不定式在句中充當成分：

7. 作插入語

插入語（獨立成份）

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. 邏輯主語

(1)用of +n./ pron 來表示邏輯主語:當“be + adj. + 邏輯主語+ to do”結構中的adj. 是absurd, bold, brave, careful, careless, clever, cruel, foolish, honest, kind, nice, polite, rude, silly, thoughtful, considerate, wise, wrong, typical, naughty, selfish, generous等表示人的品行的詞

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 表示邏輯主語:

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.（他給了我他的電話號碼,以便我們需要幫助時與他聯系.）

9. 獨立結構

獨立結構：（不定式的邏輯主語與句子主語不同）該結構在句中一般作說明情況的狀語。

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

(這個計劃是讓爭執的雙方先在基本原則上達成協議，細節以后再磋商。)

Example:

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

不帶“to”的不定式

使用不帶“to”的不定式的幾種句型

(1) 口語中，以why開頭的簡單問句

Why do it that way? 為什么用這種方法來做這事呢？

Why not go out for a walk? 為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...)等習慣用法中

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) 結構中

Last night I did nothing but watch TV.

John will do anything but work on a farm.

但謂語動詞不是do時，but / except所跟的不定式仍須帶“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

一些固定結構中不定式的用法

too ... to 表否定含義,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 之前如有否定詞，不定式也表否定含義

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等與不定式連用表示肯定意義

He's only too pleased to help us. 非常愿意/高興幫助我們。

I shall be only too pleased to come.

too ready to 結構表肯定意義

He's too ready to promise. 他太易于許諾。

He's too ready to criticize others.

不定式的語態

主動語態the last person to leave

被動語態the person to be relied on

當不定式的邏輯主語是不定式動作的承受者，用被動語態

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.

不定式的時態

一般式：to write，to be written

完成：to have written，to have been written

進行：to be writing

完成進行：to have been writing

如不定式動作發生在謂語動作之后(或與之同時發生或將要發生)，用一般時

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（動態動詞）表示的動作與謂語動作發生在同一時間，用進行時

I'm glad to be working with you.

They seem to be having a meeting.

不定式動作先于謂語動作,用完成式

The enemy was reported to have surrendered two days before.

He is said to have translated many articles into English.