关系副词用于引出定语从句，主要有when，where，why。它们后面的句子主干完整，只缺状语，它们都可以等于介词+which也就是说关系副词和关系代词可以相互转化，二者的选择主要看该关系词在从句要充当的句法成分。
关系副词(when、where、why)引导的定语从句，它们后面的句子主干完整，只缺状语，它们都可以等于介词+ which。也就是说关系副词和关系代词可以相互转化，二者的选择主要看该关系词在从句要充当的句法成分。
1、When
指时间，在定语从句中作时间状语。其先行词是表时间的名词(如:time， day， week， month， etc.)。但并非先行词为"时间名词"，就用when引导。当关系词充当定语从句的状语时，用when当关系词充当主语或者宾语时用which或that 引导。
I still remember the day when my brother joined the army.(作状语，when可以转化为on which)
I still remember the days which/that we spent together. (作spent的宾语)
2、Where
指地点在定语从句中作地点状语。其先行词是表示地点的名词(如:place， school， room， etc.)。同理，先行词是"地点名词"时，定语从句可用where引导，还可用which/that引导，取决于该引导词在从句中的成分。
This is the factory where he worked last year. (作状语， where可以转化为in which)
This is the park which/that they visited last year. (作visited的宾语)
3、Why
指原因在定语从句中作原因状语， 先行词通常为reason。同理，先行词为表原因的名词时，还要根据引导词在从句中成分决定用why还是which/that。
The reason why he didn't come to school was that he was ill(作状语).
I don't believe the reason (that/which) he gave me. (作give的宾语)
He asked me the reason that can explain my success. (作explain的主语)
扩展资料
关系副词when，where和why可以用介词+which的形式替换。
1、when=介词+which
I will never forget the day_____ we met for the first time.
解析：先行词是the day，后面的从句恢复到完整句为：we met for the first time on the day.因此，on the day作状语用关系副词when代替，如果用介词+which，就改成on which。答案为when或on which。
2、where =介词+which
This is the farm______ we worked when we were young.
解析：先行词是the farm，后面的从句恢复到完整句为：we worked on the farm when we were young. 因此，on the farm可以用关系副词where代替，如果用介词，就改成on which。
3、why= for which
I don't know the reason ______he did it.
解析：先行词是the reason，后面的从句恢复到完整句为：he did it for the reason. 因此，for the reason可以用关系副词why代替，如果用介词，就改成for which。
