此外，這種不定式結構還可作主語，表語，和介詞賓語等。

　　How to live a happy life is a difficult question to answer. 怎樣過幸福生活是個很難回答的問題

　　The question is whom to choose for the position. 問題是這個位置選誰。

　　That was a discussion about how to increase their strength. 那是一次關于怎樣增強他們力量的討論。

　　He said nothing about what to do with her. 關于拿她怎么辦，他啥也沒說。

　　She asked my suggestion just now about where to go for her holidays. 關于去哪里度假，她剛才征求了我的意見。

　　3、有些動詞需要不定式作賓語補足語。這種動詞常見的有：ask請求，advise勸告，allow允許，beg乞求，believe相信，call on號召，cause促使，compel強迫，command指揮，direct指導，enable使…能夠，encourage鼓勵，expect期望，feel覺得，force迫使，get使得，hate不喜歡，have使，hear聽見，help幫助，inspire鼓舞，intend 打算,invite邀請,instruct指示，know知道，lead引導，let讓，like喜歡，listen to 聽，look at看，make 使得, notice注意到, observe觀察，order命令，permit允許，persuade說服，prefer更喜歡，press施加壓力，remind提醒，request請求，teach教，tell告訴，urge敦促，want 想要，warn警告，wish希望，等等。

　　I asked my mother to buy a new bike for me. 我請求媽媽給我買輛新自行車。

　　Tony knew his girl friend to be a shy college student. 托尼知道他的女朋友是一個害羞的大學生。

　　They helped you to get on the bus, didn’t they? 他們幫你上了汽車， 是嗎?

　　4、有些動詞要求省掉to的不定式作賓語補語。這樣的動詞有：feel覺得，have使，hear聽見，help幫助，let讓，listen to 聽，look at看，make使，notice 注意，see看見，observe 觀察，watch觀看 等，一類是感官動詞，一類是使役動詞。

　　A policeman saw the accident happen. 一位警察看見事故發生。

　　We listened to her talk about her experience abroad. 我們聽她講國外的經歷。

　　We’d be glad to have you work with us. 我們會很高興有你和我們一起工作。

　　上述help后面的不定式省掉to與保留to都可以。在被動語態中，上述動詞后面的不定式要把省去的to還原。

　　I heard the dog come in. 我聽見那條狗進來。

　　=The dog was heard to come in. 有人聽見那條狗進來。

　　I saw her go out by bike. 我看見她騎著自行車出去了。

　　=She was seen to go out by bike. 有人看見她騎著自行車出去了。

　　Can I help (to) lift this heavy box?   我可以幫著搬起這個沉重的箱子嗎?

　　You may as well help me (to)get things straight. 你不妨幫我把東西整理好。

　　She helped the old woman (to) cross the street. 他幫助那位老婦人過街

　　在had better(最好)，would rather(寧愿)，would sooner(寧愿)，would (just) as soon(寧愿)，cannot but(不能不，不由得不)，cannot help but(不能不，不由得不)等成語后面也跟不帶to的不定式：

　　He would rather listen to others than talk himself. 他寧愿聽別人也不愿自己說。

　　He would sooner play than work. 他寧愿玩也不愿干活。

　　You had better go away right now. 你最好立即就走。

　　I would rather take this method. 我倒愿意采取這個辦法。

　　I’d rather walk than take a bus. 我寧可走也不愿坐公共汽車。

　　She’d rather die than lose the children. 她寧可死也不愿失去孩子們。

　　I’d rather not have eggs and bacon for breakfast.

　　She’d sooner stay at home.

　　I would as soon do it by myself.

　　I would just as soon stay as go. 我寧愿住下也不愿去。