请问如何区分目的状语从句和结果状语从句？

表示目的状语的从句可以由that, so that, in order that, lest, for fear that, in case等词引导，例如
You must speak louder so that /in order that you can be heard by all.
He wrote the name down for fear that(lest) he should forget it.
Better take more clothes in case the weather is cold.

拜托，认真看下语法书，怎么老是有这么幼稚的问题。