1） 表示目的；它的否定式是so as not to do。
　　 Tom kept quiet about the accident so as not to lose his job.　
　　　　 汤姆对事故保持沉默是为了不丢掉他的工作。
　　 Go in quietly so as not to wake the baby.
　　　　 轻点进去，别惊醒了婴儿。
2)　so kind as to ---劳驾
　　 Would you be so kind as to tell me the time?
　　　　 劳驾，现在几点了。

不定式做定语通常要放在被修饰的词后。例如：
　　　I have a lot of work to do.　
　　　So he made some candles to give light