too…to 结构通常表示否定意义:

She was too young to understand all that.

enough…to结构则表示肯定意义:

She was not old enough to understand all that.

not too, but too, all too, only too等和不定式连用时,不定式一般不表示否定意义:

He's only too pleased to help her.

so…as (to)这种结构也可用不定式作状语:

Be so kind as to drop in some time when you are free.

如果要说明不定式表示的动作是谁做的, 可以在不定式前加一个for引起的短语:

It is not hard for one to do a bit of good.

It is a great honour for us to be present at this rally.

在以某些形容词(如 kind, good, nice, wise, unwise, clever, silly, wrong, right, foolish, stupid, careless, considerate, rude, naughty, impolite等)作表语时, 不定式前可加一个of引起的短语, 来说明不定式指的是谁的情况:

It's kind of you to think so much of us.

(It is) Awfully good of you to come and meet us.

It's very nice of you to be so considerate.

It's unwise of them to turn down the proposal.

V+ing形式(现在分词及动名词)

形式

完成式: 如果要表示动名词代表的动作在谓语所表示的动作之前发生, 通常用动名词的完成形式.

He didn't mention having met me.

I regret not having taken her advice.

在某些动词后(或成语中), 常用(或可以用)动名词的一般形式, 尽管动作是在谓语所表示的动作之前发生的.

Excuse me for coming late.

I don't remember ever seeing him anywhere.

现在分词的完成式主要用在状语中, 表示这动作在谓语所表示的动作之前发生.

Having been there many times, he offered to be our guide.

Having found the cause, they were able to propose a remedy.

另外, 独立结构也可用现在分词的完成形式.

The guests having left, they resumed their discussion.

The children, having eating their fill, were allowed to leave the table.

被动式: 当一个动名词逻辑上的主语所表示的是这动作的对象时, 动名词一般要用被动形式.

His being neglected by the host added to his uneasiness.

He couldn't bear being made fun of like that.

但要注意, 在want, need, deserve, require 等动词后, 尽管表示的是被动的意思, 却用动名词的主动形式.

My pen needs filling.

The point deserves mentioning.

This problem requires studying with great care.

在worth这个形容词后情形也是这样.

Her method is worth trying.