A 不定式结构用在acknowledge，assume，believe，claim，consider，estimate，feel，find，know，presume，report，say，think，under- stand等动词之后。（参见第245节。）

People consider／know／think等that he is这种句子有两种被动形式：

It is considered／known／thought etc．that he is

He is considered／known／thought etc．to be

同样：

People said that he was jealous1 of her．

大家说他妒忌她。等于：

It was said that he was

He was said to be jealous of her．

据了解他妒忌她。

在这两种结构中，用不定式的后一结构比较简洁。它主要用于be，尽管有时其他动词的不定式也可以如此用：

He is thought to have information which will be useful to the police．

大家觉得他学会了对警察有用的状况。

如句中所想到的内容涉及到以前的动作，则用不定式的完成式，因此：

People believed that he was等于：

It was believed that he was／He was believed to have been

People know that he was等于：

It is known that he was／He is known to have been

这种结构可与任何动词的不定式的完成式连用。

B 不定式结构用在suppose后

1 suppose的被动态之后可以接任何动词的不定式的一般式，但这种结构一般都含有这是一种责任、义务的意思，因此并非同suppose的主动态（常意为推断）完全对应的形式：

You are supposed to know how to drive．

你本该会开车。等于：

It is your duty to know／You should know how to drive．

会开车是你的责任。／你该了解如何开车。

但He is supposed to be in Paris既可能意思是他应该在那里，也会是指大家猜想他在那里。

2 suppose的被动态后面同样可以跟任何动词的不定式的完成式。这种结构可以有责任和义务的意思，但也常常没这种含义：

You are supposed to have finished．等于：

You should have finished．

你早就应该完成了。

但：

He is supposed to have escaped disguised2 as a woman．等于：

People suppose that he escaped

据猜测他是乔装打扮成女性逃跑的。

C 用在被动态动词后面的不定式一般是带to的不定式，尽管主动态动词后面可能带的是不带to的不定式：

主动态： We saw them go out．

大家看见他们出去了。

被动态： They were seen to go out．

有人看见他们出去了。

主动态： He made us work．

他强迫大家干活。

被动态： We were made to work．

大家被迫干活。

然而，惟独let的被动态后面的不定式不带to：

主动态： They let us go．

他们让大家走了。

被动态： We were let go．

大家被允许走开。

D 不定式的进行式可用于如下动词的被动式之后：believe， know，report，say，suppose，think，understand等。

He is believed／known／said／supposed／thought to be living abroad．等于：

People believe／know／say／suppose／think that he is living abroad．

据信／据知／据了解／据猜测／据觉得他住在海外。

You are supposed to be working．等于：

You should be working．

你本应在工作。

在这里也可用不定式的完成进行式：

He is believed to have been waiting for a message．等于：

People believed that he was waiting for a message．

据信他当时一直在等待消息。

You are supposed to have been working．等于：

You should have been working．

你那时本该一直在工作。