当不定式的逻辑主语是这个不定式所表示的动作的承受者，且不定式的动作发生在谓语动词的动作之前，不定式要用完成被动式，在句中可作主语，宾语或构成复合宾语，复合谓语。
The forest fire is reported to have been put out last night。
It is supposed to have been finished without referring to any reference books。
5. 带逻辑主语的不定式短语
不定式可以有逻辑主语，其构成形式为“for +代词的宾格(或名词) +不定式”。 带逻辑主语的不定式短语可在句子中作主语、宾语、表语或状语等。
It is not easy for you to catch up with them in a short time。
I think it better for you to see the doctor。
What we want is for you to understand the matter clearly。
I sent him some pictures for him to see what Paris is like。
6. 带疑问词的不定式短语
不定式前可以加某些疑问代词，如who、what、which，或疑问副词，如when、where、how、why等，构成一种特殊的不定式短语，可在句子中作主语、宾语、表语或状语等。
How to improve English is often discussed among the students。
We haven’t decided when to visit the place。
The most difficult thing in learning English is how to speak the language well。
You haven’t answered my question where to get these books。
7. 某些动词后的不定式作宾语补足语时，不定式不带to，这些动词是feel， have， hear， let， make， notice， see， watch等。
Suddenly I felt the atmosphere in the room become tense。
I often hear them sing this song。