词谓语动非在句中充当除谓语以外的句子成分的动词形式叫做非谓语动词。
非谓语动词分为三种形式：不定式、动名词和分词（分词包括现在分词和过去分词）.不定式一、不定式的作用1、作主语不定式作主语时，谓语用单数。
往往用it 作形式主语，把不定式放在谓语后面。
如：It took us two hours to finish the job.It is impossible for us to get there on time.It is very kind of you to help us.注意：（1）其他系动词如look, appear等也可用于此句型。
（2）当不定式作主语的句子中又有一个不定式作表语时，不能用Itis …to…的句型。
试比较：It is to negate my own idea to believe him.（错）To believe him is to negate my own idea .（对）（3）It is+ adj. of / for sb. to do sth. 结构中，当不定式的逻辑主语和前面的形容词可以构成系表结构时，用of, 否则用for.2、作宾语（1）动词+不定式。
如：He managed to escape from the fire.I find it hard to get along with him.（it 作形式宾语）注：下列动词通常用不定式作宾语：want, try, hope, wish, need, forget,know, promise, refuse, help, decide, begin, start, learn, agree, choose, get等不定式”相当于名词，作宾语。
如：+“特殊疑问句+to , 疑问词+动词）2（．t know what to do next/ how to do it next. I don't decide when to go there.I can'注意：不定式短语作宾语时，如果还带有宾语补足语，往往把不定式短语放在宾语补足语之后，用it 作形式宾语。
如：I find it necessary to learn a foreignlanguage.、作宾语补足语3 不定式（to do ）。
如：）动词+宾语+（1He warned me to be careful.I want you to speak to Tom.（不带to的不定式）What makes you think soask, tell, order ,want ,get, would 注：可以用动词不定式做宾补的动词有：like, like, advise, invite, allow, help, wish,warn, expect, prefer, encourage+ to be 的不定式结构。
如：表见解、看法的动词结构可为：动词+宾语（2）We consider Tom to be one of the best students in our class.The book is believed to be useful.（被动语态）There +不定式。
如：(3)我们没料到会有那么't expect there to be so many people there.We didn 多人在那里。
regard, think, believe, 短语作补语，像as 注意：（1）有些动词需用。
如：take, consider 我们认为汤姆是我们最好的老师。
We regard Tom as our best teacher. Mary took him as her father. 玛丽把他当作自己的父亲。
have, let, makehear, listen to（二听），2）在动词feel （一感），（即：吾看三室两（五看）(（三让），notice, see, watch, observe, look at，但变为被动语态后，必等后面的补足语中，不定式不带to厅一感觉) to。
如：须带The boy was seen to fall off the They saw the boy fall off the tree.tree.(3)help后面作宾语补足语的不定式可以带to, 也可以不带to.I often help him （to）clean the room.I helped him (to) find his things.4、作定语不定式作定语，修饰名词或代词，不定式和它所修饰的名词之间有逻辑上的主谓关系、动状关系、同位关系或动宾关系。
不定式通常要放在这些被修饰的词后。
如：I have a lot of work to do.（动宾关系）He is looking for a room to live in.（动状关系）He is the first person to think of the idea.（主谓关系）He has got a chance to go abroad.（同位关系）注意：1.不定式的逻辑主语是句子的主语时，不定式用主动形式表被动。
如：Do you have anything else to say2.如果作定语的不定式是一个短语，则要保留不定时短语中的副词或介词。
如：我需要一直钢I need a pen to write with . (I will wirte with the pen ) ()笔写字我有I have a little baby to look after .(I must look after the little baby ) ()一个婴儿要照看作状语，表示目的、结果、原因等，有时还有一些固定搭配的不定式短语，如to等。
…as to, ….enough to, too…in order to , so as to, so…as to, such .as, in order to, so as to, so(such)…做目的状语，to, only to （仅仅为了））（1 …（如此···以便···）如：to He ran so fast as to catch the first bus. 他飞快地跑以便赶上第一班车。
He came to the school to see his son.作结果状语，表事先没有预料到的，要放在句子后面。
如：（2）He hurried to the post office only to find it was closed.He searched the room only to find nothing.做原因状语。
如：（3）We were very excited to hear the news.m glad to see you.'I 做条件状语。
如：4）（To turn to the left , you could find a post office.作表语5、动词后面，构成表语。
如：be不定式可放在The question is how to put it into practice.My question is when to leave.His dream is to be a doctor.Her work is to look after the babies.不定式在句中作表语时，对应的谓语动词用单数。
注意：1. 2. 当助于是不定式时，表语不能用Ving形式，可用不定式。
如：To see is to believe. （眼见为实）6、独立结构。
如：To tell you the truth, I don't agree with you.To make matters worse, it began to rain.二、不定式的时态和语态1、不定式的时态（1）现在时：有时与谓语动词表示的动作同时发生，有时发生在谓语动词的动作之后。
如：He seems to know this. I hope to see you again.（2）完成时：表示的动作发生在谓语动词表示的动作之前。
如：I'm sorry to have given you so much trouble.He seems to have caught a cold.（3）进行时：表示动作正在进行，与谓语动词表示的动作同时发生。
如：He seems to be eating something.（4）完成进行时：表示动作从过去某个时间开始，一直延续到现在，并有可能持续下去。
如：She is known to have been working on the problem for many years.不定式的语态、2．当不定式的逻辑主语是其动作的承受者时，就用被动式。
如：He asked to be sent to work in Tibet. He was seen to enter the hall.to 的动词不定式三、省）外，情态动词（除ought ought to1、Would rather, had better.2、等后作see, watch, look at, notice, observe, hear, listen to, smell, feel 感官动词3、to.宾补，省略不能省略掉。
如：注意：在被动语态中toThe boss made them work He was seen to dance. I saw him dance.the whole night.They were made to work the whole night.let, have, make.、使役动词4He 可以省去。
如：连接的两个不定式，第二个to and, or 和than5、由wants to move to France and marry the girl.to, help sb. (to) do sth. 也可不带可带to ,6、Help……/Why not7、Why的动词不定to 时，后面出现的动词用不带except 前是动词do 8、But 和He wants to do nothing but go out. 式。
试比较：He wants to believe anything but to take the medicine.to be . discover, imagine, suppose, think, understand 等词后，可以省去9、通常在如：他应该是个好人。