join的四种用法
动词不定式
巧记动词不定式的用法
不定式有标记，to与动原连一起。没有人称数变化，动词特点它具备。
主宾定状表补语，唯独作谓不可以。not加上不定式，否定结构要牢记。
疑问词与不定式，构成短语有意义。仔细推敲多思考，准确判断有依据。
具体用法
一、动词不定式的基本形式是“不定式符号to+动词原形”，有时可以不带to。动词不定式没有人称和数的变化。在句中不能单独作谓语，但仍保留动词的特性，可以有自己的宾语、状语等。
动词不定式同它的宾语和状语一起构成不定式短语。
例如：to sell flowers in the street  在街上卖花 to speak in the classroom  在教室里讲话
不定式省to有四种情况：
1、使役动词let, make, have等后接不定式。
例如：Let him go!  The boss made the child labors work the whole night.
2、would rather, had better后。例如：You had better stay at home.
3、Why…/Why not…后。例如：Why not have a good rest on Sunday?
4、感官动词see, watch, look at, hear, listen to, smell, feel, find，notice 等后作宾语补足语，省to。
例如：I saw him dance.
注意：这些情况在被动语态中，不可省to.  例如：The child labors were made to work the w
hole night.
二、动词不定式具有名词、形容词和副词的特征，可以作句子的主语、表语、宾语、宾语补足语、定语和状语。
1、用作主语
直接把动词不定式置于句首的情况不多，多数情况用it作形式主语，把真正的主语——动词不定式置于句末，特别是不定式短语较长时。动词不定式作主语，谓语动词用第三人称单数形式。带疑问词的不定式短语作主语常置于句首。
例如：The head teacher said it was necessary to talk with his mother.
    How to make requests politely is important.
2、用作表语
动词不定式作表语，常用在be动词及seem, appear, happen等词之后，构成系表结构。说明主语的内容、性质、特征。
例如：The best way to improve your English is to join an English club.  She seem to be well-known.
3、用作宾语
○1. 用作宾语的动词不定式，常用在动词ask, choose, agree，expect, hope, decide, learn，prefer, know，wish, want, would like / love等及物动词之后，构成动宾短语。
例如：We decided to talk to some students about why they go there.
    He prefers to eat white bread and rice.    I’d love to visit Mexico.
○2.动词feel, find, make, think, believe等，在语法上不能接受不定式作宾语，只有用it作形式宾语，从而把动词不定式后置。句子结构是：主语＋feel / find / make / ... it+adj. / n.+。
例如：I find it difficult to remember everything.
○3.既可接动词不定式又可接v-ing形式作宾语，意思差别不大的动词有begin, start, like, love
等。一般说来，动词不定式表一次、数次的具体动作的全过程，v-ing形式表习惯性的连续动作。但这种区别并不很严格，特别是美式英语，即使是习惯性的动作也可以用动词不定式。
例如：Then I started to watch English-language TV.
    I’m beginning to understand my Chinese roots, and who I am.
（begin用了进行时态，后面只接不定式作宾语，表示事情刚开始，还要继续下去。）
○4.后接动词不定式或v-ing形式作宾语，意思差别较大的动词有forget, remember等。后接不定式作宾语，表动作尚未发生；后接v-ing形式作宾语，表动作已经发生。stop to do停下来做另外一件事，to do是目的状语；stop doing停止做、不做当前这件事，doing是宾语。try to do尽力做，try doing试试看；go on to do接着做另外的事，go on doing继续做原来的事。
例如：When I left home, I had forgotten to bring it with me.
    I stopped using them last year.
○5后只接v-ing作宾语的一些常用特殊动词：give up, enjoy, practice, finish, mind等。
例如：    Would you mind opening the window?　
4、用作定语
用作定语的动词不定式一般都位于被修饰的名词之后。
例如：I have so much homework to do today.    I cant think of any good advice to give her.
  通常chance, place, time, way等名词后接不定式作定语。另外在the first, the second, the last, the only等词后，也常用不定式作定语。
例如：He needs time to do homework.    You want to know the best way to get around the city.
5、用作补语
○1.常见动词不定式作宾语补足语的动词主要有：要求允许提议警告（ask, allow, permit, advise，warn），期望邀请鼓励（expect, suppose, invite, encourage），教导告诉想要（teach, tell, want），希望愿意（ wish, would like / love）。
例如：I invited her to have dinner at my house.  Teenagers should be allowed to choose their own clothes.
○2.动词不定式作补语，在主动语态句里不带to，被动语态句里带to时多数动词是感官动词和使役动词，包括四“看”：look at, observe, see, watch，三“让”：have, let, make，二“听”：hear, listen to，一“感觉”：feel，一“注意”：notice。
例如：This picture makes me feel tense！  Of course we want to see Liu Yu achieve his dreams.
○3.help后接动词不定式作补语，to可带可不带。一般说来，带to表间接帮助，不带to表直接帮助。在被动语态句里，或者用不定式的否定式作补语时要带to。
例如： They can help you to compare two different products so that you can buy the one you really need.
  Using e-mail English helps you write quickly.
○4.be said, be sure, happen, seem等后面可以接带to的动词不定式作主语的补语。
例如：He doesn’t seem to have many friends.    Be sure not to miss them if they come to a city near you.