1. 不定式修饰动词表示目的，如：
　One should eat to live, not live to eat.

　为了更加突出或明确表示目的，不定式还可放在句首或用in order to, so as to的结构，
　如：
　　To catch up with the advanced nations, we must make still greater efforts.
　　We started early in order to catch the first train.
　　We should do physical and chemical experiments so as to know the properties of molecules and atoms.

2. 不定式修饰动词、形容词和副词表示结果: 修饰形容词和副词时常用too … to, (not)
　　enough to, so … as to, such … as to结构，如：
　　What have you done to hurt her so much?
　　He knows too little to speak on the subject.
　　I'm not familiar enough with him to ask him for help.
　　The temperature is so high as to change water into steam.
　　The solution has reached such a temperature as not to need to be heated any more.

　不定式前面和only连用表示没有意想到的结果，如：
　　They lifted a rock only to drop it on their own feet.