本篇文章仅是个人理解，可能不是很正确，还需后续修正补充。

1 半助动词概念

半助动词在功能上介于主动词和助动词之间的一类结构，称为半助动词。

• (1) 半助动词充当情态动词。协助主动词。后接动词原型。
• (2) 半助动词充当主动词。具有时态和语态，每一个半助动词只能表示一种时态，一种语态。后接省略to的动词不定式或名词。

2 半助动词有哪些？

半助动词分四类：

• (1) be 型
• (2) have 型
• (3) seem 型
• (4) 特殊的

2.1 be 型

一般be + 形容词/介词 + to

be + 形容词 + to

eg:

• be able to
  • (1) 作情态动词
    • An open-minded person is able to adapt to new conditions.
      一个开明的人能够适应新情况。
  • (2) 作主动词
    • He should be able to lead a perfectly normal life.
      他应该能够过上完全正常的生活。
• be going to
  • (1) 作情态动词
    • He is going to recite a poem.
      他将要朗诵一首诗。
  • (2) 作主动词
    • I’ll be going to London for a few days.
      我要去伦敦去待几天。
• be likely to
  • (1) 作情态动词
    • He is likely to let you down．
      他可能使你失望。
  • (2) 作主动词
    • We’ll be likely to hire several people this month.
      这个月我们很有可能雇佣一些人
• be meant to
  • (1) 作情态动词
    • Beaujolais is meant to be a really good wine.
      博若莱葡萄酒是公认的佳酿。
  • (2) 作主动词
    • You must be meant to play the piano.
      你一定注定就是要弹钢琴。
• be obliged to
  • (1) 作情态动词
    • Every clause is obliged to obtain a finite verb.
      每个句子必须包括一个限定动词。
  • (2) 作主动词
    • I shall be obliged to go tomorrow.
      明天我不得不去。
• be supposed to
  • (1) 作情态动词
    • The price is supposed to be marked on the shelf
      价格应该标在货架上。
  • (2) 作主动词
    • Our country should be supposed to take this law as the main basis to response to the thunderbolt.
      我国应对突发事件就应该以该法为主要依据。
• be willing to
  • (1) 作情态动词
    • He is willing to wait.
      他情愿等待。
  • (2) 作主动词
    • Few firms will be willing to gamble on new products .
      很少有公司愿意冒险开发新产品。

be + 介词 + to

• be about to
  • (1) 作情态动词
    • We were about to start when it rained.
      下雨时，我们即将出发。
  • (2) 作主动词
    • new era seemed to be about to dawn for the coach and his young team
      对于那名教练和他的年轻球队来说，一个崭新的时代似乎即将到来。
• be due to
  • (1) 作情态动词
    • President Bush is due to visit the country next month.
      布什总统定于下月访问该国
  • (2) 作主动词
    • The results could simply be due to chance.
      这结果可能纯属意外。

2.2 have 型

eg:

• have to
  • (1) 作为情态动词
    • The boy has to make a living by begging.
      男孩不得不通过乞讨维持生计。
  • (2) 作主动词
    • You’ll have to move ─ you’re in my way.
      你得挪一挪，你挡了我的路。
• have got to
  • (1) 作为情态动词
    • They have got to abide by the rules.
      他们必须遵守规则。
  • (2) 作主动词
    • They will have got to Shanghai by this time tomorrow.
      明天这个时候他们就已经到上海了
• had better
  • (1) 作为情态动词
    • I had better give a few particulars about myself.
      我最好还是详细讲一下我自己的情况。
  • (2) 作主动词
    • pass

2.3 seem 型

eg:

• seem to
  • (1) 作情态动词
    • He seems to be very disappointed.
      他好像非常失望。
  • (2) 作主动词
    • Nobody here can seem to find you.
      似乎没有人找得到你
• appear to
  • (1) 作情态动词
    • The Democrats now appear to be in the lead.
      现在看来好像民主党人占优势。
  • (2) 作主动词
    • Time would appear to be the significant factor in this whole drama.
      时间似乎是整部剧中一个举足轻重的因素。
• come to
  • (1) 作情态动词
    • We come to the crux of the matter.
      现在我们来谈问题的症结。
  • (2) 作主动词
    • his hard work should come to nothing.
      他的所有辛勤劳动竟全部付诸东流。
• fail to
  • (1) 作情态动词
    • I fail to see the logic behind his argument.
      我不明白支持他论据的是什么逻辑
  • (2) 作主动词
    • The song can’t fail to be a hit.
      这首歌不可能不流行起来。
• get to
  • (1) 作情态动词
    • pass
  • (2) 作主动词
    • We have to get to the root of the problem.
      我们必须找到问题的根源。
• happen to
  • (1) 作情态动词
    • I happen to have the official statistics with me.
      我身边恰好有官方的统计数字。
  • (2) 作主动词
    • That would happen to us if we left the country.
      如果我们出国时，也会这样。
• tend to
  • (1) 作情态动词
    • People tend to work hard at this stage of life.
      人在这个人生阶段往往发奋努力
  • (2) 作主动词
    • I can’t tend to them both alone.
      我一个人照料不了两家。
• turn out to
  • (1) 作情态动词
    • pass
  • (2) 作主动词
    • Even the best theory can turn out to be wrong.
      即使是最好的理论最终也可能是错的。

2.4 补充

半助动词在用法上是介于主动词和助动词之间的一类词，表达情态意义，后接动词原形，却可以加助动词。一般末尾带to 的是半助动词，但并不是所有带to的都是半助动词，如look forward to,want to等词就不是半助动词。

3 半助动词特殊用法

3.1 be + adj + to 的半助动词的特殊用法

3.1.1 It…that-分句

带有半助动词作为动词词组的组成部分的句子，有的可以转换为“ It…that-分句”结构，而有的却不可以。从这个角度看，半助动词可分为两类：一类是可以作上述转换的，其中包括be cer-tain to，be（un）likely to，appear to，happen to，seem to等。例如：

讯享网

I happen to have had some nasty experiences in dealing with him．
我恰巧有过一些和他打交道的不愉快的经历。
→It happens that I have had some nasty experiences in deal－ing with him．

Some members of the committee seem to have been bribed．
委员会的一些成员看来是受了贿赂。
→It seems that some members of the committee have been bribed．

另一类半助动词不可以作上述转换，这一类包括be about to，be bound to，be going to，be to，had better，have to，have got to，tend to 等。

3.1.2 there

3.3 口语中半助动词的省略式

在结束本节以前，还要提一下半助动词的省略式问题。在口语中，had better，have got to和be going to有时可用省略式。例如：

You（'d） better go now．你最好现在就去。

You（'ve）just got to help me．你得帮帮我呀。