限制定语从句紧跟先行词，同先行词这间一般不加逗号，仅修饰先行词，可以由关系代词．关系副词或that来引导。非限制性定语从句仅作补充或说明，用逗号与主句隔开，既可修饰先行词，又可修饰整个主句，不可用that引导。
2．关系代词和关系副词的选择依据
弄清代替先行词的关系词在从句中作什么成分,作状语的应选用关系副词，作主语．宾语或表语的可选用关系代词。
3. 先行词与定语从句隔离
定语从句一般紧跟在先行词之后，但定语从句与先行词之间有时也会插入别的成分，构成先行词与定语从句的隔离。例如：
1) This is the article written by him that Is poke to you about.
2) He was the only person in this country who was invited.
