非谓语动词与独立主格结构非谓语动词分为三类：不定式（infinitive）、动名词（gerund）和分词（participle）。
其特点是：1．不定式、动名词和分词可以做很多句子成分，但就是不能单独做谓语，这也是它们被称为"非谓语动词"的原因。
2．它们具有各种形态：一般式、主动态、被动态、进行态和完成态。
3．不定式和动名词可以做主语、宾语、表语、补语等。
但不管起什么作用，它们都具有动词的功能，但无语法上的动词性质，这一点可以通过它们不受主语的人称和数的限制体现出来。
4．分词起形容词和副词作用，可做表语、定语、状语，但不能做主语和宾语。
它也不受主语人称和数的限制。
一．不定式1.完成式不定式的一般形式所表示的动作, 通常与主要谓语表示的动作(状态)同时(或几乎同时)发生, 或是在它之后发生. 假如不定式所表示的动作, 在谓语所表示的动作(状态)之前发生, 就要用不定式的完成式.I am glad to have seen your mother (= I am glad I have seen your mother).(比较: I am glad to see you.)He is said to have written a new book about workers.He pretended not to have seen me.2.进行式如果主要谓语表示的动作(状态)发生时, 不定式表示的动作正在进行, 这时要用不定式的进行式.You are not supposed to be working. You haven’t quite recovered yet.We didn’t expect you to be waiting for us here.He pretended to be listening attentively.3.完成进行式在谓语所表示的时间之前一直进行的动作, 就要用不定式的完成进行式.The struggle was known to have been going for twenty years.We are happy to have been working with you.4.被动式当不定式的逻辑上的主语是不定式所表示的动作的承受者时, 不定式一般要用被动形式.It is an honor for me to be asked to speak here.She hated to be flattered.He wanted the letter to be typed at once.【例】Sir Denis, who is 78, has made it known that much of his collection ______ to the nation.A) has left B) is to leave C) leaves D) is to be left结合选项来看，全句的意思：“78岁的丹尼斯爵士已经向众人宣布他的许多收藏品将留给国家"。
收藏品是"被留给国家”，因此需要一个被动式做宾语，所以答案是D) is to be left。
（二）句法功能1.不定式作主语【例】It is not unusual for workers in that region _________.A) to be paid more than a month later B) to be paid later than more a monthC) to pay later than a month more D) to pay later more than a monthit 在句中作形式主语。
而不定式to be paid more than a month是句子的逻辑主语。
结合选项全句的意思是：“那个地方的工人一个多月后才得到工资是常有的事”，答案是A)。
2.不定式做宾语大部分动词可加不定式做宾语。
如：We are planning to build a reservoir here.【例】There is a man at the reception desk who seems very angry and I think he means _________ trouble.A) making B) to make C) to have made D) having made动词mean在本句中的意思是“打算”，后面只能接动词不定式做宾语。
所以答案是B) to make。
动词mean后面接名词和动名词时，意思是“表示……的意思、意味着”，所以选项A 和D错误。
3. 不定式做补足语补语用于补充说明主语或宾语。
（1）不定式做主语补足语【例】The ancient Egyptians are supposed _________ rockets to the moon.A) to send B) to be sending C) to have sent D) to have been sending在本句中，句首表示时间概念的ancient表明不定式动作在句子谓语动作之前，不定式要用完成式，因而答案是C)。
在本句中，该不定式完成式to have sent作主语补足语。
（2）不定式做宾语补足语这样的动词有：advice, allow, announce, ask, assist, authorize, bear, beg, bribe, cause, command, compel, condemn, deserve, direct, drive, enable, encourage, entitle, entreat, exhort, forbid, force, get, hate, help, implore, induce, inspire, instruct, intend, invite, lead, leave, like, mean, need, oblige, order, permit, persuade, pray, prefer, press, prompt, pronounce, recommend, remind, report, request, require, summon, teach, tell, tempt, urge, want, warn, wish。
这样的短语有：call on（请求）, care for（关心）, count on（依靠，指望）, depend on（依赖、依靠）, keep on at（困扰，追问）, long for（渴望）, make out（分辨）, vote for（选举）, prevail on（说服）, rely on（信赖）, wait for（等待）。
【例】They are going to have the serviceman __________ an electric fan in the office tomorrow.A) install B) to install C) to be installed D) installed全句的意思是：“他们准备让服务人员明天在办公室里装一台电扇”。
"have sb. do sth."句型的主动语态，因此，have 后接不带to的不定式作宾语补足语，所以答案是A) install。
4.不定式作表语One of our main tasks now is to mechanize agriculture.5.不定式做定语不定式做定语时，不定式修饰中心词或者不定式短语末的介词与中心词组成介词短语，修饰中心词（下面例1）。
这些动词不定式可能是及物的（带宾语），也可能是不及物的。
要特别注意如果不定式中的动词是不及物动词，则不定式后要加介词，因为此时不定式与其修饰的名词实质上有动宾关系。
很多名词后可接不定式做定语，如ability, ambition, anxiety, attempt, campaign, chance, courage, decision, determination, drive（动力）, effort, force, inclination, intention, method, motive, movement, need, opportunity, pressure, reason, right（权利）, struggle, tendency, wish, anything, anyone, everything, everyone, nothing, no one, something, some one等。
这类名词通常表示抽象概念，后面用动词不定式做定语，表示该名词的具体内容，解释前面中心名词（例2）在这种结构中，不能用分词形式。
【例1】Could you find someone________？A) for me to play tennis with B) for me to play tennis C) play tennis with D) playing tennis请你找个人来和我打网球。
答案是A。
【例2】The pressure ________causes Americans to be energetic, but it also puts them under a constant emotional strain.A) to compete C) to be competed B) competing D) having competed结合选项看，全句的意思是：“竞争的压力使美国人精力充沛，但也使他们的精神始终处于紧张状态。
”名词pressure后应加不定式做定语，说明"pressure"的内容。
6.不定式作状语不定式作状语可以表示目的、原因、结果等。
They stood by the roadside to talk about the plan．他们站在路边为的是谈论这个计划。
(目的)His family was too poor to support him．他的家庭太穷，不能维持他的生活。
(结果)We are glad to hear the news．我们很高兴听到这消息。
(原因) （三）动词不定式不带to的情形1. 在“动词+ 宾语+不定式”结构中, 如果动词是表示感觉意义的see, hear, watch, smell, feel, notice等, 或是表示“致使”意义的have, make, let等, 其后的不定式结构不带to.John made her tell him everything.这类结构转换为被动语态时, 后面的不带to 的不定式一般还原为带to 的不定式.She was made to tell him everything.2. 在had better, had best, would rather, would sooner, would just as soon, might (just) as well, cannot but 等搭配之后, 动词不定式也不带to.I’d rather not have eggs and bacon for breakfast.They cannot but accept his term.3. 在介词except, but 之后, 如果其前有动词do的某种形式, 不定式一般不带to, 反之带to.There is nothing to do except wait till it stops raining.Smith will do anything but work on a farm.There’s no choice but to wait till it stops raining.4. 连词rather than, sooner than 置于句首时, 其后的不定式不带to；出现在句中其他位置时, 其后的不定式有时带to, 有时不带to。