被动语态

The man thought to be a fool
They say him to have been rich
He tried not to have mixed up in politics
He ordered the work to start at once

The man was thought to be a fool.
主语是动作的承受者而不是发出者，用被动语态

He is said to have been rich.
say后不可接不定式，但它的被动语态后可接不定式

He tried not to get mixed up in politics.
get作系动词，可代替be，后接过去分词表示被动，have无此功能。

He ordered the work to be started at once.
不定式作宾语补语时，若与宾语是被动关系，要用不定式的被动形式。