不定式作定语.这种不定式中,很多和它修饰的词有动宾关系,故如果这个不定式是不及物动词,它后面就应加相应的介词.例如：
Do you have anything more to say?
There is nothing to worry about.
不定式作宾语补足语.动词let,make,haqve,see,hear,watch,notice,feel,observe等后面用不定式作宾补要省去to,而其他动词如ask,tell,want,order,warn要带to.
例如： he didn't want me to go.
Let me help you.