(1)疑問詞+不定式結(jié)構(gòu)

疑問詞who，what，which，when，where和how后加不定式可構(gòu)成一種特殊的不定式短語。它在句中可以用作主語、賓語、表語和雙重賓語。如：

When to start has not been decided.何時(shí)動(dòng)身尚未決定。(主語)

I don't know what to do.我不知道該怎么辦。(賓語)

The difficulty was how to cross the river.困難在于如何過河。(表語)

I can tell you where to get this book.我可以告訴你哪里可以買到此書。(雙重賓語)

(注)A.有時(shí)疑問詞前可用介詞，如：

I have no idea of how to do it.我不知道如何做此事。

B.動(dòng)詞know 后面不能直接跟不定式作賓語，只能跟疑問詞(如：how, what)+不定式：

While still a young boy, Tom knew to play the piano well and as he grew older, he wrote operas, the most famous of which is Carmen.

(2)介詞except和but作“只有…，只能…”講時(shí)跟不定式結(jié)構(gòu)(but與不帶to的不定式連用)。

When the streets are full of melting snow, you cannot help but getting your shoes wet.

(3)不帶to的不定式

1)在表示生理感覺的動(dòng)詞后的不定式不帶to。這類詞有：

feel 覺得 observe 注意到，看到 overhear聽到

watch注視 listen to聽 perceive察覺，感知

notice注意 see看見 look at看 hear聽

On seeing the young child fell into the lake，Eric sprang to his feet，and went on the rescue.

2)另一類是某些使役動(dòng)詞，如make, let，have等。如：

Let him do it.讓他做吧。

I would have you know that I am ill.我想要你知道我病了。

(注)：

①上述感覺動(dòng)詞與使役動(dòng)詞轉(zhuǎn)換為被動(dòng)結(jié)構(gòu)時(shí)。其后的不定式一般需帶to，如：

He was seen to come.

The boy was made to go to bed early.

②在動(dòng)詞find與help之后，不定式可帶to亦可不帶to，如：

He was surprised to find the sheep (to) break fence at this season.他發(fā)現(xiàn)羊在此季節(jié)越出柵欄，感到驚訝。

3)在do nothing/anything/everything but(except)結(jié)構(gòu)中。例如：

Last night I did nothing but watch TV.昨天晚上，我除了看電視別的什么也沒有干。

但是，如果謂語動(dòng)詞不是“do nothing，anything，everything”，那么but(except)所跟的不定式則仍須帶。

The doctor told him nothing but to stop smoking.醫(yī)生除了讓他戒煙，其它什么都沒有說。

There was nothing for them to do but to remain silent.除了保持沉默以外，他們沒有別有別的辦法。

(4)不定式與動(dòng)名詞的邏輯主語和分詞獨(dú)立結(jié)構(gòu)

1)不定式的邏輯主語為：for +名詞(或代詞賓格)+ 不定式。例如：

I found it impossible for him to do the job alone.我發(fā)現(xiàn)他—個(gè)人干這活是不可能的。

(注)在表示人物性格、特性等的形容詞后面，常用of引出不定式的邏輯主語。例如：

It was wise of him to do that.他那樣做是明智的。

2)動(dòng)名詞的邏輯主語為;①人稱代詞的所有格+動(dòng)名詞;②名詞‘s+動(dòng)名詞。例如：

Tom insisted on my going with them.他堅(jiān)持要我和他們一起去。

He dislikes his wife's working late.他不喜歡他妻子工作得很晚。

3)某些形容詞，如：careless等不定式后可以加of來引導(dǎo)出其邏輯主語。這類詞主要有：absurd, bold, brave, courageous, careful, careless, clever, wise, foolish, silly, stupid, good, nice, kind thoughtful, considerate, greedy, generous, honest, modest, polite, rude, cruel ,selfish, wicked, wrong等

It is very kind of you to help me.你幫助我太好了。

間或也可用for + there to be表示(而且there后面的不定式只能是to be)。

It's a great pity for there to be much trouble in the company.太遺憾了公司里有這么多的麻煩。

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（責(zé)任編輯：gx）

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