不定式在句中充当成分：

7. 作插入语

插入语（独立成份）

To be fair, he has worked hard these days.

We don't like his idea, to tell you the truth.

He is not good at English, to say nothing of French. (let alone French)

8. 逻辑主语

(1)用of +n./ pron 来表示逻辑主语:当“be + adj. + 逻辑主语+ to do”结构中的adj. 是absurd, bold, brave, careful, careless, clever, cruel, foolish, honest, kind, nice, polite, rude, silly, thoughtful, considerate, wise, wrong, typical, naughty, selfish, generous等表示人的品行的词

Examples:

a. It is thoughtful of you to come to see me.

b. I think it wrong of him not to accept our invitation.

c. It is selfish of Tom not to lend his book to Mary.

d. It is generous of you to help me with my work.

(2)用for + n./ pron 表示逻辑主语:

a. It is necessary for the goods to be packed in strong cases.

b. I found it impossible for him to do the job alone.

c. He gave me the phone number in order for me to contact him when we are in need of help.（他给了我他的电话号码,以便我们需要帮助时与他联系.）

9. 独立结构

独立结构：（不定式的逻辑主语与句子主语不同）该结构在句中一般作说明情况的状语。

The plan was that the contending parties should reach an early agreement on basic principles, the details to be worked out later.

(这个计划是让争执的双方先在基本原则上达成协议，细节以后再磋商。)

Example:

He proposed a picnic, he himself to pay the railway tickets, and John to provide the food.

不带“to”的不定式

使用不带“to”的不定式的几种句型

(1) 口语中，以why开头的简单问句

Why do it that way? 为什么用这种方法来做这事呢？

Why not go out for a walk? 为什么不出去散散步呢？

(2) 在had better, would rather... (than)..., would ... rather than, would sooner ... (than), can not but..., can't help but..., may (might) as well... (不妨...)等习惯用法中

Examples:

Since she is angry, we had better let her alone.

Rather than beg in the street, he would prefer to die of hunger. (He would rather die of hunger than beg in the street...)

I couldn't help but wait for the next bus to come.

(3) 在do nothing/anything/everything but (except) 结构中

Last night I did nothing but watch TV.

John will do anything but work on a farm.

但谓语动词不是do时，but / except所跟的不定式仍须带“to”

The doctor told him nothing but to stop smoking.

There was nothing for them to do but to remain silent.

I have no choice/alternative/option but to give in to her power.

不定式的特殊用法

一些固定结构中不定式的用法

too ... to 表否定含义,而enough ... to ... 表肯定

a. It was too cold for us to go shopping.

(= It was so cold that we couldn't...)

b. It was cold enough to freeze our fingers.

但enough to 之前如有否定词，不定式也表否定含义

The water isn't warm enough for us to go swimming.

(=The water isn't warm enough so we can't...)

(all too), only too等与不定式连用表示肯定意义

He's only too pleased to help us. 非常愿意/高兴帮助我们。

I shall be only too pleased to come.

too ready to 结构表肯定意义

He's too ready to promise. 他太易于许诺。

He's too ready to criticize others.

不定式的语态

主动语态the last person to leave

被动语态the person to be relied on

当不定式的逻辑主语是不定式动作的承受者，用被动语态

He is believed to be elected monitor.

The house to be built is our dining room.

The book is said to have been translated into many languages.

It is an honor for me to be asked to speak here.

不定式的时态

一般式：to write，to be written

完成：to have written，to have been written

进行：to be writing

完成进行：to have been writing

如不定式动作发生在谓语动作之后(或与之同时发生或将要发生)，用一般时

He is determined to work harder next term.

I'm sorry to hear the news.

She is supposed to leave for New York next week.

如不定式（动态动词）表示的动作与谓语动作发生在同一时间，用进行时

I'm glad to be working with you.

They seem to be having a meeting.

不定式动作先于谓语动作,用完成式

The enemy was reported to have surrendered two days before.

He is said to have translated many articles into English.