不定式用法专讲
8 有关不定式短语结构的几个问题
在使用不定式短语时，如果有必要，我们可以用以 引起的短语来表示它逻辑上的主语。带有这种短语的不定式结构，可以用来：
1)作主语：
It is now rare for anyone to be absent without leave. 擅自缺席的情况现在很少了。
How would it be for me to look after the machine? 我来看这台机器怎么样?
2)作宾语：
I don't think it advisable for him to study medicine. 我看他学医不合适。
Do you consider it worthwhile for them to make that experiment?
你认为他们做这试验值得吗?
3)作定语：
We'd better find some work for the children to do. 最好找点工作给孩子们做。
There are a lot of difficulties for them to overcome. 多困难需要他们克服。
4)作状语：
I stepped aside for her to pass. 我站到一边让她过去。
The text is too long for us to learn by heart.
课文太长，我们记不住。
They arranged for her to do light work in the factory.
安排她在厂里干轻活。
5)作表语：
The best thing would be for us to build the skating-rink with our own hands．
最好是我们自己动手修溜冰场。
This is for you to decide. 这得由你决定。
Another solution was for them to take charge of it jointly. 另一个办法是让他们共同负责。
不定式短语，在某些情况下，前面可以带一个连接代(副)词。这种不定式结构接近一个名词从句，常用在某些动词(如：tell, show, know, decide, teach, learn, discuss, wonder, remember, find out, explain, forget)等后面作宾语：
He will advise you whether to do it. 是否要这样做他会给你出主意的。
We'd better find out where to put it.
我们最好了解一下应放在哪里。
Have you decided when to hold the party?
你们决定没有什么时候举办这个晚会?
She will tell you which bus to take. 她会告诉你坐哪路公共汽车。
Do you know how to express the idea in English?
你知不知道这意思英文怎样表达?
也可用在某些介词后作宾语：
They exchanged views on the question of whom to elect.
他们就选举谁的问题交换了意见。
They were at a loss as to how to meet the situation.
他们惊惶失措，不知如何应付这一局面。
I was thinking of how to fulfil our task.
我在考虑如何完成我们的任务。
They did research on how to raise the forage yield.
进行研究如何提高饲料产量。
有时介词可能省略掉：
We enquired (about) where to go. 我们询问该到哪里去。
I was careful (over) what to say. 我很注意该说些什么。
有时也可以作主语(a)，表语(b)，状语(c)或同位语(d)：
a. It is not yet decided whether to build the dam here.
是否在这里修水坝还没决定。
How to divide labour among ourselves will be discussed at the meeting.
如何分工将在会上讨论。
b. The question is how to put the plan into practice.
问题是如何把这计划讨诸实施。
c. She was at a loss (as to) what to do. 她不知如何是好。
I had no idea which one to take. 我不知道拿哪个好。
d. The question whether to confess troubled the girl.
是否要坦白的问题使姑娘很烦恼。
不过用这种结构作主语、表话或状语的时候不及用从句的时候多。在没有把握的时候，最好不要用这种结构，用从句反而容易一些。上面句子中的这种结构都 可以用从句代替：
It is not decided whether we should build the dam here． 没决定是不是把大坝修在这儿。
The question is how we are to put the plan into practice. 她不知道怎样办
注：在口语中我们有时会听到Where to go now? What to do next? 这样的句子，但有些语法家觉得这样说不太好。但Why do it this way? Why not do it today? 这类句子已被公认是正确英语了。
to是不定式常常带有的一个小品词(particle)，但在下面情况下，它总是被省略掉的：
1)在一般的助动词或情态动词(如do，will，shall，would, should，can，may，must等)后面：
"May I come in?""Yes, please." "能进来吗?""请进。"
但在ought, have和be后不能省略。
2)在带有复合宾语的某些动词(如make，let，watch，see，hear，notice，feel，have，listen to等)后面：
I'll have my daughter mend the shirt for you. 我来让我女儿给你补衬衫。
在help后面的不定式可以要to，也可以不要。
3)在why引起的下面这类问句中：
why spend such a lot of money? 为什么要花这么多钱?
Why bother? 费这心干吗?
Why worry about such trifles? 干吗为这些小事发愁?
Why not wait for a couple of days? 干吗不等一两天?
Why not do it right now? 何不现在就干?
why not let her have a try? 何不让她试试?