reason 后如果是why 引导的从句 都是定语从句吗?

1.The reason why.这个why引导的应该是定语从句,先行词the reason 在从句中充当原因状语,相当于for which　　例如：I don't know the reason why (for which) she looks unhappy today.
2 The reason that 这个句型中的that引导的可能是定语从句,也可能是同位语从句,关键看先行词在从句中充当什么成分.也就是说从句中缺少主语、宾语或表语时,那肯定是定语从句；从句不缺少成分,是个完整的句子,那肯定是同位语从句.
　　例如：I believe the reason that he gave.定语从句
Tom didn't know the reason that you told me yesterday.
这也是定语从句,因为先行词the reason在从句中充当tell的宾语,还原为you told me the reason yesterday.
　　而下面这个
　　He gave the reason that he got up too late this morning.从句不缺少任何成分,是同位语从句.
你还可以再扩展一个：the reason why ...is that...这个that引导的是表语从句,意思为：.的原因是...