A 不定式結(jié)構(gòu)用在acknowledge，assume，believe，claim，consider，estimate，feel，find，know，presume，report，say，think，under- stand等動詞之后。（參見第245節(jié)。）

People consider／know／think等that he is這種句子有兩種被動形式：

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

He is considered／known／thought etc．to be

同樣：

People said that he was jealous^{1 of her．}

大家說他妒忌她。等于：

It was said that he was

He was said to be jealous of her．

據(jù)了解他妒忌她。

在這兩種結(jié)構(gòu)中，用不定式的后一結(jié)構(gòu)比較簡潔。它主要用于be，盡管有時其他動詞的不定式也可以如此用：

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

大家覺得他學會了對警察有用的狀況。

如句中所想到的內(nèi)容涉及到以前的動作，則用不定式的完成式，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

這種結(jié)構(gòu)可與任何動詞的不定式的完成式連用。

B 不定式結(jié)構(gòu)用在suppose后

1 suppose的被動態(tài)之后可以接任何動詞的不定式的一般式，但這種結(jié)構(gòu)一般都含有這是一種責任、義務(wù)的意思，因此并非同suppose的主動態(tài)（常意為推斷）完全對應(yīng)的形式：

You are supposed to know how to drive．

你本該會開車。等于：

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

會開車是你的責任。／你該了解如何開車。

但He is supposed to be in Paris既可能意思是他應(yīng)該在那里，也會是指大家猜想他在那里。

2 suppose的被動態(tài)后面同樣可以跟任何動詞的不定式的完成式。這種結(jié)構(gòu)可以有責任和義務(wù)的意思，但也常常沒這種含義：

You are supposed to have finished．等于：

You should have finished．

你早就應(yīng)該完成了。

但：

He is supposed to have escaped disguised^{2 as a woman．等于：}

People suppose that he escaped

據(jù)猜測他是喬裝打扮成女性逃跑的。

C 用在被動態(tài)動詞后面的不定式一般是帶to的不定式，盡管主動態(tài)動詞后面可能帶的是不帶to的不定式：

主動態(tài)： We saw them go out．

大家看見他們出去了。

被動態(tài)： They were seen to go out．

有人看見他們出去了。

主動態(tài)： He made us work．

他強迫大家干活。

被動態(tài)： We were made to work．

大家被迫干活。

然而，惟獨let的被動態(tài)后面的不定式不帶to：

主動態(tài)： They let us go．

他們讓大家走了。

被動態(tài)： We were let go．

大家被允許走開。

D 不定式的進行式可用于如下動詞的被動式之后：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．

據(jù)信／據(jù)知／據(jù)了解／據(jù)猜測／據(jù)覺得他住在海外。

You are supposed to be working．等于：

You should be working．

你本應(yīng)在工作。

在這里也可用不定式的完成進行式：

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

People believed that he was waiting for a message．

據(jù)信他當時一直在等待消息。

You are supposed to have been working．等于：

You should have been working．

你那時本該一直在工作。