动词不定式（二）3．作表语同时，不定式还可用作表语，表示主语的具体内容，也可以表示主语的目的、结果、同意、安排、命令、决定和劝告等意义，其主语可以是抽象名词、带to的不定式或以what 引导的名词性从句。
如果作表语的不定式含有疑问意义，可以根据要表达的具体意义在不定式前面加what, which, when, where, whether 和how等疑问词。
e.g. I) The most important thing is to put theory into practice.II) To do this would be to cut the foot to fit the shoe. 这样做是削足适履。
III) Our difficulty is where to find a guide.【注】如果主语分句或修饰主语的定语分句中部分中有all, what, 或形容词最高级等限制性比较强的词，并且使用了实义动词do 的限定或非限定形式，作表语的不定式中的to 可以省略。
e.g. I) The best we can do is remember our seven astronauts, our Challenger Seven.我们所能做到的最好方式是铭记住我们的7位宇航员，我们挑战者号的7位勇士。
II) All I did was (to) give him a little push.III) What they want to do is get the whole thing over so they can sit down and watchTV. 他们要做的是把不得不做的事一劳永逸地做完，然后可以坐下来看电视。
4. 作定语不定式作定语通常置于它所要修饰的词语之后，一般表示将要发生的动作，带有"将要"、"可能"、"应该"、"必须"和"需要"的意义。
有时不定式与它所修饰的词语之间含有逻辑上的主谓关系，有时不定式与它所修饰的词语之间含有逻辑上的动宾关系时，此时可以用主动形式的表示被动意义，如果这个不定式是不及物动词，它后面就应有必要的介词。
e.g. I) He was soon chosen as the man to speak for the party because he was a great orator.他是一个伟大的演说家，因而不久就被选为党的发言人。
II) She usually has a lot of meeting to attend.III) Whenever it is cold we have fuel to warm us and sheepskin coats to wear.天冷时，我们有燃料取暖，有羊皮衣御寒。
IV) Is this something to be ashamed of?不定式还常常用来修饰与动词或形容词有关联的名词，如wish, hope, need, decision, attempt (试图)，ability, necessity (需要)等等，注意这些名词相对应的动词或形容词后面也可以跟不定式。
e.g. I) The enemy failed in their attempt to land on the island.II) You should have confidence in your ability to fulfill (完成) the task.另外，“介词+ which + 不定式”结构也可以起定语作用。
e.g. I) She had no time left in which to pack her things. 她没有时间收拾行礼了。
II) He had a little money in the bank, with which to help his mother.他银行里有一点存款，用来帮助他的妈妈。
5. 作状语不定式作状语可表示原因、目的、结果、条件和行为方式。
a) 不定式作状语表示原因时通常用在表示情感和情绪的形容词后。
有此用法的形容词有：amazed (吃惊的) , angry, annoyed (苦恼的), anxious (焦虑的), ashamed (惭愧的，羞耻的), confused (困惑的), content (满足的), delighted (高兴的), disappointed,eager, fortunate (幸运的), frightened (害怕的), glad, happy, lucky, proud, sad, shocked(震惊的), slow, sorry, surprised, thankful, unable, unwilling (不情愿的), unwise,willing等。
e.g. I) He was annoyed to hear them talk like that.II) We shall be very happy to cooperate (合作) with you in the work.b) 作状语表示目的时，通常置于动词之后，但为了强调目的，也可将不定式位于句首。
此外，不定式也常在so as或in order后，不过in order (to) 可置于句首，而so as (to)则不行。
e.g. I) To do a good job, we must have the right tools.II) He wore strange clothes so as to show his contempt for the tradition. 他身着奇装异服以示对习俗的蔑视。
c) 表示结果的不定式通常位于句子的后半部，往往与表示程度的修饰语联用，最常见的表示结果的动词不定式结构有：such ＋（名词短语）as to ...，该结构中的名词或名词短语有时可以省略；so + 形容词（或副词）＋as to ...；形容词（或副词）＋enough to... ；too + 形容词(或副词) + to ...。
另外，动词不定式还可能表示一种意外的或令人不愉快的结果，如only to...结构。
e.g. I) What have I said to make you so excited?II) He made a long speech, only to show his ignorance of the subject.他讲了一大段话，只暴露出他对这么学问一无所知。
III) We found the room not big enough to hold so many people.IV) Your stupidity is such as to make me disappointed. 你傻得令我失望。
V) I’m just too busy to get a good night’s sleep.d) 而表示行为方式的不定式则通常由as if或as though引导。
e.g. They walked slowly, as if to prolong (延长) the wonderful evening.6. 作同位语作同位语的不定式常跟在名词或代词后面，有逗号、冒号或破折号与它所要说明的名词或代词分开。
e.g. The magazine went on to say that the menu really has two important functions: (1) tosell food; and (2) to repeat and emphasize the unique atmosphere of that restaurant.该杂志接着指出：菜单实际上具有两个重要功能：1）推销食品，2）重申并强调餐馆的独特氛围。
三、不定式中to的省略1. 在助动词或情态动词do (does, did), will, shall, would, should, can, may, must （除了ought, have, be）后面，应省略to。
e.g. I) They can find a solution.II) Some ancient Egyptians did not eat pork. 一些古埃及人不吃猪肉。
2. make, let, watch, see, hear, notice, feel, have, listen to后面跟不定式作其宾语补足语时，不定式中的to的应省略。
e.g. I) Father had my brother wash the car yesterday.II) She made me sit at the table.3. 在had better (最好), would rather (宁愿), cannot but (只能) 结构后面应省略不定式中的to; would rather...than...后面也常常跟不带to的不定式。
e.g. I) I think I had better take the earliest bus.II) I would rather have rice than have some noodles (面条)4. 两个或两个以上作用相同的不定式并列使用时, 第一个不定式前面有to, 而后面的不定式中的to 可省略。
e.g. It was his habit to go out at night and bring gifts to the poor.【注】如果两者之间有对比关系或不定式前有逗号，每个不定式前面都应有to。
e.g. It is usually easier to follow rules of social conduct than to depend on one’s own taste.遵循社会行为准则通常要比根据个人的情趣行事容易一些。
5. 在why或why not引导的问句中，如果没有主语，to应省略。
e.g. Why not try a second time?6. 当不定式用作主语补足语时，如果不定式所表示的意义是动词do意义的延伸，在all...do, what...do, the thing...do等句型中to可以省去。
e.g. The bus broke down. The only thing we could do was walk there.7. 作介词except 和but宾语的不定式，如果前面句中的动词是do或have的话，不定式不带to，否则不定式必须要有to。
