1、such后面主要是修饰名词。即：such＋a/an＋adj.＋n.或a/an＋such＋adj.＋n.。如果名词是不可数名词或复数名词，则不可以用不定冠词a或an。如：
①He has such a beautiful bike. We all go to see it.
②It is a such fine day. We al want to go to fly a kite.
2、so后面只能跟形容词或副词。即：和so＋adj.或adv.不过，so后面也可以跟名词，但该名词必须是单数可数名词。用法为：so+形容词+a或an+单数可数名词。如：
①The tiger is so big. And the cat is so small.
②She is so lovely a girl.
3、它们后面还可以与that从句连用。即：such…that和so…that意思是“如此……以致……”。如：
①She is such a clever girl that she can make much progress in math exam.
②His brother is so young that he can not go to school.
注：当名词前的形容词为表示数目的词时，such必须换成so。如：
①There are so many people that we can't go past.
②I ate so much food that I didn't want to go any farther.
注意这一句话：He is such a little boy that he can not read or write.(这一句话中的a little不是“一点”的意思，而是“一个小的”的意思，所以，前面仍然用such.不用so.