1. 被动式：当不定式的逻辑主语是不定式所表示的动作的承受者时，不定式一般要用被动
　　语态（有时逻辑主语省略），如：
　The meeting is to be held next Monday.
　This is a common method to be adopted for plastic making.
　To be invited to the party is a great honor.

2. 完成式：不定式的动作发生在谓语动作之前用完成式，如：
　I am sorry to have troubled you.
　I believed the book to have been translated into Chinese.

3. 进行式：不定式动作与谓语动词的动作同时发生时用进行式，如：
　Her health seems to be improving.
　She is said to be studying in London.