2) to + be 的不定式結構，作補語的動詞。

　　acknowledge, believe, consider, think, declare(聲稱)， discover, fancy(設想)， feel, find,　guess, judge, imagine, know, prove, see(理解)， show, suppose, take(以為)， understand

　　We consider Tom to be one of the best students in our class. 我們認為湯姆是班上最好的學生之一。

　　典型例題

　　Charles Babbage is generally considered　___ the first computer.

　　A. to invent　B. inventing　 C. to have invented　 D. having invented

　　答案：A. 由consider to do sth. 排除B、D。. 此句只說明發明這一個事實，不定式后用原形即可。而C為現在完成時，發明為點動詞一般不用完成時，且此處也不強調對現在的影響，因此不選C。

　　3) to be +形容詞

　　seen, appear, be said, be supposed, be believed, be thought, be known, be reported, hope, wish, desire, want, plan, expect, mean

　　The book is believed to be uninteresting.　人們認為這本書沒什么意思。

　　4) there be+不定式

　　believe, expect, intend, like, love, mean, prefer, want, wish, understand

　　We didn't expect there to be so many people there. 我們沒料到會有那么多人在哪里。

　　注意

　　有些動詞需用as 短語做補語，如regard, think believe, take, consider。

　　We regard Tom as our best teacher.　我們認為湯姆是我們最好的老師。

　　Mary took him as her father .　瑪麗把他當作自己的父親。

　　3. 不定式作主語

　　1) It's easy (for me) to do that. 我做這事太容易了。

　　easy, difficult, hard, important, possible, impossible, comfortable, necessary, better;

　　the first, the next, the last, the best, too much, too little, not enough

　　It's so nice to hear your voice.　聽到你的聲音真高興。

　　It's necessary for you to lock the car when you do not use it. 當你不用車的時候，鎖車是有必要的。

　　2) It's very kind of you to help us. 他幫助我們，他真好。

　　kind, nice, stupid, rude, clever, foolish, thoughtful, thoughtless, brave, considerate(考慮周到的)， silly, selfish(自私的)

　　It was silly of us to believe him.　我們真愚蠢，竟然相信了他。

　　It seemed selfish of him not to give them anything.　他不給他們任何東西，這顯得太自私了。

　　注意

　　1) 其他系動詞如，look，appear等也可用于此句型

　　2) 不定式作為句子成分時，動詞用單數形式。

　　3) 當不定式作主語的句子中又有一個不定式作表語時，不能用It is… to…的句型

　　(對)To see is to believe.　百聞不如一見。(錯)It is to believe to see。