的动作。
如：I like swimming，but I don't like to swim now．我喜欢游泳，但我现在不想游。
c．stop，forget，remember，go on ，try等词或短语后面可以接不定式。
点击规律：上述动词后面接不定式和接动名词意思大不相同。
提示板：1）stop to do sth．：停止一件事，去做另一件事。
stop doing sth．：停止正在做的事。
2）forget to do sth：忘记要去做某事（未做）forget doing sth：忘记做过某事（已做）3）remember to do sth：记得去做某事（未做）remember doing sth：记得做过某事（已做）4）go on to do sth：接着做另一件事（接下去做与原来不同的一件事）go on doing sth：继续不停的做某事或间断后继续做原来没有做完的事5）try to do sth：试着做某事（实际上意思是努力想做成某事eg:I tried to escape,but I failed.我努力着想逃走，但是没有成功）Try doing sth：试着做某事（实际上是为了达到另外一个目的，-------"So hot here,isn't it?" -------"Yes,why not try turning on the air conditioner?" "很热，是吧。
" “恩，就是。
咱们开开空调吧，看看能不能凉快点儿。
”）例句：When the teacher came in，the students stopped talking；when he came out，the students stopped to talk．当老师走进来时，学生们停止说话；当老师走出去时，学生们又开始说话。
d．在find／feel＋it＋adj．＋to do sth．句型中，it是形式宾语，真正的宾语是后面的动词不定式。
就是说不定式由it代替，把不定式放到后面去。
这可以用这一结构表达：动词(如find，think，consider，feel等)+it+ 形容词+不定式。
如：She considers it necessary to make friends with him.We find it difficult to finish all the homework before 9 o’clock.The man downstairs found it difficult to get to sleep．I feel it easy to recite the text．e. 动词+疑问代(副)词+不定式：这类动词常见的有advise，decide，find out，forget，inquire，know，learn，see，regard，remember，teach，tell，understand，wonder等。
常见的疑问代(副)词有: what，when，where，which，how，whether等。
1.He does not know when to start.2.You can decide whether to continue or to stop.3.I will show you how to deal with it.3．作宾语补足语a．tell，ask，want，order，teach，invite，warn，wish，help，get，wish，help等词后面常接不定式作宾补。
如：I tell him not to go there by bus ．Edison's mother taught him to read and write．b．let，make，have，see，hear，feel，watch，notice后面接不带to的不定式作宾补。
如：The boss makes them work 16 hours a day．I heard her sing in the next room．提示板：若变成被动语态，在上述结构中，不定式符号to要加上。
如：They are made to work 16 hours a day by the boss．She was heard to sing in the next room．4．作定语：放在被修饰的名词、代词后面例句：I have a lot of work to do．He could do nothing to help the boy．There was really nothing to fear．He gave me an interesting book to read点击规律：动词不定式若在句中作定语，常放在被修饰的名词、代词之后。
提示板：如果动词不定式和前面所修饰的词构成动宾关系，若动词是不及物动词，切记不要忘掉介词。
如：I have a small bedroom to live in．Have you got some pens to write with？Mary needs a friend to play with．That girl has nothing to worry about．They have a strict teacher to listen to．5．表语：放在连系动词be后面例句：His wish is to become a scientist．The first important thing is to save the soldiers' lives．当务之急是抢救战士们的生命。
点击规律：动词不定式在句中作表语时，通常对连系动词前面的名词进行诠释说明。
6．作状语a．目的状语：放在go，come，use，live，in order等词后面。