5.作状语
通常表示目的、结果、原因等。如:
i will go(去) to see you. (目的)
in 1972 she left home never to return(返回). (结果)
i am sorry(伤心的, 难过得) to hear that. (原因)
注:
①不定式作目的状语,可以在句首,也可以在句末。有时为了强调可用so as to...(以便,为了)或in order to ...(为了...目的)。
let’s hurry(赶紧) so as to catch(赶上) the last bus.
补充:
catch/get a cold
did you catch my idea? (catch –understand – follow理解)
all living things (生物)must eat(吃) in order to stay(保持) alive(活着的).
 
②不定式作结果状语可用so (such) ...as to (这样(的) ...以至),too...to(太...以至不能),enough to (足以...)等引出,如:
the rain was so heavy(大) as to make our picnic impossible.
 
补充:
heavy traffic 车流量大
他有点胖
he is a little fat? /heavy?.(on a heavy side)
heavy food 油腻的食物
light food 清淡的食物
a heavy smoker 烟瘾很大的人
a heavy drinker 酒量很大的人
 
this man is too lazy(懒惰的) to succeed in(在...方面取得成功) business(生意).
 
③“be+形容词+不定式”的结构中,不定式部分常看作是状语,这类后面通常带不定式结构的形容词有:able(能够的), afraid(害怕的), anxious(渴望的), careful(小心的), determined(决定了的), eager(渴望的), free(自由的), glad(高兴的), pleased(高兴的), ready(情愿的), sorry(抱歉的, 遗憾的), sure(一定的, 必定的), willing(乐意的)等。

6.作补足语
有宾语补足语和主语补足语两种。
1)作宾语补足语
有一些及物动词除跟宾语外,还需要有一个成分作逻辑上的补充说明,使得宾语的状态或行为或特征等的意思完整。这个成分称为补足语,用于说明宾语,因此称宾语补足语。不定式可作宾语补足语,如:
many parents allow their children to make their own decisions.
 
注:
       通常要求带带有“to”的不定式作宾语补足语的动词有:advise(建议, 劝告), allow(允许), ask(要求), cause(造成), consider(认为), expect(期望), find(发现,认为), imagine(想象), tell(命令, 告诫), want(想要), wish(希望)等
 
       要求不带“to”的不定式作宾语补足语的动词(一般为表示“感觉”或“使役”的动词)有: have(让, 使), hear(听到), let(让), make(使), notice(注意到), see(看), watch(注视,看), listen to(听), look at(看)
i saw two men have a quarrel with a woman just now. 刚才我看见两个男人与一个女人发生争吵。
 
       help后面的作宾语补足语的不定式带“to”或不带“to”都可以。
i help mary wash her clothes. 我帮助玛丽洗衣服。
i help mary to wash her clothes. 我帮助玛丽洗衣服。
 
2)作主语补足语
带有宾语补足语的谓语动词变为被动语态时,宾语成了主语,宾语补足语也就相应地成为主语补足语。当动词不定式用作主语补足语时,一律要用带“to”的形式。如:
their children are allowed to make their own decisions.
 
ⅲ不定式的逻辑主语
如要表明不定式或不定式的动作发出者(即逻辑主语),就要在不定式前用for+名词(或代词的宾格),如:
is the road wide enough for two cars to pass?
the conference is too important for you to miss.