在功能上介乎主动词和助动词之间的一类结构，称为半助动词。下面是半助动词知识点，希望对考生有帮助。

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：

They are certain to win the game.他们肯定会在比赛中获胜。

→It is certain that they will win the game.

He is likely to let you down.他可能使你失望。

→It is likely that he will let you down.

He appears to have many friends.看来他有许多朋友。

→It appears that he has many friends.

He seems to be enjoying himself.看来他玩得很快活。

→It seems that he is enjoying himself.

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。例如：

He is adout to arrive.他即将到达。

He is bound to win!他一定会获胜!

The boy tended to be late.这孩子老是迟到。

不可以转换为：

*It is about that he will arrive.

*It bound that he will win.

*It tended that the boy was late.

半助动词也可用于there-存在句。例如：

There's going to be a storm.就要有暴风雨了。

There's to be an investigation.要作一次调查。

There has to be a mistake.一定有错。

There's sure to be some rain tonight.今晚一定有雨。

There's likely to be a large audience.观众人数可能很多。

There's certain to be trouble at the factory.厂里一定有麻烦。

There seems to be a widespread change of attitude

看来态度有普遍的改变。

There appears to be no doubt about it.

看来这是毫无疑问的了。

精品小编为大家提供的17年高考英语一轮复习半助动词知识点大家仔细阅读了吗?最后祝考生们学习进步。

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高考英语一轮复习助动词知识点  

2017高考英语动词考点：系动词知识点